Rehydrating yeast?

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Handy Turnip

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I have only done wine kits to date, and the ones I've done generally have instructions to sprinkle the yeast packet on top of the juice and let it go. And this has worked to date with no issues.

However I notice that lots of people talk about rehydrating yeast, and I even think the instructions on the back of the packets supplied with the kits talk about rehydrating them.

So how come they don't need rehydrating when doing the kits? Just curious!
 

JeffA

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Mostly rehydrating the yeast speeds up the fermentation reaction time (makes it start quicker). However, rehydrating the yeast first also has some benefit to having less of a shock to the yeast. Makes them happy as it was told to me once. And best results come from happy yeast. Another good use of rehydrating yeast first for the home wine make is if you make wine from store bought juices. Some of these juices have preservatives in them, which will prevent your yeast from doing their job. Rehydrating the yeast first gives them a more fighting chance.
 

Rice_Guy

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* dry yeast has had a lot of cellular damage in removing water and has limited glycogen reserves to start them budding
* yeast are grown in a chemical cell culture which does not have the stressors a natural fruit must might have (ex pH, mineral variation, type of sugar). A rehydration protocol is intended reduce shock and introduce the yeast to the makeup of the must
* as @JeffA said having a high population of cells allows the yeast to out compete bacteria and other contaminants that naturally occur on fresh fruit
* yeast do best at just under 110F, a rehydration protocol tempers the yeast to must temperature roughly 15 degrees every fifteen minutes.
* rehydrated yeast should be mixed in the tank to minimize the risk of localized contaminants getting a foot hold in a portion of the tank

in the scheme of things the six gallon home winery can get away with sprinkling the yeast since mixing dynamics are better on six gallons than a thousand gallon tank. It is well worth while rehydrating the yeast if it is a high stress to yeast must as honey or cranberry, but for a grape must it is chemically/ sugar wise pretty good so we can get away with without rehydration.
I sprinkle on the surface too. Possibly I’ve been lucky.
 

Handy Turnip

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Cheers all, really interesting to know. I'll continue to sprinkle as it's worked fine to date.
 

Jovimaple

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I always have sprinkled except when I started my first DB the other day. I followed the instructions in the recipe and also had an epiphany and realized I could use a meat thermometer to measure the temp of my water exactly. It worked great! In my past experience of trying to start yeast for bread, I never had good luck. I think "warm water" is too subjective, but I can definitely do 100 degrees! For kits, I will follow the directions, but for my other wines, I think I may rehydrate them from now on.
 

winemaker81

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I followed the instructions in the recipe and also had an epiphany and realized I could use a meat thermometer to measure the temp of my water exactly.
+1!! I purchased an inexpensive digital thermometer last year and find it works great for testing hydration water and must temperature.
 
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