If you look at the instructions in your wine kit, they will likely instruct you to sprinkle your packet of dry yeast directly into your must. Yet, if you read the yeast package, (and many textbooks or online) they recommend rehydrating the yeast. Which technique is best? The catch is…rehydration has to be done precisely!
Lalvin EC1118 champagne yeast, for instance, asks you to add the yeast to 10 times its weight in water at 40 to 43 degrees C. Adding the right amount of water is important if you are trying the maximize live cell counts. That’s because the yeast is dried on a substrate of nutrients and sugars. If too little water is used, the yeast will only grow sluggishly. If too much water is used, the cells may burst from the flood of liquid forced across their cell membranes.
Secondly, the temperature range is inflexible. The outer layers of the yeast cells soften best in warm water, If the water isn’t warm enough, the cell won’t soften. If it’s too warm, generally anywhere above 52 degrees C, the yeast cell will cook and die.
The next thing you have to worry about is temperature shear. Yeast is very sensitive to environmental conditions. If they change too quickly from a favourable temperature to a less favourable one, weakened cells may die and others may go dormant in an attempt to ride out the temperature shift. This reduces the number of live, viable cells available to ferment the must, and gives spoilage organisms a chance to get a foothold and potentially ruin your wine.
Given this information, you may think that simply dumping the yeast on top of the must should result in lower cell counts. Evidence shows that this isn’t the case, however; the yeast appears to know what they’re doing. Generally, a 5-gram packet will have less than a six-hour lag phase. This is perfectly acceptable and isn’t long enough to allow spoilage organisms to get a foothold in your wine. Plus, it’s a heck of a lot simpler than going through the rehydrating process, fraught as it is with risks.
The Home Vintner always recommends tearing open the yeast package and sprinkling it on top of your must. Spend the extra time sampling your last batch!
(excerpt from Tim Vandergrift’s wine blog)