Wort gravity and yeast

[jimmyjusa]

I was talking to a local brewer last night and we were talking about different yeasts. At one point it sounded like they just pitch multiple packs of yeast vs making a starter. For a different beer he mentioned a starter so perhaps only the initial pitch is all fresh packs but i didn't ask about the specifics. Anyways, i say that to give the background for where my question originated. I know that for a high gravity brew you can make a small beer first and essentially that is a big starter. Does the wort gravity of this initial beer have any relation to the yeast count that ends up in the yeast cake? (1.035 og vs 1.050 og). Another brewery releases a new 5 gallon batch every week which made me think that would be an easy way to constantly keep yeast at the ready.

 

[Gnomebrewer]

Wort gravity (and alcohol content) affects yeast vitality and viability more than yeast count. Yeast multiply and grow during the initial stages of the ferment, using oxygen and nutrients in the wort. They then consume the sugars, creating alcohol. High sugar (and subsequent high alcohol) content is stressful for yeast, which leads to lower viability. That's why it's often written not to reuse yeast from 1.060 or higher worts (although IMO that's a bit yeast dependent). Yeast will be best for re-use from 1.040 or lower worts (hence why starters are typically 1.030 to 1.040). Worts that are too low in gravity are likely to be lacking in nutrients (which come from grains) so at some point very low gravity worts will also be less desirable for harvesting yeast. When I use a batch of beer as a 'starter' for a higher gravity/larger volume batch, I typically aim for somewhere in the mid 1.040's and use a good hit of yeast nutrient.

Commercial breweries will mostly purchase a batch of yeast big enough for a straight pitch (it must be a small brewery that uses multiple (homebrew?) packs), then reuse slurry for future batches (the number of generations of reuse depends on the brewery but I'd guess is typically around 5 to 8 generations).

 

[jimmyjusa]

Wort gravity (and alcohol content) affects yeast vitality and viability more than yeast count. Yeast multiply and grow during the initial stages of the ferment, using oxygen and nutrients in the wort. They then consume the sugars, creating alcohol. High sugar (and subsequent high alcohol) content is stressful for yeast, which leads to lower viability. That's why it's often written not to reuse yeast from 1.060 or higher worts (although IMO that's a bit yeast dependent). Yeast will be best for re-use from 1.040 or lower worts (hence why starters are typically 1.030 to 1.040). Worts that are too low in gravity are likely to be lacking in nutrients (which come from grains) so at some point very low gravity worts will also be less desirable for harvesting yeast. When I use a batch of beer as a 'starter' for a higher gravity/larger volume batch, I typically aim for somewhere in the mid 1.040's and use a good hit of yeast nutrient.

Commercial breweries will mostly purchase a batch of yeast big enough for a straight pitch (it must be a small brewery that uses multiple (homebrew?) packs), then reuse slurry for future batches (the number of generations of reuse depends on the brewery but I'd guess is typically around 5 to 8 generations).

I think he's doing a 1 barrel system. He said 3 packs was not enough to do it but I'm not sure how much he uses. He said he pitched a 3L slurry on a recent beer.