Taming the Yeast Beast
We spend a lot of time thinking about yeast--unless someone is a professional baker they probably don't think about yeast very much at all, but as a winemaker, you need a good feel for how your yeast is going to work. Without it you won't get wine, just sweet grape juice--and that's no fun at all.
The most common question winemakers with a few wine kits under their belt ask come from reading a wine yeast company's website. The descriptions make it sound like you could make even better wine if you switched out the plain yeast for something with more flavor. The question is how it's going to affect the kit (other than making it even more awesome), and should you do it.
The answer is, “It depends.”
That sounds unhelpful, but the question is open-ended: there are dozens of strains of winemaking yeast available to home vintners, and hundreds more lurking in wineries and in specialty companies vaults, so understanding how each one is going to affect the kit is a big task.
It helps to think about how we choose the yeast for kits. We have almost every strain of yeast available to us, and there are a number of criteria a yeast has to meet to make the grade.
First, it needs to start fast and to complete fermentation quickly. Fining and stabilizing can happen until the yeast is finished eating all the sugar, and in addition slow starters can allow spoilage organisms to take hold and change the character or even spoil the wine. Yeast that dawdle to the finish extend kit timelines unpredictably, so that strikes a bunch of them off of the list
Second, can the yeast will ferment pasteurized juice? Pasteurizing sort-of binds up the naturally occurring sugar in the juice, making it hard for yeast to ferment fully. If the yeast strain doesn't have the enzyme activity to break these bonds, a certain amount of sugar just isn't going to ferment and the wine will taste sweeter than it should.
Third, and of equal importance to the first two, the yeast needs to express the best characteristics of the grapes used in the kit. We do dozens of yeast trials--it's been observed (correctly) that kits tend to use an awful lot of the same yeast strain, Prise de Mousse, either in the form of EC 1118 or another proprietary name. That's not because it's cheaper or generic, it's because it can make the kit taste great, while fermenting quickly and thoroughly. If there was another yeast that did all these things better we would (and we do!) use it in the kits that it excelled in.
If you want to substitute yeast in your kit you should understand that we already tried that strain in our kit and rejected it for not fulfilling one or more of the three criteria above. If you're willing to gamble a little, and are comfortable with extended timelines and making clearing and fining decisions without the benefit of the instructions, you can give it a shot. You won't spoil your kit (that's actually pretty hard to do) but it may not deliver the character described in the literature. Whether that turns out to be a good thing or a bad one . . . you'll be the one who decides when you taste it.