This is a question that is raised often. Tim Vandergrift (Tech Svcs
Mgr at WinExpert) has answered this in other forums, as the WinExpert
kits are among those that recommend just sprinkling. Basically, his
response is that, yes, if you follow the rehydration instructions very
carefully, as to temperature and timing, you will get the greatest
amount of active yeast in a short period of time. However, those
instructions must be followed very carefully. If the water is too hot
or too cold, you won't get good results. If you wait too long after
rehydration, or not long enough, you won't get good results. The
experience of the kit makers is that too many customers just don't
follow the directions closely enough to get consistently good results.
On the other hand, sprinkling the yeast on the surface and letting it
rehydrate at its own pace works very nearly as well, with much less
effort. Even using the sprinkle technique, you can stir the wine after
the initial rehydration period (starting, say, a day after sprinkling).
You just don't want to stir in the yeast immediately, as the yeast
takes time to acclimate itself to the new environment.

So if you're willing to measure the water temp. with a thermometer and
follow the rehydration instructions precisely, go ahead and do that.
Personally, I'm lazy; if I'm using one of the mainstream wine yeast
strains (say, Premier Cuvee, or EC-1118), I just sprinkle, cover
loosely and walk away. I've done 30 or 40 kits that way, as well as
fruit wines, and some from fresh grapes. Never had a problem with it.


Doug