Well, here we are. Primary fermentation has come and gone. We now begin phase II of the wine making process. Just a quick note, in wine making, fermenting juice is called must. I just want to be clear on that term; otherwise it could seem a bit confusing considering it's alternate meaning. Anyway, once the specific gravity of the must reaches between 0.20 and 0.15 it's time to place the must under airlock. The must will usually reach this point after about 5 days in primary fermentation at a temperature of 70 degrees. The vigor of primary fermentation will begin to slow at this point as the alcohol level beings to reach about 12% or just above complete dryness. This is when the must is ready to begin an anaerobic fermentation. I usually like to strain the large solids off the must at this phase. You do not filter the must - you're simply trying to remove large pieces of skin and hulls so racking the wine is easier later and clean up less of a hassle. The yeast and smaller bits must be allowed to pass into the carboy or you will likely end up with a stuck fermentation.
Once the must is transfered to the carboy and the solids and yeast begin to settle, the must will begin giving off gas at a rapid rate. In fact it will seem like the must has gotten a second wind. You'll notice the airlock will be releasing air approximately every second within only a few hours. I have to emphasize, it is not a good idea to top the carboy up to the top as about an inch of foam will form initially. Besides, it isn't necessary to top up now, as there is no concern at this stage of exposure to air (oxidation) since the air will be forced out of the vessle once the airlock is fitted and gases begin releasing. That said, it is important not to remove the airlock for about the next four weeks, or until secondary fermentation begins to slow to the point where bubbles are escaping only about every 20-30 seconds from the airlock.
So, secondary fermentation will continue for about the next four weeks. Check back to see how this years hand picked blueberry wine goes from the field to the bottle.