This is probably my favorite part of the process (next to drinking the finished wine). This is the barrel of the press and the nylon pressing bag. The bag is a fine mesh and serves as a strainer, keeping the seeds, skins, and larger particles out of the wine. Before pouring the must into the press, I remove the cap and temporally place it in a sterile jug. This speeds up the pressing by letting me pour the liquid part of the must first.
I then take the liquid and slowly pour it though the pressing bag.
After the liquid portion of the must is poured thru, the solids are then placed into the pressing bag, the bag is then rolled closed, and the pressing disk is placed on top.
The "must" is then pressed. The press is homemade and made of rock maple and stainless steel with oak supports underneath. A hydraulic bottle jack supplies the pressure. I usually press until the flow slows down and then release the pressure, break up the cake, and press again, repeating this for about three cycles.
Initially, there was about 100 lbs of grapes (stems, etc). The must is still fermenting at this point and the brix is now down to about 3 (3% sugar). The yield was about 6 gallons of free run juice and another 2.5 gallons by pressing the skins and seeds for a total of 8.5 gallons.
After pressing, the new wine is placed into glass carboys that are sealed with water locks. At this point, the fermentation goes from aerobic (consuming oxygen) to anaerobic. You can already see the remaining solids starting to settle out. In a few weeks, the wine will start to clear. The jugs are placed in a cool place for about 2-3 months. During that time, the ambient temperature may drop below freezing causing the wine to precipitate out excess acid in the form of tartrates. In certain cases, chalk (calcium carbonate) may be added to force a decrease in acid. It is virtually never needed in wines of this type, but an interesting byproduct of this reaction (naturally occuring tartaric acid + calcium carbonate) is the precipation of calcium bitartrate...better known as "cream of tartar"...the stuff used to stiffen eggwhites in cooking.
These are the solid remains of the original 100 lbs. sitting on a pizza box. They are almost dry and actually will fall apart when picked up. It is possible to make a "second" wine out of it by adding water and sugar and letting it ferment again, however the quality will not be very good. This pile actually went into my garden as fertilizer.