The way most white grapes are processed on the crushpad is quite different than the way red grapes are processed. In this installment of the Harvest Series, I’ll talk about white grapes and how they’re turned into wine.
Once the grapes arrive at the winery’s crushpad, they are destemmed (if they haven’t been machine picked), crushed, and sorted by a crusher/destemmer machine. The more modern machines need little human sorting, but the goal is to remove as much MOG (material other than grapes) as possible. The picking bins are emptied onto a conveyer belt or into a hopper that leads to the destemmer. The destemmer rotates at a high rate of speed to remove the berries from the stems. The berries then get crushed as much or as little as the winemaker wants between rubber rollers that drop the berries onto a sorting or shaker table. A sorting table will merely carry the berries past workers who then sort out sticks, leaves, rocks, etc. from the grapes. A shaker table will vibrate all of these things into a separate output area from the berries, and require little human assistance. If you’ve really got a lot of money to invest in equipment, then you can get an optical sensor sorter, which “sees” MOG and uses pinpoint-focused air jets to blast it away from the berries. Whatever the method, the point is to have a clean product for fermentation.
Once the grapes are through the destemmer/crusher/sorter, they go straight into a press. Most modern presses are hydraulic and use an internal bladder to gently press the grapes against the perforated side of the main compartment, keeping the skins and seeds from getting into the juice being collected below. Whole clusters can also be pressed without being separated from the stems, but the grapes should be relatively free of MOG if you do this. Once the juice has been pressed out, the skins (now called pomace) are dumped out of the press and discarded and the juice is pumped to a chilled tank. If a winemaker is making an “orange wine” or just wants more color or body from the skins, they will choose to leave the skins and juice soaking together for at least a day before pressing, but most white wines are not made this way.
Once the juice is in a tank chilled to about 40℉ (4.4℃), it will sit overnight so that all solids can settle to the bottom. Keeping it below refrigeration temperature will prevent natural yeasts from starting fermentation and help the solids to settle faster. The clearer juice will be racked to another chilled tank the next day and specially selected yeast will be added to start fermentation. A cool fermentation will result in a fresher, cleaner wine with more aromatics. If the fermentation is not temperature-controlled, you will end up with a wine that has more cooked or bruised fruit aromas and flavors that overtake any floral or mineral characteristics, and will appear more oxidized. This is especially important for white wines, as they are more sensitive to light and oxygen than red wines.
A cool fermentation usually takes about 3 weeks to finish. Once finished, the wine will be transferred to barrels for aging, or racked off of the spent yeast cells and solids and prepared for bottling if it is an unoaked style. To see how red grapes are processed, tune in for the fourth installment next week.