Taxovich
Member
You should always rehydrate yeast in water. John Palmer: "Often the concentration of sugars in wort is high enough that the yeast can not draw enough water across the cell membranes to restart their metabolism." I'm not going to look up a cite for how osmosis works, but the tl/dr is this: rehydrating properly (with warm water) will give you much more viable yeast than sprinkling the yeast directly on the wort. This would be especially important if you are dealing with a high-gravity wort (like RIS).