AmaxB
Well-Known Member
This Guide was written for Bulk Cure but can and does apply to small cures when a chamber is used.
Parts that do not apply to a small grower may have been omitted.
All credits to the Universiry of Georgia & parties involved in the creation of this Guide
[Bulletin 884 Reviewed June, 2009 http://athenaeum.libs.uga.edu/bitstream/handle/10724/12062/B884.pdf?sequence=1]
.
Paul E. Sumner
Extension Engineer
J. Michael Moore
Extension Agronomist
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2
Introduction.................................................................................................................................................................3
Harvesting.....................................................................................................................................................................4
[SUP]Har[/SUP][SUP]v[/SUP][SUP]est Only Mature, Ripe Lea[/SUP][SUP]v[/SUP][SUP]es[/SUP][SUP]..................................................................................................[/SUP][SUP]4[/SUP]
[SUP]Container Loading[/SUP][SUP]..............................................................................................................................[/SUP][SUP]4[/SUP]
Curing................................................................................................................................................................................5
[SUP]Purpose of Curing[/SUP][SUP]...............................................................................................................................[/SUP][SUP]5[/SUP]
[SUP]T[/SUP][SUP]emperature[/SUP][SUP]Ad[/SUP][SUP]v[/SUP][SUP]ance Schedule[/SUP][SUP].......................................................................................................[/SUP][SUP]2[/SUP]
[SUP]Humidity[/SUP][SUP]..............................................................................................................................................[/SUP][SUP]6[/SUP]
[SUP]Use of [/SUP][SUP]W[/SUP][SUP]et-Bulb, Dry-Bulb Thermometers[/SUP][SUP].....................................................................................[/SUP][SUP]6[/SUP]
[SUP]Ad[/SUP][SUP]v[/SUP][SUP]ancing [/SUP][SUP]T[/SUP][SUP]emperatures During [/SUP][SUP]Y[/SUP][SUP]ellowing[/SUP][SUP]..................................................................................[/SUP][SUP]6[/SUP]
[SUP]Y[/SUP][SUP]ellowing Considerations[/SUP][SUP]..................................................................................................................[/SUP][SUP]6[/SUP]
[SUP]Length of Time Required for [/SUP][SUP]Y[/SUP][SUP]ellowing[/SUP][SUP]..........................................................................................[/SUP][SUP]7[/SUP]
[SUP]Other [/SUP][SUP]Y[/SUP][SUP]ellowing Consideration[/SUP][SUP]s[/SUP][SUP].......................................................................................................[/SUP][SUP]7[/SUP]
[SUP]W[/SUP][SUP]ilting[/SUP][SUP]..................................................................................................................................................[/SUP][SUP]7[/SUP]
[SUP]Leaf Drying[/SUP][SUP]..........................................................................................................................................[/SUP][SUP]7[/SUP]
[SUP]W[/SUP][SUP]et-Bulb and Dry-Bulb [/SUP][SUP]T[/SUP][SUP]emperatures[/SUP][SUP]............................................................................................[/SUP][SUP]8[/SUP]
[SUP]Stem Drying[/SUP][SUP].........................................................................................................................................[/SUP][SUP]8[/SUP]
CuringProblems........................................................................................................................................................9
[SUP]Soft[/SUP][SUP]Rot .................................................................................................................................................[/SUP][SUP]9[/SUP]
[SUP]S[/SUP][SUP]w[/SUP][SUP]eating[/SUP][SUP]...............................................................................................................................................[/SUP][SUP]9[/SUP]
[SUP]Brown Spo[/SUP][SUP]t[/SUP][SUP]...........................................................................................................................................[/SUP][SUP]9[/SUP]
[SUP]Immature and Slic[/SUP][SUP]k[/SUP][SUP].............................................................................................................................[/SUP][SUP]9[/SUP]
[SUP]Green[/SUP][SUP]...................................................................................................................................................[/SUP][SUP]10[/SUP]
[SUP]Sponged[/SUP][SUP]..............................................................................................................................................[/SUP][SUP]10[/SUP]
[SUP]T[/SUP][SUP]oad[/SUP][SUP]y[/SUP][SUP]...................................................................................................................................................[/SUP][SUP]10[/SUP]
[SUP]Moisture Run Bac[/SUP][SUP]k[/SUP][SUP]............................................................................................................................[/SUP][SUP]10[/SUP]
[SUP]Barn Scal[/SUP][SUP]d[/SUP][SUP]...........................................................................................................................................[/SUP][SUP]11[/SUP]
[SUP]S[/SUP][SUP]w[/SUP][SUP]elled Stems[/SUP][SUP]....................................................................................................................................[/SUP][SUP]11[/SUP]
[SUP]Scorched[/SUP][SUP].............................................................................................................................................[/SUP][SUP]11[/SUP]
Ordering.........................................................................................................................................................................12
EquipmentandBarnMaintenance..............................................................................................................13
[SUP]Har[/SUP][SUP]v[/SUP][SUP]esters[/SUP][SUP]..........................................................................................................................................[/SUP][SUP]13[/SUP]
[SUP]Curing Bar[/SUP][SUP]n[/SUP][SUP]........................................................................................................................................[/SUP][SUP]13[/SUP]
[SUP]Loading Doors[/SUP][SUP]...................................................................................................................................[/SUP][SUP]13[/SUP]
[SUP]Foundation[/SUP][SUP].........................................................................................................................................[/SUP][SUP]13[/SUP]
[SUP]Curing Chambers and Furnace Room[/SUP][SUP]Areas[/SUP][SUP]................................................................................[/SUP][SUP]13[/SUP]
[SUP]Barn Insulation[/SUP][SUP]..................................................................................................................................[/SUP][SUP]14[/SUP]
[SUP]Existing Uninsulated Barns[/SUP][SUP].............................................................................................................[/SUP][SUP]14[/SUP]
[SUP]P[/SUP][SUP]ad Installation[/SUP][SUP]..................................................................................................................................[/SUP][SUP]14[/SUP]
[SUP]Lo[/SUP][SUP]w[/SUP][SUP]er Plenum[/SUP][SUP]...................................................................................................................................[/SUP][SUP]14[/SUP]
AppendixA....................................................................................................................................................................15
[SUP]How to Make a [/SUP][SUP]W[/SUP][SUP]et-Bulb Thermomete[/SUP][SUP]r[/SUP][SUP]........................................................................................[/SUP][SUP]15[/SUP]
[SUP]T[/SUP][SUP]obacco cover photos f[/SUP][SUP]r[/SUP][SUP]om Bugwood.o[/SUP][SUP]r[/SUP][SUP]g by David Jones, Universiry of Geo[/SUP][SUP]r[/SUP][SUP]gia[/SUP]
[SUP]Extension Ag[/SUP][SUP]r[/SUP][SUP]onomist[/SUP]
Introduction
There are two major objectives for curing flue-cured tobacco: (1) to provide temperature and humidity conditions that will encourage certain desirable chemical and biological changes, and (2) to preserve the leaf and retain quality through timely drying. Curing is more than drying the leaf. It improves chemical and physical changes that are necessary for high-quality cured leaf.
Harvesting
Uniformly ripe tobacco is essential for selling top-quality leaf. Under normal conditions, flue-cued tobacco ripens two to four leaves per week; therefore, a harvest rate of two to four leaves per plant per week for five to seven weeks is required. Several factors can influence the maturity and harvest rate. Tobacco grown with recommended fertilizer requirements will tend to ripen normally and produce sufficient pounds. It is recommended that sand lugs (the first two to three leaves to ripen) not be harvested. This tobacco has low level of solids content and is considered undesirable by the manufacturers. Timely harvest is essential to obtain a quality leaf for market. Harvest primings when the leaves appear to be the same color as those of field peas.Another indicator of ripeness is a uniform color (pale green) throughout the leaf when it is held up in sunlight.
Harvest Only Mature, Ripe Leaves
Tobacco leaves reach full maturity a few days before ripening. Mature leaves exhibit a slight
yellowing and puckering between veins and break off the stalk easier than immature leaves. Fully
mature leaves cure easily, and the quality, color and weight are usually good. The best quality cures
occur when the tobacco is allowed to mature in the field. The stages of maturity are: premature,
mature, ripe and overripe. Tobacco harvested in the ripe stage may be cured to give better color,
quality and weight than tobacco harvested in the overripe stage. Overripe tobacco does not color,
yield or sell as well as tobacco harvested and cured at proper maturation. You should let the tobacco
mature but not become too ripe before removing leaves from the stalk.
Cured leaf quality depends on having uniformly mature leaves in the barn. Quality cured leaf is nearly impossible to achieve if several leaf stages of maturity are in the same barn. Tobacco in any one stage of maturity (except premature) can be successfully cured if attention is focused on that one maturity group. Premature tobacco is nearly impossible to cure under any condition. If tobacco of several maturity groups must be harvested at once, a good cure is possible if you keep maturity groups separated using multiple harvests.
Am leaving this paragraph (below) in the event bulk curing is wanted
Container Loading
The introduction of bulk curing barns has led to problems with properly loading bulk containers. Laborers often do not uniformly load containers such as racks, big boxes and medium-sized boxes.
When you pack, do not leave air tunnels or pack lumps of tobacco. Spread tobacco evenly over the entire container as it is being filled. Lumps or wads of tobacco cause tight spots, and the tobacco will
not cure properly. Fill the corners and edges of bulk containers first and pack these slightly tighter than the center. Unless there is uniform air flow to all leaves in the container, there will be leaves or
pockets of leaves that do not cure properly.
To a large extent, the type and condition of the tobacco determine how tightly it can be packed in bulk containers. Lugs (the bottom quarter of the stalk) should not be packed at all.
You can get good results by packing good quality, upstalk, dry tobacco to a density of 15 pounds per ft3. Remember, the tobacco density may increase from morning to afternoon. Tobacco is usually
turgid (swollen with moisture) in the morning, but it may be completely wilted in the afternoon; therefore, do not pack wilted tobacco as tightly as turgid tobacco. Also, containers should fit snugly
together so air does not pass between them. Use a board or other material to block air movement between the doors and the outside container.
Curing
Historically, tobacco curing has been considered an art. Since the use of bulk barns began, growers have had much more control over the curing process. Management skills include understanding the principles of controlling airflow, temperature and humidity in a controlled environment.
Purpose of Curing
Curing develops and preserves the potential quality, flavor and aroma of tobacco. Once the tobacco is in the curing barn, a concerted effort should be made to bring the tobacco to a brilliant color (lemon
orange). Once you achieve the desired color, dry the leaf to preserve that color. Color is important; it indicates that certain chemical changes have taken place, and it is used as an index of leaf quality. It is estimated that 75 percent of the market value of the leaf is based on its color. The first objective is to maintain life in the leaf until the biological processes are complete (yellowing phase) and starch is
converted to sugar. Next, stop bio-chemical activities by removing leaf moisture (leaf drying). Finally, preserve the leaf by drying the stem.
Closely monitor tobacco temperature, humidity and color throughout the curing process. Periodically look through the observation ports to check the wet-bulb, dry-bulb thermometers and notice the
color changes. Care should be taken when opening the loading doors, which may release too much moisture and harm the curing process, especially during yellowing. For updraft barns, place the dry- bulb thermometer under the tobacco near an observation port so you will not have to open the door. Place the wet-bulb thermometer in between racks or on top of the tobacco to get a more accurate indication of wet-bulb temperature. Reverse the location of the thermometers when using down-draft barns.
Temperature Advance Schedule
Depending on the condition of the tobacco, there is considerable variance in advancing the temperature. The following wet-bulb, dry-bulb temperature schedule (Figure 1) should prove effective with
mature, good quality tobacco.
.
.
Humidity
During the yellowing and leaf-drying phases, humidity control is essential to success. Keep in mind that the relative humidity drops as the curing advances. Humidity is controlled through the
vent system by adjusting the fresh air exchange rate. Controlling humidity can extend or shorten the coloring time to get the most desirable color. If the tobacco is drying too quickly (e.g., drying
preceding yellowing), close the vents. Opening the vents will hasten drying.
Remember these points about air and humidity:
1. Air at higher temperatures has more drying potential at the same relative humidity, and
2. At a constant relative humidity, 105oF air will hold twice as much water as 85oF air.
Use of Wet-Bulb, Dry-Bulb Thermometers
The wet-bulb thermometer measures the temperature of the leaf during the early stages of cure; the dry-bulb thermometer measures air temperature. Most growers are familiar with and use the dry-
bulb thermometer, but you also need a wet-bulb thermometer. Since the humidity and the dry-bulb temperature must be controlled, a wet-bulb thermometer is needed to indicate when adjustments in
the vents are necessary. Thermostats should not be used as thermometers because they may not be calibrated to sense the same temperatures as thermometers.
You can buy wet-bulb thermometers a local fuel supply dealer, or you can make one at a fraction of the cost. A homemade wet-bulb thermometer designed especially for a bulk tobacco barn can be used.
See Appendix A for details on constructing a homemade wet-bulb thermometer.
The relationship between the wet-bulb and the dry-bulb temperatures determines the relative humidity within the barn. The closer the wet-bulb temperature is to the dry-bulb temperature, the higher the relative humidity. The relative humidity within the barn determines the drying rate of the leaf. The lower the humidity, the faster the leaf dries; the higher the humidity, the slower the leaf dries. Maintaining the proper wet-bulb temperature not only results in the best possible cures but also minimizes the amount of fuel necessary to cure the tobacco.
Advancing Temperatures During Yellowing
Advancing the dry-bulb temperature and wet-bulb temperature in relation to each other is a critical
feature of curing. When starting a barn, close air intake dampers before turning on the heater. Turn
the heater on and gradually raise the temperature to the yellowing range (Figure 1). Do not raise the
temperature more than 5oF at any one time. Allow about 30 minutes between temperature rises to
provide time for the curing air to become humid.
Yellowing Considerations
Curing each succeeding barn of tobacco as the season progresses requires adjustments in the
curing schedule. For example, tobacco grown under varying climatic and field conditions calls for
different yellowing schedules, with dry-bulb temperatures varying from 95o to 105oF and wet-bulb
temperatures varying from 93o to 97oF.
After each barn of tobacco is harvested, first decide the best way to yellow the tobacco. Consider leaf moisture content, maturity and thickness. Then make a decision at each step along the way about
how long to maintain a given temperature and humidity so the tobacco will complete its yellowing process. Failure to do this may result in dry leaf tips with a set green color. Tobacco with a high mois- ture content requires considerably more moisture removal before color setting than droughty or low- moisture tobacco.
Alter the yellowing schedule throughout the season as the tobacco varies from thin to thick and/or turgid to wilted tobacco with a minimum amount of moisture. For example, immature, wet-weather or drought-grown tobacco should be yellowed at lower temperatures.
Length of Time Required for Yellowing
Normal tobacco is yellowed at varying lengths of time, depending on the stalk position. For example,
primings and lugs should be completely yellowed in 20 to 30 hours. On the other hand, upstalk to-
bacco may require 60 or more hours to obtain the desired color. The quality of certain varieties may
be improved by extending the yellowing period. Certain varieties may sometimes yellow before
starch is converted to sugar, resulting pale, slick, immature tobacco.
Other Yellowing Suggestions
Remove as much moisture as possible during the yellowing phase of curing. With good tobacco, as
much as 20 percent of the moisture can be removed during yellowing.
When the yellowing phase is almost complete, the tobacco should show a good yellow color at the leaf tip with slight green-tinged colors running along the main stem and veins to the butt. Also, the leaf tips and edges should begin to tuck and dry to a bright yellow. When the tobacco throughout the barn reaches the desired color, increase temperature and drying rate. At the end of yellowing, some wilting should have occurred. Avoid flash temperatures that can dry the leaf before yellowing is completed. This sets an undesirable green color.
Wilting
Some wilting occurs before the end of yellowing at the 105oF dry-bulb temperature, but most of
the wilting should take place as the dry-bulb temperature advances from 110o to 118oF. The rate of
temperature advance from 105o to 110oF should be 1o to 1.5oF per hour with a wet-bulb temperature
of 100oF. During the wilting phase, the tobacco loosens considerably and the air can move through
readily. Do not advance the temperature beyond 118oF dry-bulb temperature until wilting is 100
percent complete.
Leaf Drying
When the tobacco leaves have reached the desired yellow color and are thoroughly wilted, the
leaf must be dried. The drying stage is critical because tobacco is sensitive to temperature change.
Impatience to capture a good color often results in advancing the temperature too rapidly and pro-
ducing a browning or barn scald. If the temperature is advanced too slowly, sponging may occur.
There must be positive control of air-flow and temperature during leaf drying to prevent undesirable
color in the cured leaf. To prevent sponging, dry the leaf as rapidly as possible, yet not so rapidly as
to cause scalding.
Wet-Bulb and Dry-Bulb Temperatures
Maintain the wet-bulb temperature near 100oF during leaf drying. Once the tobacco is dry enough
(30 to 40 percent of the moisture removed) to take dry-bulb readings above 135oF, the wet-bulb
temperature is not critical to the quality of the cured leaf. Maintaining a wet-bulb temperature of
110oF or higher, however, tends to conserve fuel.
Stem Drying
Advance the dry-bulb temperature from 135o to 165oF at a rate of 2o to 3oF per hour. Close dampers
gradually during stem drying. Maintain a damper opening sufficient to hold wet-bulb temperature
down to 110oF during the first 12 to 18 hours of stem drying. Dampers are usually closed completely
about the time the leaf is completely dry and the temperature has reached 165oF. Stems should be
killed out at a temperature of 165oF. Due to sugar caramelization, tobacco will turn red when the dry-
bulb temperature is more than 165oF.
Curing Problems
Most curing problems are caused either by improper packing of containers and/or by wet tobacco. Problems occur with all makes of containers packed with wet (from rain or dew) primings or lugs. The problem with wet tobacco has been especially bad with low-stalk tobacco.
Soft Rot
Low-stalk tobacco (primings and lugs) is especially susceptible to soft rot damage during wet harvest conditions. These leaves are close to the ground in the field and are contaminated by barn rot
organisms that stem from bacteria found in many fields. Once the tobacco is in the barn, the moisture and warm temperatures provide an ideal environment for bacterial growth and barn rot to damage
the tobacco. When dry, affected areas develop a black color and follow irregular patterns on the leaf. Prevent soft rot by harvesting tobacco that is completely dry.
Barn rot can be lessened on wet tobacco by operating the fan with dampers wide open and heat off until the surface moisture is removed from the leaf. This may require as long as 48 hours. If heat is added to remove surface moisture (100 percent relative humidity outside), set the thermostat no more than 5oF above the outside air temperature and provide maximum ventilation without setting green color in the leaf. The object is to keep the leaf as dry and cool as possible to prevent multiplication of the barn rot bacteria.
Sweating
Sweating of tobacco is caused by overcrowding and insufficient and ineffective ventilation during the yellowing and wilting phases, resulting in too much moisture remaining in the leaf when the
temperature is raised. This causes super-saturated stagnant air. To prevent sweating, the drying rate should be as fast as possible once the color is set. Remove as much moisture as possible during the
yellowing phase. Increase ventilation as the temperature increases. If water is condensing on the top tiers, close vents until the tobacco is warm, then flush.
Brown Spot
Tobacco damaged by brown spot should be yellowed at a high yellowing temperature. Early, rapid leaf drying will usually stop the spread of brown spot.
Immature and Slick
Immature, slick tobaccos are described as lacking in grain and other elements of quality. The surface of the leaf is smooth and does not have the desirable crepe-like texture, and the leaf is papery, with
little or no elasticity or oiliness. Such tobaccos lack richness of color, are deficient in aroma and have a flat, undesirable taste. They may be compared with fruits that have been harvested green and allow-
ed to ripen in storage – the “field-ripened” flavor is not there. This condition is associated with: (1) improper fertilization, (2) close spacing or topping too high, with attendant shading and greater com-
petition for plant food, water and sunlight, and (3) excess rainfall or over-irrigation, which leaches out the fertilizer and upsets normal growth processes. These conditions often cause yellowing before
ripening, and immature leaf harvesting. Varieties differ in their tendency to produce tobacco of this type.
Green
Green color in the cured leaf results from a failure to break down all the chlorophyll during the curing process. There are several causes of green tobacco:
1. Harvesting the leaves before they are ripe, as happens when too many leaves are pulled at once. Tobacco leaves sometimes acquire a faded-out yellow color, suggesting ripeness that is not true ripeness.
2. Severe drought conditions, which prevent ripening. Leaves that are harvested under such conditions will generally cure with a greenish cast.
3. Excessive nitrogen supply, which prevents proper ripening. Tobacco grown with too much available nitrogen will cure out green or brown.
4. Insufficient yellowing of the leaves before drying.
There are other deficiencies associated with green color, and such tobacco has a harsh, bitter taste Lighter shades of green will improve on aging, but pronounced green grades are most undesirable.
Sponged
The term “sponged” is used to designate those well-grained, porous, overripe tobaccos that have a dull, grayish-brown color. This type of cured leaf is caused by allowing tobacco of good quality
to become overripe in the field, or by holding low temperatures too long in the early part of the curing process (occurs at high humidity and low temperature (105o - 125oF)). If the moisture in the
leaves is not removed quickly enough, sponging is likely to take place and result in grayish and brownish blotches on the leaf surface. In normal curing, the color breakdown proceeds from green to
yellow. By drying, the color may be fixed at either of these stages. In the case of sponging, the color breakdown has gone beyond the yellow stage to the gray or brown stage. Color alone is not the basis
for designating tobaccos as sponged. Some brown tobaccos may be slick, dead, “toady” or otherwise very undesirable. Slight sponging may not result in serious detriment to quality.
Toady
Toady tobacco is characterized by a slick, dense, sometimes thick and leathery leaf with a nondescript smutty, grayish-brown color. Toady leaves have no grain and are very compact. They are abnormally
high in sugar content. They are usually soggy, but may be dry-natured and starchy. The cause of toadiness is not fully understood; however, certain varieties tend to produce higher proportions of
this type of leaf than others. It has also been observed that in seasons of high rainfall or following over-irrigation, some toady tobacco may be found in all varieties. Rapid drying is essential to
discourage the development of this condition.
Moisture Run Back
The presence of dark or reddish areas along the upper portions of the leaf midrib and larger lateral veins is known as “moisture run back” or “circle stem.” It is caused by lowering the temperature
after the blade of the leaf is dry, but before all moisture has been removed from the midrib. The moisture in the midrib seeps back into the leaf, causing a dark area. Re-firing and drying the midrib will
not remove the discoloration, but will put the tobacco in a safe keeping condition. Run back will not occur if the curing unit is fired continuously until the entire leaf is fully dry.
Barn Scald
Dark, chocolate-colored areas on cured leaves, known as barn scald, may result from excessive humidity in the curing barn. This condition is usually caused by over-crowding in the barn and in-
adequate ventilation. Barn scald may occur at any dry-bulb temperature above 110oF. The leaves are cooked (rather than dried) when the temperature is raised. Brown scald will also occur in properly
loaded barns if killing heat is applied before drying is complete. A set green color, or green scald, may develop in the leaf tips if flash heat occurs before the tobacco is yellowed.
Swelled Stems
After colors have been set and the leaf partially dried (130o to 145oF), the remaining moisture is removed at “killing out” temperatures of approximately 165oF. Failure to remove all moisture from
the midrib leaves it soft, pliable and larger than when dry. Temperature may be too low or held too briefly. Incompletely-dried midribs are called “swelled stems.” Swelled stems usually mold
in storage and may be the cause of considerable loss through damage to the surrounding tobacco. Swelled stems can be reduced by holding temperatures high (165oF) until the stem is dried. Some
curing barns have areas of ineffective ventilation that contribute to swelled stems. Care should be taken to pack containers uniformly to ensure uniform distribution of curing air.
Scorched
This condition is associated with high temperatures, especially during the stem-drying phase. Scorched tobacco has an abnormal aroma and an off-taste when smoked. To keep scorched tobacco to
a minimum, keep dry-bulb temperatures below 165oF.
Ordering
When curing is over and the stems have been killed, the moisture content of the leaves is near zero. At this stage, the leaves and stems are too brittle to handle, so enough moisture must be added to the leaf to bring the moisture content up to about 15 percent. The leaves are then pliable and can be handled easily.
The rate at which to add moisture to the leaf depends mainly on the method selected to add moisture to the barn (OR CHAMBER) and on the condition of the tobacco itself. A barn of 3,000 pounds cured tobacco requires about 50 gallons of water to bring the leaf into order. Running the fan with the dampers wide open usually brings the tobacco in order overnight. There are many spray-injection systems that can bring a barn of tobacco in order in a few hours. If there is a floor in the curing barn, water can be poured onto the floor. No matter which method is selected, do not apply the water directly to the leaf. The ordering method depends on the equipment available and how quickly you need to get the tobacco in order.
The best time to add moisture back into tobacco is when the leaf temperature is high (165F). The following bit about a nozzle is cool, but I just stick a pan of water on my griddle in the chamber.
Turn the furnace off and insert a hollow cone spray nozzle operating at 100 psi (if possible) into the air stream around the furnace. Using this method, a cured barn of tobacco can be made easy to handle in one to two hours. Table 1 lists different types of hollow cone nozzles and hours of operation to add moisture to cured tobacco.)
Appendix A or you can use my method to make a Wet / Dry Bulb Set-Up
http://wholeleaftobaccollc.com/foru...mometer-Set-Up-on-the-CHEAP&p=49765#post49765
Appendix A
How to Make a Wet-Bulb Thermometer
Proper management of the curing process and proper barn maintenance can reduce fuel usage drastically. No matter what type of bulk barn is used, fuel consumption can be reduced by tightening up
the barn and using a wet-bulb thermometer to gauge ventilation. Caulking compound for structural cracks and new weather stripping for doors cost a small amount compared to the heat they save. You
can make a wet-bulb thermometer for $3.00 to $5.00. The homemade wet-bulb thermometer shown in this photograph has been used successfully as an indicator of wet-bulb temperature in bulk barns.
Materials
2 - pieces 1” PVC pipe, 7” long (one piece with 1/4” hole
drilled 1 1/2” from one end)
1 - piece 1” PVC pipe, 2” long
2 - 90o 1” PVC elbows
2 - end caps, 1” PVC
1 - piece athletic shoestring, 7” long (wick)
1 - Tobacco Curing Thermometer with bulb guards cut out
1 - wide rubber band
1 - piece of thread (not shown) 4” long to tie wick to
thermometer bulb
Instructions for Construction, Filling and Using
1. Glue all PVC pipe together as shown in the figure.
2. Carefully remove glass thermometer bulb from holder
and cut out in a 1 to 1 1/2” square around the bulb.
3. Replace glass thermometer bulb and calibrate according to another thermometer.
4. Secure thermometer to PVC pipe with rubber band or light gauge wire.
5. Fill with water. A large syringe or a small snout
“squeeze-it”-type plastic detergent bottle may be helpful.
6. Insert wick into water. A small nail, large toothpick or kitchen matchstick may be helpful.
7. Place in curing barn where air flow is strong. In up-draft barns (e.g., Roanoke, Long, Powell),
lay wet-bulb device flat on its back on the perforated floor near the loading doors. In down-draft
barns (e.g., bulk tobacco), lay wet-bulb device flat on its back near the loading doors where air
flow will strike the wet bulb of the thermometer.
8. Open fresh air vents only enough to maintain a wet-bulb temperature of 100o to 105oF during leaf drying and 105o to 110oF during stem drying.
The finished product
I think I got it all here and is right...
Hope I don't get into trouble for this post - Happy Curing of Your Baccy Crops.
Parts that do not apply to a small grower may have been omitted.
All credits to the Universiry of Georgia & parties involved in the creation of this Guide
[Bulletin 884 Reviewed June, 2009 http://athenaeum.libs.uga.edu/bitstream/handle/10724/12062/B884.pdf?sequence=1]
.
Harvesting and Curing
Flue-Cured Tobacco
Flue-Cured Tobacco
Paul E. Sumner
Extension Engineer
J. Michael Moore
Extension Agronomist
.
2
Introduction.................................................................................................................................................................3
Harvesting.....................................................................................................................................................................4
[SUP]Har[/SUP][SUP]v[/SUP][SUP]est Only Mature, Ripe Lea[/SUP][SUP]v[/SUP][SUP]es[/SUP][SUP]..................................................................................................[/SUP][SUP]4[/SUP]
[SUP]Container Loading[/SUP][SUP]..............................................................................................................................[/SUP][SUP]4[/SUP]
Curing................................................................................................................................................................................5
[SUP]Purpose of Curing[/SUP][SUP]...............................................................................................................................[/SUP][SUP]5[/SUP]
[SUP]T[/SUP][SUP]emperature[/SUP][SUP]Ad[/SUP][SUP]v[/SUP][SUP]ance Schedule[/SUP][SUP].......................................................................................................[/SUP][SUP]2[/SUP]
[SUP]Humidity[/SUP][SUP]..............................................................................................................................................[/SUP][SUP]6[/SUP]
[SUP]Use of [/SUP][SUP]W[/SUP][SUP]et-Bulb, Dry-Bulb Thermometers[/SUP][SUP].....................................................................................[/SUP][SUP]6[/SUP]
[SUP]Ad[/SUP][SUP]v[/SUP][SUP]ancing [/SUP][SUP]T[/SUP][SUP]emperatures During [/SUP][SUP]Y[/SUP][SUP]ellowing[/SUP][SUP]..................................................................................[/SUP][SUP]6[/SUP]
[SUP]Y[/SUP][SUP]ellowing Considerations[/SUP][SUP]..................................................................................................................[/SUP][SUP]6[/SUP]
[SUP]Length of Time Required for [/SUP][SUP]Y[/SUP][SUP]ellowing[/SUP][SUP]..........................................................................................[/SUP][SUP]7[/SUP]
[SUP]Other [/SUP][SUP]Y[/SUP][SUP]ellowing Consideration[/SUP][SUP]s[/SUP][SUP].......................................................................................................[/SUP][SUP]7[/SUP]
[SUP]W[/SUP][SUP]ilting[/SUP][SUP]..................................................................................................................................................[/SUP][SUP]7[/SUP]
[SUP]Leaf Drying[/SUP][SUP]..........................................................................................................................................[/SUP][SUP]7[/SUP]
[SUP]W[/SUP][SUP]et-Bulb and Dry-Bulb [/SUP][SUP]T[/SUP][SUP]emperatures[/SUP][SUP]............................................................................................[/SUP][SUP]8[/SUP]
[SUP]Stem Drying[/SUP][SUP].........................................................................................................................................[/SUP][SUP]8[/SUP]
CuringProblems........................................................................................................................................................9
[SUP]Soft[/SUP][SUP]Rot .................................................................................................................................................[/SUP][SUP]9[/SUP]
[SUP]S[/SUP][SUP]w[/SUP][SUP]eating[/SUP][SUP]...............................................................................................................................................[/SUP][SUP]9[/SUP]
[SUP]Brown Spo[/SUP][SUP]t[/SUP][SUP]...........................................................................................................................................[/SUP][SUP]9[/SUP]
[SUP]Immature and Slic[/SUP][SUP]k[/SUP][SUP].............................................................................................................................[/SUP][SUP]9[/SUP]
[SUP]Green[/SUP][SUP]...................................................................................................................................................[/SUP][SUP]10[/SUP]
[SUP]Sponged[/SUP][SUP]..............................................................................................................................................[/SUP][SUP]10[/SUP]
[SUP]T[/SUP][SUP]oad[/SUP][SUP]y[/SUP][SUP]...................................................................................................................................................[/SUP][SUP]10[/SUP]
[SUP]Moisture Run Bac[/SUP][SUP]k[/SUP][SUP]............................................................................................................................[/SUP][SUP]10[/SUP]
[SUP]Barn Scal[/SUP][SUP]d[/SUP][SUP]...........................................................................................................................................[/SUP][SUP]11[/SUP]
[SUP]S[/SUP][SUP]w[/SUP][SUP]elled Stems[/SUP][SUP]....................................................................................................................................[/SUP][SUP]11[/SUP]
[SUP]Scorched[/SUP][SUP].............................................................................................................................................[/SUP][SUP]11[/SUP]
Ordering.........................................................................................................................................................................12
EquipmentandBarnMaintenance..............................................................................................................13
[SUP]Har[/SUP][SUP]v[/SUP][SUP]esters[/SUP][SUP]..........................................................................................................................................[/SUP][SUP]13[/SUP]
[SUP]Curing Bar[/SUP][SUP]n[/SUP][SUP]........................................................................................................................................[/SUP][SUP]13[/SUP]
[SUP]Loading Doors[/SUP][SUP]...................................................................................................................................[/SUP][SUP]13[/SUP]
[SUP]Foundation[/SUP][SUP].........................................................................................................................................[/SUP][SUP]13[/SUP]
[SUP]Curing Chambers and Furnace Room[/SUP][SUP]Areas[/SUP][SUP]................................................................................[/SUP][SUP]13[/SUP]
[SUP]Barn Insulation[/SUP][SUP]..................................................................................................................................[/SUP][SUP]14[/SUP]
[SUP]Existing Uninsulated Barns[/SUP][SUP].............................................................................................................[/SUP][SUP]14[/SUP]
[SUP]P[/SUP][SUP]ad Installation[/SUP][SUP]..................................................................................................................................[/SUP][SUP]14[/SUP]
[SUP]Lo[/SUP][SUP]w[/SUP][SUP]er Plenum[/SUP][SUP]...................................................................................................................................[/SUP][SUP]14[/SUP]
AppendixA....................................................................................................................................................................15
[SUP]How to Make a [/SUP][SUP]W[/SUP][SUP]et-Bulb Thermomete[/SUP][SUP]r[/SUP][SUP]........................................................................................[/SUP][SUP]15[/SUP]
[SUP]T[/SUP][SUP]obacco cover photos f[/SUP][SUP]r[/SUP][SUP]om Bugwood.o[/SUP][SUP]r[/SUP][SUP]g by David Jones, Universiry of Geo[/SUP][SUP]r[/SUP][SUP]gia[/SUP]
[SUP]Extension Ag[/SUP][SUP]r[/SUP][SUP]onomist[/SUP]
Introduction
There are two major objectives for curing flue-cured tobacco: (1) to provide temperature and humidity conditions that will encourage certain desirable chemical and biological changes, and (2) to preserve the leaf and retain quality through timely drying. Curing is more than drying the leaf. It improves chemical and physical changes that are necessary for high-quality cured leaf.
Harvesting
Uniformly ripe tobacco is essential for selling top-quality leaf. Under normal conditions, flue-cued tobacco ripens two to four leaves per week; therefore, a harvest rate of two to four leaves per plant per week for five to seven weeks is required. Several factors can influence the maturity and harvest rate. Tobacco grown with recommended fertilizer requirements will tend to ripen normally and produce sufficient pounds. It is recommended that sand lugs (the first two to three leaves to ripen) not be harvested. This tobacco has low level of solids content and is considered undesirable by the manufacturers. Timely harvest is essential to obtain a quality leaf for market. Harvest primings when the leaves appear to be the same color as those of field peas.Another indicator of ripeness is a uniform color (pale green) throughout the leaf when it is held up in sunlight.
Harvest Only Mature, Ripe Leaves
Tobacco leaves reach full maturity a few days before ripening. Mature leaves exhibit a slight
yellowing and puckering between veins and break off the stalk easier than immature leaves. Fully
mature leaves cure easily, and the quality, color and weight are usually good. The best quality cures
occur when the tobacco is allowed to mature in the field. The stages of maturity are: premature,
mature, ripe and overripe. Tobacco harvested in the ripe stage may be cured to give better color,
quality and weight than tobacco harvested in the overripe stage. Overripe tobacco does not color,
yield or sell as well as tobacco harvested and cured at proper maturation. You should let the tobacco
mature but not become too ripe before removing leaves from the stalk.
Cured leaf quality depends on having uniformly mature leaves in the barn. Quality cured leaf is nearly impossible to achieve if several leaf stages of maturity are in the same barn. Tobacco in any one stage of maturity (except premature) can be successfully cured if attention is focused on that one maturity group. Premature tobacco is nearly impossible to cure under any condition. If tobacco of several maturity groups must be harvested at once, a good cure is possible if you keep maturity groups separated using multiple harvests.
Am leaving this paragraph (below) in the event bulk curing is wanted
Container Loading
The introduction of bulk curing barns has led to problems with properly loading bulk containers. Laborers often do not uniformly load containers such as racks, big boxes and medium-sized boxes.
When you pack, do not leave air tunnels or pack lumps of tobacco. Spread tobacco evenly over the entire container as it is being filled. Lumps or wads of tobacco cause tight spots, and the tobacco will
not cure properly. Fill the corners and edges of bulk containers first and pack these slightly tighter than the center. Unless there is uniform air flow to all leaves in the container, there will be leaves or
pockets of leaves that do not cure properly.
To a large extent, the type and condition of the tobacco determine how tightly it can be packed in bulk containers. Lugs (the bottom quarter of the stalk) should not be packed at all.
You can get good results by packing good quality, upstalk, dry tobacco to a density of 15 pounds per ft3. Remember, the tobacco density may increase from morning to afternoon. Tobacco is usually
turgid (swollen with moisture) in the morning, but it may be completely wilted in the afternoon; therefore, do not pack wilted tobacco as tightly as turgid tobacco. Also, containers should fit snugly
together so air does not pass between them. Use a board or other material to block air movement between the doors and the outside container.
Curing
Historically, tobacco curing has been considered an art. Since the use of bulk barns began, growers have had much more control over the curing process. Management skills include understanding the principles of controlling airflow, temperature and humidity in a controlled environment.
Purpose of Curing
Curing develops and preserves the potential quality, flavor and aroma of tobacco. Once the tobacco is in the curing barn, a concerted effort should be made to bring the tobacco to a brilliant color (lemon
orange). Once you achieve the desired color, dry the leaf to preserve that color. Color is important; it indicates that certain chemical changes have taken place, and it is used as an index of leaf quality. It is estimated that 75 percent of the market value of the leaf is based on its color. The first objective is to maintain life in the leaf until the biological processes are complete (yellowing phase) and starch is
converted to sugar. Next, stop bio-chemical activities by removing leaf moisture (leaf drying). Finally, preserve the leaf by drying the stem.
Closely monitor tobacco temperature, humidity and color throughout the curing process. Periodically look through the observation ports to check the wet-bulb, dry-bulb thermometers and notice the
color changes. Care should be taken when opening the loading doors, which may release too much moisture and harm the curing process, especially during yellowing. For updraft barns, place the dry- bulb thermometer under the tobacco near an observation port so you will not have to open the door. Place the wet-bulb thermometer in between racks or on top of the tobacco to get a more accurate indication of wet-bulb temperature. Reverse the location of the thermometers when using down-draft barns.
Temperature Advance Schedule
Depending on the condition of the tobacco, there is considerable variance in advancing the temperature. The following wet-bulb, dry-bulb temperature schedule (Figure 1) should prove effective with
mature, good quality tobacco.
.
.
Humidity
During the yellowing and leaf-drying phases, humidity control is essential to success. Keep in mind that the relative humidity drops as the curing advances. Humidity is controlled through the
vent system by adjusting the fresh air exchange rate. Controlling humidity can extend or shorten the coloring time to get the most desirable color. If the tobacco is drying too quickly (e.g., drying
preceding yellowing), close the vents. Opening the vents will hasten drying.
Remember these points about air and humidity:
1. Air at higher temperatures has more drying potential at the same relative humidity, and
2. At a constant relative humidity, 105oF air will hold twice as much water as 85oF air.
Use of Wet-Bulb, Dry-Bulb Thermometers
The wet-bulb thermometer measures the temperature of the leaf during the early stages of cure; the dry-bulb thermometer measures air temperature. Most growers are familiar with and use the dry-
bulb thermometer, but you also need a wet-bulb thermometer. Since the humidity and the dry-bulb temperature must be controlled, a wet-bulb thermometer is needed to indicate when adjustments in
the vents are necessary. Thermostats should not be used as thermometers because they may not be calibrated to sense the same temperatures as thermometers.
You can buy wet-bulb thermometers a local fuel supply dealer, or you can make one at a fraction of the cost. A homemade wet-bulb thermometer designed especially for a bulk tobacco barn can be used.
See Appendix A for details on constructing a homemade wet-bulb thermometer.
The relationship between the wet-bulb and the dry-bulb temperatures determines the relative humidity within the barn. The closer the wet-bulb temperature is to the dry-bulb temperature, the higher the relative humidity. The relative humidity within the barn determines the drying rate of the leaf. The lower the humidity, the faster the leaf dries; the higher the humidity, the slower the leaf dries. Maintaining the proper wet-bulb temperature not only results in the best possible cures but also minimizes the amount of fuel necessary to cure the tobacco.
Advancing Temperatures During Yellowing
Advancing the dry-bulb temperature and wet-bulb temperature in relation to each other is a critical
feature of curing. When starting a barn, close air intake dampers before turning on the heater. Turn
the heater on and gradually raise the temperature to the yellowing range (Figure 1). Do not raise the
temperature more than 5oF at any one time. Allow about 30 minutes between temperature rises to
provide time for the curing air to become humid.
Yellowing Considerations
Curing each succeeding barn of tobacco as the season progresses requires adjustments in the
curing schedule. For example, tobacco grown under varying climatic and field conditions calls for
different yellowing schedules, with dry-bulb temperatures varying from 95o to 105oF and wet-bulb
temperatures varying from 93o to 97oF.
After each barn of tobacco is harvested, first decide the best way to yellow the tobacco. Consider leaf moisture content, maturity and thickness. Then make a decision at each step along the way about
how long to maintain a given temperature and humidity so the tobacco will complete its yellowing process. Failure to do this may result in dry leaf tips with a set green color. Tobacco with a high mois- ture content requires considerably more moisture removal before color setting than droughty or low- moisture tobacco.
Alter the yellowing schedule throughout the season as the tobacco varies from thin to thick and/or turgid to wilted tobacco with a minimum amount of moisture. For example, immature, wet-weather or drought-grown tobacco should be yellowed at lower temperatures.
Length of Time Required for Yellowing
Normal tobacco is yellowed at varying lengths of time, depending on the stalk position. For example,
primings and lugs should be completely yellowed in 20 to 30 hours. On the other hand, upstalk to-
bacco may require 60 or more hours to obtain the desired color. The quality of certain varieties may
be improved by extending the yellowing period. Certain varieties may sometimes yellow before
starch is converted to sugar, resulting pale, slick, immature tobacco.
Other Yellowing Suggestions
Remove as much moisture as possible during the yellowing phase of curing. With good tobacco, as
much as 20 percent of the moisture can be removed during yellowing.
When the yellowing phase is almost complete, the tobacco should show a good yellow color at the leaf tip with slight green-tinged colors running along the main stem and veins to the butt. Also, the leaf tips and edges should begin to tuck and dry to a bright yellow. When the tobacco throughout the barn reaches the desired color, increase temperature and drying rate. At the end of yellowing, some wilting should have occurred. Avoid flash temperatures that can dry the leaf before yellowing is completed. This sets an undesirable green color.
Wilting
Some wilting occurs before the end of yellowing at the 105oF dry-bulb temperature, but most of
the wilting should take place as the dry-bulb temperature advances from 110o to 118oF. The rate of
temperature advance from 105o to 110oF should be 1o to 1.5oF per hour with a wet-bulb temperature
of 100oF. During the wilting phase, the tobacco loosens considerably and the air can move through
readily. Do not advance the temperature beyond 118oF dry-bulb temperature until wilting is 100
percent complete.
Leaf Drying
When the tobacco leaves have reached the desired yellow color and are thoroughly wilted, the
leaf must be dried. The drying stage is critical because tobacco is sensitive to temperature change.
Impatience to capture a good color often results in advancing the temperature too rapidly and pro-
ducing a browning or barn scald. If the temperature is advanced too slowly, sponging may occur.
There must be positive control of air-flow and temperature during leaf drying to prevent undesirable
color in the cured leaf. To prevent sponging, dry the leaf as rapidly as possible, yet not so rapidly as
to cause scalding.
Wet-Bulb and Dry-Bulb Temperatures
Maintain the wet-bulb temperature near 100oF during leaf drying. Once the tobacco is dry enough
(30 to 40 percent of the moisture removed) to take dry-bulb readings above 135oF, the wet-bulb
temperature is not critical to the quality of the cured leaf. Maintaining a wet-bulb temperature of
110oF or higher, however, tends to conserve fuel.
Stem Drying
Advance the dry-bulb temperature from 135o to 165oF at a rate of 2o to 3oF per hour. Close dampers
gradually during stem drying. Maintain a damper opening sufficient to hold wet-bulb temperature
down to 110oF during the first 12 to 18 hours of stem drying. Dampers are usually closed completely
about the time the leaf is completely dry and the temperature has reached 165oF. Stems should be
killed out at a temperature of 165oF. Due to sugar caramelization, tobacco will turn red when the dry-
bulb temperature is more than 165oF.
Curing Problems
Most curing problems are caused either by improper packing of containers and/or by wet tobacco. Problems occur with all makes of containers packed with wet (from rain or dew) primings or lugs. The problem with wet tobacco has been especially bad with low-stalk tobacco.
Soft Rot
Low-stalk tobacco (primings and lugs) is especially susceptible to soft rot damage during wet harvest conditions. These leaves are close to the ground in the field and are contaminated by barn rot
organisms that stem from bacteria found in many fields. Once the tobacco is in the barn, the moisture and warm temperatures provide an ideal environment for bacterial growth and barn rot to damage
the tobacco. When dry, affected areas develop a black color and follow irregular patterns on the leaf. Prevent soft rot by harvesting tobacco that is completely dry.
Barn rot can be lessened on wet tobacco by operating the fan with dampers wide open and heat off until the surface moisture is removed from the leaf. This may require as long as 48 hours. If heat is added to remove surface moisture (100 percent relative humidity outside), set the thermostat no more than 5oF above the outside air temperature and provide maximum ventilation without setting green color in the leaf. The object is to keep the leaf as dry and cool as possible to prevent multiplication of the barn rot bacteria.
Sweating
Sweating of tobacco is caused by overcrowding and insufficient and ineffective ventilation during the yellowing and wilting phases, resulting in too much moisture remaining in the leaf when the
temperature is raised. This causes super-saturated stagnant air. To prevent sweating, the drying rate should be as fast as possible once the color is set. Remove as much moisture as possible during the
yellowing phase. Increase ventilation as the temperature increases. If water is condensing on the top tiers, close vents until the tobacco is warm, then flush.
Brown Spot
Tobacco damaged by brown spot should be yellowed at a high yellowing temperature. Early, rapid leaf drying will usually stop the spread of brown spot.
Immature and Slick
Immature, slick tobaccos are described as lacking in grain and other elements of quality. The surface of the leaf is smooth and does not have the desirable crepe-like texture, and the leaf is papery, with
little or no elasticity or oiliness. Such tobaccos lack richness of color, are deficient in aroma and have a flat, undesirable taste. They may be compared with fruits that have been harvested green and allow-
ed to ripen in storage – the “field-ripened” flavor is not there. This condition is associated with: (1) improper fertilization, (2) close spacing or topping too high, with attendant shading and greater com-
petition for plant food, water and sunlight, and (3) excess rainfall or over-irrigation, which leaches out the fertilizer and upsets normal growth processes. These conditions often cause yellowing before
ripening, and immature leaf harvesting. Varieties differ in their tendency to produce tobacco of this type.
Green
Green color in the cured leaf results from a failure to break down all the chlorophyll during the curing process. There are several causes of green tobacco:
1. Harvesting the leaves before they are ripe, as happens when too many leaves are pulled at once. Tobacco leaves sometimes acquire a faded-out yellow color, suggesting ripeness that is not true ripeness.
2. Severe drought conditions, which prevent ripening. Leaves that are harvested under such conditions will generally cure with a greenish cast.
3. Excessive nitrogen supply, which prevents proper ripening. Tobacco grown with too much available nitrogen will cure out green or brown.
4. Insufficient yellowing of the leaves before drying.
There are other deficiencies associated with green color, and such tobacco has a harsh, bitter taste Lighter shades of green will improve on aging, but pronounced green grades are most undesirable.
Sponged
The term “sponged” is used to designate those well-grained, porous, overripe tobaccos that have a dull, grayish-brown color. This type of cured leaf is caused by allowing tobacco of good quality
to become overripe in the field, or by holding low temperatures too long in the early part of the curing process (occurs at high humidity and low temperature (105o - 125oF)). If the moisture in the
leaves is not removed quickly enough, sponging is likely to take place and result in grayish and brownish blotches on the leaf surface. In normal curing, the color breakdown proceeds from green to
yellow. By drying, the color may be fixed at either of these stages. In the case of sponging, the color breakdown has gone beyond the yellow stage to the gray or brown stage. Color alone is not the basis
for designating tobaccos as sponged. Some brown tobaccos may be slick, dead, “toady” or otherwise very undesirable. Slight sponging may not result in serious detriment to quality.
Toady
Toady tobacco is characterized by a slick, dense, sometimes thick and leathery leaf with a nondescript smutty, grayish-brown color. Toady leaves have no grain and are very compact. They are abnormally
high in sugar content. They are usually soggy, but may be dry-natured and starchy. The cause of toadiness is not fully understood; however, certain varieties tend to produce higher proportions of
this type of leaf than others. It has also been observed that in seasons of high rainfall or following over-irrigation, some toady tobacco may be found in all varieties. Rapid drying is essential to
discourage the development of this condition.
Moisture Run Back
The presence of dark or reddish areas along the upper portions of the leaf midrib and larger lateral veins is known as “moisture run back” or “circle stem.” It is caused by lowering the temperature
after the blade of the leaf is dry, but before all moisture has been removed from the midrib. The moisture in the midrib seeps back into the leaf, causing a dark area. Re-firing and drying the midrib will
not remove the discoloration, but will put the tobacco in a safe keeping condition. Run back will not occur if the curing unit is fired continuously until the entire leaf is fully dry.
Barn Scald
Dark, chocolate-colored areas on cured leaves, known as barn scald, may result from excessive humidity in the curing barn. This condition is usually caused by over-crowding in the barn and in-
adequate ventilation. Barn scald may occur at any dry-bulb temperature above 110oF. The leaves are cooked (rather than dried) when the temperature is raised. Brown scald will also occur in properly
loaded barns if killing heat is applied before drying is complete. A set green color, or green scald, may develop in the leaf tips if flash heat occurs before the tobacco is yellowed.
Swelled Stems
After colors have been set and the leaf partially dried (130o to 145oF), the remaining moisture is removed at “killing out” temperatures of approximately 165oF. Failure to remove all moisture from
the midrib leaves it soft, pliable and larger than when dry. Temperature may be too low or held too briefly. Incompletely-dried midribs are called “swelled stems.” Swelled stems usually mold
in storage and may be the cause of considerable loss through damage to the surrounding tobacco. Swelled stems can be reduced by holding temperatures high (165oF) until the stem is dried. Some
curing barns have areas of ineffective ventilation that contribute to swelled stems. Care should be taken to pack containers uniformly to ensure uniform distribution of curing air.
Scorched
This condition is associated with high temperatures, especially during the stem-drying phase. Scorched tobacco has an abnormal aroma and an off-taste when smoked. To keep scorched tobacco to
a minimum, keep dry-bulb temperatures below 165oF.
Ordering
When curing is over and the stems have been killed, the moisture content of the leaves is near zero. At this stage, the leaves and stems are too brittle to handle, so enough moisture must be added to the leaf to bring the moisture content up to about 15 percent. The leaves are then pliable and can be handled easily.
The rate at which to add moisture to the leaf depends mainly on the method selected to add moisture to the barn (OR CHAMBER) and on the condition of the tobacco itself. A barn of 3,000 pounds cured tobacco requires about 50 gallons of water to bring the leaf into order. Running the fan with the dampers wide open usually brings the tobacco in order overnight. There are many spray-injection systems that can bring a barn of tobacco in order in a few hours. If there is a floor in the curing barn, water can be poured onto the floor. No matter which method is selected, do not apply the water directly to the leaf. The ordering method depends on the equipment available and how quickly you need to get the tobacco in order.
The best time to add moisture back into tobacco is when the leaf temperature is high (165F). The following bit about a nozzle is cool, but I just stick a pan of water on my griddle in the chamber.
Turn the furnace off and insert a hollow cone spray nozzle operating at 100 psi (if possible) into the air stream around the furnace. Using this method, a cured barn of tobacco can be made easy to handle in one to two hours. Table 1 lists different types of hollow cone nozzles and hours of operation to add moisture to cured tobacco.)
Appendix A or you can use my method to make a Wet / Dry Bulb Set-Up
http://wholeleaftobaccollc.com/foru...mometer-Set-Up-on-the-CHEAP&p=49765#post49765
Appendix A
How to Make a Wet-Bulb Thermometer
Proper management of the curing process and proper barn maintenance can reduce fuel usage drastically. No matter what type of bulk barn is used, fuel consumption can be reduced by tightening up
the barn and using a wet-bulb thermometer to gauge ventilation. Caulking compound for structural cracks and new weather stripping for doors cost a small amount compared to the heat they save. You
can make a wet-bulb thermometer for $3.00 to $5.00. The homemade wet-bulb thermometer shown in this photograph has been used successfully as an indicator of wet-bulb temperature in bulk barns.
Materials
2 - pieces 1” PVC pipe, 7” long (one piece with 1/4” hole
drilled 1 1/2” from one end)
1 - piece 1” PVC pipe, 2” long
2 - 90o 1” PVC elbows
2 - end caps, 1” PVC
1 - piece athletic shoestring, 7” long (wick)
1 - Tobacco Curing Thermometer with bulb guards cut out
1 - wide rubber band
1 - piece of thread (not shown) 4” long to tie wick to
thermometer bulb
Instructions for Construction, Filling and Using
1. Glue all PVC pipe together as shown in the figure.
2. Carefully remove glass thermometer bulb from holder
and cut out in a 1 to 1 1/2” square around the bulb.
3. Replace glass thermometer bulb and calibrate according to another thermometer.
4. Secure thermometer to PVC pipe with rubber band or light gauge wire.
5. Fill with water. A large syringe or a small snout
“squeeze-it”-type plastic detergent bottle may be helpful.
6. Insert wick into water. A small nail, large toothpick or kitchen matchstick may be helpful.
7. Place in curing barn where air flow is strong. In up-draft barns (e.g., Roanoke, Long, Powell),
lay wet-bulb device flat on its back on the perforated floor near the loading doors. In down-draft
barns (e.g., bulk tobacco), lay wet-bulb device flat on its back near the loading doors where air
flow will strike the wet bulb of the thermometer.
8. Open fresh air vents only enough to maintain a wet-bulb temperature of 100o to 105oF during leaf drying and 105o to 110oF during stem drying.
The finished product
I think I got it all here and is right...
Hope I don't get into trouble for this post - Happy Curing of Your Baccy Crops.
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