Grape juice is in fermentation vessel—usually stainless steel, but wood or concrete also is used. Yeast decisions are made. More decisions for the wine maker.
How do you manage fermentation? During red wine fermentation, a crust or pad—the must—forms on the top of your fermentation vessel. To extract flavors you worked hard in the vineyard to create, you need to expose fermenting juice to all elements of your juice.
You can use mechanical pumps to pump juice from the bottom of the vessel to pour on top of the cap. The process submerges grape skins in juice and brings carbon dioxide to the surface. “Pump overs” (“remontage” in French) aggressively extract lots of flavor. Makes for rich red wines.
“Punch downs” are done manually using tool roughly resembling a ski pole. Punch downs extract flavors more delicately, make for more subtle red wines.
Fermentation can be completed in a week or two. At some point, conversion of sugar to alcohol exceeds 16%, killing the yeast. If temperature is controlled, fermentation can take longer. Vin Santo, an Italian dessert wine made from white grapes, and amarone, a rich red wine made from partially dried grapes, can take from 50 days to four years to ferment.
In addition to pump and punch, free run and pressing are other winemaker decisions. Free run, as name implies, is juice that flows freely after grapes split under their own weight. Free run is considered the highest quality in white wines since it has the least contact with grape skin, seeds, and stems.
Winemakers can get up to 15% more juice by pressing grapes. Classic picture of pressing is stomping barefoot women. Today, pressing usually is done by variety of mechanical means, but pressure on grapes is calculated to be that of a 120-pound woman stomping grapes. Most juice made into wine is free run, extracted during de-stemming. Cheaper wines are pressed more aggressively, resulting in more harshness and bitterness from cracked seeds.
After alcoholic fermentation, a second fermentation—malolactic—can occur. A microbe feasts on wine acids and converts sharp-tasting malic acid into creamier, chocolatey lactic acid. Most red wines undergo malolactic fermentation to smooth things out. White wines undergo malolactic fermentation less often since acidity is prized in whites. Chardonnay is exception, and results in its creamy and buttery notes.
Next week: Aging.
Last round: Inventor of Life Savers made a mint. Joke is funnier after sip of wine.