Yeast Cleanup

New to brewing and love every minute of it!! I've experienced every beginner brewer mistake and I'm pretty sure I've invented a few new mistakes.

That aside, now that I'm able to repeatedly make "good beer", I'm ready to begin adding a little finesse to my process...

I notice some recipes indicate one temperature for say, two thirds of the fermentation and then slowly raise the fermentation to some other temperature for the final third of the fermentation. The comments most likely to follow that scheme is "to allow the yeast to complete a clean up".

As a beginner, that brings up a couple of questions:

1) What is meant by "yeast cleanup"?

2) Is yeast cleanup associated with certain "beer styles"?

3) or is yeast cleanup used to improve a less than ideal fermentation?

Thanks!

HomeBrewTalk is AWESOME!

 

There are various compounds the yeast produce during fermentation that they will go back and consume later, after most of the rest of their food is gone. Two of the most common are acetaldehyde and diacetyl.

Acetaldehyde tastes like green apples, at least according to some people. To me, it has the bite orange juice gets when it starts to turn. Acetaldehyde leads to a 'green beer' or 'young beer' flavor. Taking the beer off the yeast too early can lead to acetaldehyde in the final product.

Diacetyl tastes like artificial butter in strong enough concentrations. Sometimes it can be picked up in low quantities as a muddy sweetness, or as a slick feeling in your mouth. Some yeasts are more prone to produce diacetyl than others. Most of the lager yeasts and some of the British ale yeasts are known for diacetyl. These are the beers where you want to raise temps toward the end of fermentation.

If you had a poor fermentation, raising temps and leaving the beer on the cake longer is not likely to dramatically improve the end result.

 

OK that makes sense. Thanks for that informative reply.

Would *you* tend to always use this technique or only for certain yeasts?

 

Oops. I see you did answer my original questions.
Sorry about that.

 

It depends on the yeast. Lager yeasts, always. Same with 1968/WLP002.

With American ale yeast, I don't worry about it. With weizen yeast, and at least some Belgian strains, I raise temps toward the end of fermentation, but that's more because I don't want them to stop early than because of concerns about diacetyl.

 

Thanks again!

I love learning this stuff.

 

to take a step back from jeffjms reply, this is sort of how i understand yeast activity

1- the higher the temperature, the more active the yeast. for example, the same beer will ferment 4-5 times faster at 75 degrees than at 58 degrees.

2- after high krausen, as the gravity of the beer gets lower and lower, fewer and fewer yeast will be in suspension.

3 - the more yeast in suspension, the more the yeast can reduce fermentation byproducts along with any remaining sugars

so, if we want to reduce fermentation by-products, we want as many yeast in suspension as possible. so to accomplish this, we ramp up temps at the end to try to keep them in suspension.

of course we should try to reduce them in the first place, since we know not all kinds of fermentation byproducts are cleaned up. and some only to a degree. to reduce these things, we try to use plenty of oxygen, watch temperatures, and not pitch too few yeast.