Yeast cells: the smaller ones are daughter cells, recently budded off from the larger ones, which display budding scars
There are some questions I consistently get asked, year after year. For instance, it's a pretty good bet that few men get asked about yeast quite as much as I do. Come to think of it, it's probably not a distinction anyone would aspire to, unless they were a preeminent baker, or a microbiologist specialising in fungi.
However, if a winemaker doesn't eventually get a fair understanding of yeast and how it works, they're not going to be able to consistently produce drinkable wine, much less deliciously wonderful wine.
By far the two most common questions about wine in kits are in regards to substitution and rehydrating. First, people often wonder if they can exchange different yeasts for the ones we include. The answer is, “Probably--but it depends.”
This isn't as unhelpful as it sounds. We do a lot of testing of different strains of yeast with different kit formulations. So kit makers do need to keep in mind that we choose one strain rather than another, for each kit, for specific reasons. Some of the factors in each choice include whether the yeast allows quick and complete fermentation before bottling, and whether or not it will settle out afterwards. And the primary consideration is whether the yeast will be able to handle pasteurized juice, which has sugar bonds that are harder to break. If the yeast can't “crack” the death grip of these bonds your wine is going to have a distinct 'candy' taste that won't age out or improve with time.
So anyone wanting to substitute their preferred yeast strain in a kit can feel free to experiment, especially if they're confident it will meet all those conditions. But a yeast that allows a beautiful expression of varietal character in wine made straight from grapes may perform less well in a kit. So this substitution should follow a lot of research into the yeast manufacturer's literature.
And speaking of literature, another common question is prompted by the yeast packages we put into the kits. Many include instructions from the manufacturer, recommending that the yeast be rehydrated before it's put into the fermenter. But we tell you just to sprinkle it on without doing that. So who's right?
Another unhelpful answer: Both. To rehydrate, you'd need a very precise amount of water per grams of yeast, and it would need to be in a precise, quite narrow temperature range. Mistakes in either of those would ruin the rehydration. While it's true that using that method technically gives the largest number of live yeast cells, yeast used with the sprinkling method never seems to suffer from a lack. There are more than sufficient live cells to accomplish a complete fermentation.
There's some room for variation in the kinds of yeast used in kits, and in how you prepare and introduce it to the juice. But you might want to wait until you've had experience with a few kits first, and then make small changes and write down the results. It's hard to imagine that something so small and apparently simple could have such drastic effects on how a wine turns out, but yeast has the most significant effect of any ingredient in our kits.