Another yeast pitch rate question

[mac_1103]

So does that mean those of us that use dry yeast should should all be buying the 500 gram packs of yeast?

I've been pitching one pack into five gallons of medium gravity wort forever and getting good fermentations and good beers. I use two packs for high gravity brews. I'm sure there are plenty of people who would say that we're all underpitching, but if we aren't actually observing any of the ill effects typically associated with underpitching then maybe we aren't actually underpitching.

Or do we assume the yeast makers are hedging their numbers to be safe and telling us a low number of viable yeast when in most cases it's double that or more

Yes. If they say >6 billion cells per gram, then anything over 6.01 billion passes. But if they're routinely packaging >12 billion per gram and decide to make that the specification, then when one batch comes out at 11.9 billion they have to fail it.

 

[hilljack13]

I guess it's time to measure a gram and start counting all those billions!

 

[hotbeer]

Yeah, if one assumes they are understating their cell count to only a 1/3 or 1/4 of what the actual typical count is, then the pitch rates of 1 to 1.5 million cells/ml/degree Plato seems to work out for their recommended dosage of 80 to 120 g/hl and the suggested cell count of Brewfather and Brewer's Friend.

 

[dmtaylor]

Somewhat off-topic yet somewhat related, what is the proper procedure for storing 1/2 to 3/4 of an opened yeast sachet?

I just fold over the corner, tape it, put it in the refrigerator. Lasts pretty much forever.

 

[dmtaylor]

do we assume the yeast makers are hedging their numbers to be safe and telling us a low number of viable yeast when in most cases it's double that or more, but they can't take the liability of getting any one pack being wrong for any of a number of reasons and someone just happening to check the actual count for that pack?

YES, THIS. ^^^^

 

[ncbrewer]

A couple of references:

In How to Brew, E4, Palmer states that "a good rule of thumb is that dry yeast has about 10 billion cells per gram".

Yeast, by Zainasheff and White, states "Most dry yeast contains about 7 billion to 20 billion cells per gram"

Edit: For those who want to read more, the How to Brew reference was from page 109, and there is more discussion in Chapter 7. The Yeast reference was from page 124.