Whole Leaf Tobacco

Yellowing Phase

ChinaVoodoo

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It is pretty consistent that flue curing schedules include a yellowing phase between 90°F and 110°F. Is the sole purpose of this to gain colour consistency within all the leaves in a batch, or is there some other reason?

I ask because a lot of people pile at ambient temperature until yellow, then jump strait into the higher temperature stages.
 

deluxestogie

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Gist: Faster yellowing = sweeter finished leaf.

Yellowing phase, in the chart that I use, is held at 100°F. I try to hold it between 96°F and 102°F. Natural sugars within any variety leaf (maple, tobacco, etc.) are slowly consumed in a separate process, which is at a fairly steady rate, so long as the lamina remain alive. As the chlorophyll breaks down, the already present xanthophylls and carotenoids reveal the yellow to orange color that has been masked by the chlorophyll. Yellowing at 100°F is an attempt to accelerate the breakdown of chlorophyll, while reducing the time during which background metabolism within the leaf is consuming sugars and other carbs--a consumption that continues until the leaf is dead. My understanding is that the added heat accelerates chlorophyll breakdown more than it accelerates the metabolism of sugars. That would imply that longer duration yellowing would lead to less sugar retained in the finished leaf.

Temps above 104°F (if I recall correctly) accelerate leaf death, and is not an intended part of the yellowing phase. Some members have been quite happy with results from yellowing at higher temperatures.

Bob
 

plantdude

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As a spin off from the question, what are some thoughts about yellowing before sun curing?
 
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