Cold pitching yeast.

[Tummydoc]

A lot of folks suggest you should warm yeast before pitching if previously stored refrigerated. They claim it reduces yeast "shock" and shortens lag time.

I can't find much research that supports this dogma. Many beer forums advocate that cold pitching actually reduces lag time, leads to more vigorous fermentation and increased attenuation.

From the AHB board:  
"The reason for this is the yeast, as they go into dormancy (eg. due to drying, low temp, or lack of food), produce large amounts of sugars. These are stored internally within the cell walls of the yeast as a future energy reserve for when the yeast will eventually exit dormancy when the external environment becomes less hostile (eg. wetter, warmer, or more food about).

 Glycogen is an important sugar that is stored. But another one is trehalose - a molecule of which is made by the bonding of two glucose molecules together. Trehalose is thought to form a supporting gel-like substance in the dormant yeast cells which protects its organelles from getting damaged when the cell distorts due to dehydration, and protection from osmotic pressure when its moved from a dilute environment (eg. a jar of water) to a more concentrated environment (eg. fresh wort).
 
 By letting the jar of washed yeast come up to room temp before pitching, the yeast cells exit dormancy (wake up) and become biologically active again, and this requires an immediate need for energy. It was long thought that it was the sugar glycogen that was first used by the yeast for energy as they came out of dormancy. But it is now understood that the yeast consume the trehalose first - and in doing so the yeast become very vulnerable to the osmotic potential of wort very quickly.
 
 So if you leave the washed yeast to come up to room temp for hours, when you pitch it into the wort much of the yeast's reserves of the protective trehalose are gone and many of the yeast cells will be torn apart by the wort that can invade the cells by osmotic pressure."

Also a post by Dr Clayton Cone of Danstar Yeast in response to a question about cold pitching of yeast:
 
"I have not seen any studies done using this protocol. If I had to take a guess it would be centered around the Trehalose content in the yeast cell. Trehalose seems to be an all around stress related factor. Almost immediately upon the cold storage of the yeast, trehalose begins to build up to help the yeast to adapt to its new environment. Upon pitching this stress factor assists the yeast to adapt to its new environment; warmer temperature and higher osmotic pressure. If the pitching yeast is allowed to warm up for any appreciable time before pitching the carbohydrate reserve, trehalose being one of them will be quickly used up as an energy source. The yeast would then take a longer time adapting to its new environment in the wort thus increasing the lag phase.

Something similar happens when using Active Dry Yeast. The factory builds into each yeast cell an abundance of the stress factor; trehalose. Our recommendations is to rehydrate the yeast in warm water and pitch into the wort (or must) within 30 minutes, because the yeast will begin to metabolize its carbohydrate reserve including trehalose immediately upon reactivation and weaken the yeast if it is not in the presence of a new supply of energy. It will have also used up the stress factor that would have assisted it in adapting to the new osmotic environment. I am sure that there is more to the explanation than I have given."


I found this interesting. I store yeast slurry in my fridge, and usually pitch directly into the mash/wash when temp is appropriate. I was just too lazy or inpatient to warm the yeast or proof it. Interesting that some advocate that as preferred.

 

[seabass]

Imperial yeast says to store and pitch cold. If you aren't making a starter there's no reason to warm it up. I've stopped smacking the smack pack on wyeast and just pitch it cold.

The info on trehalose makes a lot of sense.

[jonnys_spirit]

I usually do a starter with a small mash made on the stove. Pitching the chilled slurry from the fridge in a lower gravity starter. By the time the large mash is cool the starter is making all kinds of CO2. Not sure if that’s similar or not.

Cheers,
Jonny

[Truckinbutch]

I pull a bit of mash when I'm done cooking and pitch a starter in it while I'm transferring mash from my cooker to the fermenter . By the time I have the mash transferred and thinned with cold water , and aireated with a paddle mixer , the starter should be overflowing the quart jar and the mash should have cooled to a reasonable pitching temperature . I dump it . mix a bit , and seal the ferment up . Case closed until the ferment is done and settled .
Try not to make it more complicated than what it is .
Getting a good conversion when you cook is the real magic .

[Odin]

I have done many comparisons and like to keep things simple. Here's what works for me: Create a mash, let it cool down to fermentation temp, take the yeast and sprinkle it on top. It'll sink in slowly. No agitation. Works every time. As simple as it gets.

Odin.

[Tummydoc]

I agree with dried yeast, from fridge to fermenter. With liquid too for me