Figure about five pounds of fruit for each gallon of wine. A six gallon glass carbon jug will make two cases of wine, a three gallon one will make a case. So for a 5-6 gallon recipe take 20 lbs or blackberries and put them in two 5
gallon food-grade plastic buckets. Split the blackberries into two halves and put each half into the plastic buckets. These will be your primary fermenters. Smash the fruit. Add water so that the total volume between the two buckets is about 7-8 gallons. Like JBD said you'll want to get a hydrometer. They won't cost much at a beer and winemaking store. Take a cup or so of the juice out and test the specific gravity with the hydrometer.
Unless you are making wine from wine grapes you will have to add sugar. For a sweet wine, shoot for a specific gravity about 1170 to 1130-1135. If this sugar got all fermented out you would have an alcohol percentage of 18%. Most yeasts can't ferment that high, so the I fermented sugar will give you your sweet wine. If you want more sweetness at the end you can always add more sugar at the end once the alcohol is high enough to prevent any more fermentation.
Next crush the fruit and sugar mixture and test the specific gravity again with the hygrometer. Make any adjustments either by adding water or sugar. Add in some potassium metabisulphite which you can get in any homebrewing and winemaking store. Cover and let sit overnight for 24 hours. This kills the wild yeasts and bacteria on the fruit. Then add a packer of wine yeast. A good all purpose yeast is Champagne yeast which ferments out to the highest alcohol rate of any yeast and has a clean, neutral flavor. But any red wine yeast will do fine. These are
cheap and can aslo be obtained and a wine and beer aming store. Just don't use bread or beer yeast.
Cover the buckets with a clean towel and either tie it on the bucket with a big rubber band or just place a plate on top of it. Within a day it will start foaming. Twice a day "punch the cap" and stir. This gets the fruit solids that float to the top mixed back in. It also aerates the "must" which is important at tthis early,
"primary" stage of fermentation.
After 3 or 4 or 5 days, the fermentation will slow down and it will be time for secondary fermentation which will take place in the 6 gallon glass carboy jug. Squeeze out the fruit solids and seems using a filter bag or cloth of some kind or a wine press if you have one. Place the liquid in the carboy with a stopper with a hole in it and fit a fermentation lock in the stopper. All these things can also be bought at one of those stores. The fermentation lock will let carbon dioxide gas out and no oxygen or contaminants (vinegars cultures for example) in. If you have excess liquid it's good to use a gallon jug to ferment that. That will give you extra to top out the main fermentation jug after syphoning.
When the fermentation crawls to a slow place and a bunch of sediment is at the bottom of the jug a week or so) it's time for the first racking (syphoning). Buy some clear plastic hose at a hardware or at the winemaking store. I also like to have a glass syphoning tube that has a little bowl you can put on the end that can be inserted into the hose. The idea is to syphon the liquid off the sediment into another carboy. Put the fermentation lock on the new carboy and let ferment slowly for a couple of month, then rack again. Here is where you will need extra to top off after each racking because you will lose volume from the sediment.
After the second racking let it sit for three months and rack again, let sit for three months more, then bottle. With each racking there will be less sediment. You want your end product to be clear, not cloudy.
It was awful. But my buddies wine is sweetened just enough so that it's kind of a sweet and sour kind of taste like the good bought wine. I really like it. You can taste the fruit or berries without the taste being overpowered by the sweetness. You actually just add sugar to taste, so you'll just add sugar till you like it.
