In Part 1 of her harvest overview, Cathy Corison talked about picking, just after her first harvest of the season. Here she talks about fermentation, just as some of her tanks were beginning the transformation from juice to wine.
"I tend to cold soak for two or three days. Most of us have come to prefer squatty tanks that are as wide as they are tall. Especially with Cabernet you want to optimize skin contact, basically because that's where all the flavor and color is. Because volume goes up as a cube and surface goes up as a square, the squattier the tank the more passive contact you have—the more the skins are in contact even when you're not punching down or pumping over. So it just gives you better ratio of skins in contact with the juice. All of my lots are quite small. My fermentations are seldom over 10 tons, which is a 1,500-gallon tank.
"I use a quarter of a normal inoculum of yeast. It's sort of a hybrid fermentation—partly wild—and I know I've got the guy in there that can finish it. I think there's a complexity that comes with a population fermentation. It's a series, it turns out—a sequence of species in a wild fermentation. Sequential species take over the fermentation because some of them are tolerant of very high sugar, which is very hard on microorganisms, and they do well early. And others are tolerant of the alcohol at the end, but intolerant of the sugar at the beginning. The hardest part for the yeast is the end, when the alcohol is high. So I have [a strain] in there I know can finish it in a healthy way.
"I like to get the ferments good and hot early, because I think all the good stuff comes out early and all the bad stuff comes out late. Alcohol is a very good solvent, so I don't like the ferment to be hot at the end. But I do like plenty of heat for extraction early in the fermentation. [And] we use a very gentle pumping-over. We have a device that basically sprinkles over the cap, and the fermenting must just trickles through it.
"I think we're mostly looking for a clean fermentation, so we're looking for any signs that something might be going awry. The most common issue would be that the yeast would start to provide some hydrogen sulfide, and that's almost always a nutritional issue. So we'll sometimes feed them with yeast extract. That gives them the nutrients to be happy again and stop making hydrogen sulfide.
"We do the brix [a measure of sugar content] a couple times a day during active fermentation, and, of course, we taste it—basically making sure that the fermentation is staying on track. It's at the end that we tend to be critically looking to make decisions, which are mostly tannin-management sorts of things. I choose to macerate part of my wine, and not macerate the other part, because I love what maceration does to the feel of the tannins—it moves them around your mouth and makes them very soft. But like anything in life, you usually lose something when you gain something. With maceration you lose fruit, and fruit is very important to my wines. So I do a combination. The real secret is that these are Rutherford benchland grapes, so the tannins are already very soft—they're never 'ouch' tannins even when they're very young."
Next week, once her ferments have finished, Corison will conclude this series by talking about how her wines are managed once they're in barrels.