Harvest Series Blog 4 --- Processing Red Grapes

Red grapes are processed a bit differently than white grapes, and the biggest difference is when the skins are pressed off of the juice or wine.

Once the grapes arrive at the crushpad, they are sent through a destemming machine (unless they have been machine harvested, in which case they will already be destemmed).  The grapes are sent through rubber rollers which crush or break the skins to the winemaker’s specifications.  They are then sent through either a shaker table or a sorting table to remove any MOG (materials other than grapes).  The grapes are then sent to either a temperature-controlled tank or fermenting bins (basically these are the same ½-1 ton open-top plastic bins that are using for picking, washed and ready to be refilled with processed grapes).  

As temperature is very important during fermentation, and will result in different styles of wine, usually a tank that can be chilled down is used for fermentation of red grapes, depending on what the winemaker is trying to accomplish.  If not controlled, the temperature can get into the 32℃-37℃ range, which will result in big, extracted flavors and pigmentation, and can even cross over into cooked or bruised fruit characteristics; whereas a lower temperature fermentation will result in brighter fruit and floral characteristics and less pigmentation.  If a chilled tank is not available or is not desired, open-top bins are usually used and fermentation will happen in a cool room to minimize heat.

The must (grape skins, seeds, and juice together) will be allowed to sit overnight in what is called a cold-soak.  A cold-soak can be just one day, or it can be several days, as long as the natural yeasts do not start fermentation early.  A cold-soak is done to allow enzymes to break down the skins and pulp, and release more tannin, pigment, and anthocyanins (antioxidants) into the juice.  Once the winemaker has decided that the cold-soak is over, specially chosen yeast will be pitched.  Some winemakers choose to allow the natural yeasts that are on the grapes ferment the wine, but this can be tricky as it will not be as controlled a fermentation as with cultured yeast.  At this time, some winemakers will also add malo-lactic bacteria to the must.  ML bacteria converts the more harsh-tasting malic acid in the grapes to the smoother lactic acid, which helps mouthfeel.  

During red wine fermentation, the must is either punched-down (if fermented in open-top bins) or pumped-over (if in tank) at least a couple times a day.  A punch-down is done with a tool that can be used to push the cap (skins that are floating on top of the juice) back down into the juice.  A pump-over is done by hooking up a pump the tank of fermenting must so that the must can be circulated and sprayed over the top of the cap, which wets and submerges the cap.  This is done because must is not just clean juice, as with white wine, and since skins float to the top during fermentation, they can start to mold if not kept wet with juice.  Also, not as much color or body from the skins will be allowed to permeate into the finished wine if the cap is not submerged as much as possible.  It also disperses heat trapped under the cap, and mixes oxygen into the must, which is necessary for the yeast to survive until fermentation is complete.

Once fermentation is complete (about 7-14 days), the wine and skins are pressed, and the pressed off skins (called pomace) are discarded.  The wine is pumped immediately to tank so that solids and spent yeast cells can settle out.  The wine can stay in tank until the cellar crew is ready to put it to barrel (called barrelling down).  At that time, just the cleaner, more clear wine is pumped off of the solids as it goes into barrel (a process called racking), and the solids are discarded.  This is the beginning of barrel aging.

Stay tuned for the next installment, where I will talk about processing grapes for making rosé.