Yeast attenuation & clean up

[Prymal]

I have been reading and observing fermentation and have a few thoughts in my head that I want to confirm. As the bulk of fermentation comes to an end the chance of off flavors from a warm fermentation lowers. Also yeast attenuates more at higher temperatures. So it seems that if you start a fermentation at 62 for example let it go for about a week then raise to 70 you could promote slightly further attenuation without worrying about off flavors. Is this true, and if so is it a practice that anyone adheres too?

 

[TimTrone]

I have been reading and observing fermentation and have a few thoughts in my head that I want to confirm. As the bulk of fermentation comes to an end the chance of off flavors from a warm fermentation lowers. Also yeast attenuates more at higher temperatures. So it seems that if you start a fermentation at 62 for example let it go for about a week then raise to 70 you could promote slightly further attenuation without worrying about off flavors. Is this true, and if so is it a practice that anyone adheres too?

It depends a lot on what strain you are using, but for the most part that's correct. I start fermentation on most ales at 58 and throughout a week or so I will let it rise to 65. The first few days of fermentation are the most important.

 

[frozt]

Maybe someone else can weigh in on this, but my understanding is that, barring a stuck fermentation, the yeast will attenuate as much as it will regardless of temp for a given level of fermentable sugars in the wort. In other words, as long as temp is high enough that the yeast don't go dormant and pitching rates are good, you can trust that they'll eat what fermentables are available.

Maybe what you were thinking of regarding temperature vs. attenutation was regarding mash temp (higher mash temp -> lower atten., lower mash temp -> higher atten.)?

Again, maybe someone else will correct me on this, but that is my understanding of the subject.

 

[bob3000]

Its standard practice to raise temp a few degrees at the end of fermentation to keep yeast in suspension to finish the job.

 

[maida7]

Yes I always start cool to control off flavors (esters, harsh alcohol, diacytel acetaldehyde, etc..) Then finish warm to get full attenuation and allow the yeast to clean up any diacytle and acetaldehyde that was produced earlier during the ferment.

Each yeast is different but this is a general out line to follow.

 

[ReverseApacheMaster]

Raising the temperature can sometimes improve attenuation. If the yeast have hit their limits it doesn't matter how warm you make it, but often you can score a few extra points with warmth and a little rousing. Belgian and French strains tend to want to go warmer and keep working and many Belgian and French breweries let their beers go into the 80s (or even the 90s) by the end of fermentation to fully attenuate a beer. Aside from those strains you should obtain full attenuation 99% of the time just by pitching the correct volume of yeast. For your basic American or British strains if you are having to raise the temperature to ferment out a beer you probably underpitched or fermented way too cool to begin with.

 

[Piratwolf]

my understanding is that, barring a stuck fermentation, the yeast will attenuate as much as it will regardless of temp for a given level of fermentable sugars in the wort....

I can't speak from personal scientific experiments, but I can report what I heard yesterday from JZ on an old podcast: his experiments showed that taking Chico yeast down to 60-62 meant a few points less in attenuation.

That suggests to me that there are variations in attenuation at the extreme ends of the recommended range.

 

[badhabit]

For me this becomes a part of the secondary or no secondary question.

 

[Piratwolf]

For me this becomes a part of the secondary or no secondary question.

How? I raise the temp in primary.

 

[maida7]

How? I raise the temp in primary.

If you do your primary right there is no need for a secondary from the yeast performance point of view

 

[Piratwolf]

If you do your primary right there is no need for a secondary from the yeast performance point of view

My point exactly. I also think that secondary is exactly the opposite of what the OP would want as it removes the very yeast that are taking back up the undesirable products they produced.

 

[badhabit]

I am just saying that if you are going to raise your temp do so with as little available and viable yeast as possible. The point is that if the higher temp was avoided to avoid off flavors early in the fermentation then why does that change just because the most active fermentation is complete. If you still have that beer sitting on a half gal of yeast, what is to stop at least some of that yeast from attempting to work just like it did early in the process. I think that if you look at styles, particularly Belgian, that use the temp increase they also want more ester production in the final product.

 

[maida7]

I am just saying that if you are going to raise your temp do so with as little available and viable yeast as possible. The point is that if the higher temp was avoided to avoid off flavors early in the fermentation then why does that change just because the most active fermentation is complete. If you still have that beer sitting on a half gal of yeast, what is to stop at least some of that yeast from attempting to work just like it did early in the process. I think that if you look at styles, particularly Belgian, that use the temp increase they also want more ester production in the final product.

you raise the temp to keep the yeast active and working. At the end of the ferment they will slow down unless you raise the temp. Swirling the fermenter can help also to get them back up into solution again. It will not effect ester production at that stage in the ferment. But it will clean up diacytle and acetaldehayde.

If you let the temp fall at the end of the ferment the yeast will perform these tasks MUCH slower. Then you might want a secondary ferment to give it extra time and to reduce the risk of autolysis while you wait for things to improve.

 

[NordeastBrewer77]

I am just saying that if you are going to raise your temp do so with as little available and viable yeast as possible. The point is that if the higher temp was avoided to avoid off flavors early in the fermentation then why does that change just because the most active fermentation is complete. If you still have that beer sitting on a half gal of yeast, what is to stop at least some of that yeast from attempting to work just like it did early in the process. I think that if you look at styles, particularly Belgian, that use the temp increase they also want more ester production in the final product.

The off flavors from high temp fermentation are mainly produced during the reproductive phase and then some are absorbed (eaten by the yeast) after the yeast finished converting the fermentable sugars. The key here is that these compounds are cleaned up by the yeast, so if you remove the beer from the bulk of the yeast (by transferring it to secondary), how can you expect the yeast to do their thing?
You keep the start of fermentation cool to limit ester production (in styles where you want to limit ester production. Beligians aren't one of these styles) The reason why you warm the yeast at the end is so they stay active and fully attenuate the beer and hopefully re-absorb some of the esters. They'd rather go dormant than eat esters and phenols, but if you keep them warm they won't go dormant as quickly.

My $.02, if you pitch enough yeast, and control temps during fermentation, there is really no need to rely on the yeast to 'clean up' since there won't be much, if anything for them to clean up.

 

[badhabit]

The off flavors from high temp fermentation are mainly produced during the reproductive phase and then some are absorbed (eaten by the yeast) after the yeast finished converting the fermentable sugars. The key here is that these compounds are cleaned up by the yeast, so if you remove the beer from the bulk of the yeast (by transferring it to secondary), how can you expect the yeast to do their thing?
You keep the start of fermentation cool to limit ester production (in styles where you want to limit ester production. Beligians aren't one of these styles) The reason why you warm the yeast at the end is so they stay active and fully attenuate the beer and hopefully re-absorb some of the esters. They'd rather go dormant than eat esters and phenols, but if you keep them warm they won't go dormant as quickly.

My $.02, if you pitch enough yeast, and control temps during fermentation, there is really no need to rely on the yeast to 'clean up' since there won't be much, if anything for them to clean up.

This makes the most sense to me. Use enough yeast to start with, control the temp to reduce the off flavors and then get rid of the yeast. The question that this brings to my mind is what is the process at the commercial micro breweries? Do they raise temp at the end of active ferment? Do they hold the beer in fermentation several weeks or just dump the yeast, maybe filter and conditon and carbonate? My understanding is (not a fact,just my understanding) that the ferment is finished in a week or so, cold crashed and sent to bright tanks, without yeast or at least with the vast majority away from the beer, for carbing in a few days at most?????

 

[maida7]

This makes the most sense to me. Use enough yeast to start with, control the temp to reduce the off flavors and then get rid of the yeast. The question that this brings to my mind is what is the process at the commercial micro breweries? Do they raise temp at the end of active ferment? Do they hold the beer in fermentation several weeks or just dump the yeast, maybe filter and conditon and carbonate? My understanding is (not a fact,just my understanding) that the ferment is finished in a week or so, cold crashed and sent to bright tanks, without yeast or at least with the vast majority away from the beer, for carbing in a few days at most?????

Brewery tanks have no heating only cooling. So they pitch cool and allow the yeast activity to raise the temp in the tank. They can use the glycol cooling to keep things from getting out of control but generally once the growth phase has ended they let the fermenters get pretty warm. The pressure in tall fermenters retards ester formation so a commercial brewer can generally ferment a bit warmer then a home brewer without getting really loud yeast character. Once the fermentation slows to a crawl the beer is usually filtered and moved to a bright tank to be carbonated. Time is money so commercial brewers move the beer out of the fermenter as quick as possible. Could be 5-7 days for an ale. If you have a fresh supply of good healthy yeast and your pitch the proper rates your ferments will be much faster and much cleaner.

 

[NordeastBrewer77]

This makes the most sense to me. Use enough yeast to start with, control the temp to reduce the off flavors and then get rid of the yeast. The question that this brings to my mind is what is the process at the commercial micro breweries? Do they raise temp at the end of active ferment? Do they hold the beer in fermentation several weeks or just dump the yeast, maybe filter and conditon and carbonate? My understanding is (not a fact,just my understanding) that the ferment is finished in a week or so, cold crashed and sent to bright tanks, without yeast or at least with the vast majority away from the beer, for carbing in a few days at most?????

Commercial brewing is usually a bit different. With the volumes and pressure one top of the yeast in those large conicals, it's best for them to dump the yeast shortly after fermentation because, unlike in the home brewer's fermenter, autolysis may actually be an issue with all that heat an pressure on the yeast. The breweries/brewbubs I've been able to poke around in seem to then transfer to a bright tank or even into the large serving vats for some extra conditioning before carbing and serving the beer. Some breweries filter, some let gravity clear the beer.
Again, that's very different from what happens in our fermenters (lucky home brewers using conicals aside). There's not enough yeast and/or pressure to cause the yeast to start dying in the timeframes we work in. So 3, 4, or even 6-8 weeks on the yeast isn't a concern for us.