Yeast in solution vs. Yeast that has fallen out

[meadowstream]

This question is probably general, but is restricted to ale (as opposed to lager) yeast.

When we all brew, over time much of the yeast falls out of solution: there is a period of intense yeast activity and then full attenuation is reached and a huge amount of yeast then drop to the bottom of the fermenter while some yeast still remain suspended in the beer.

At this point, the beer is still very green. It tastes green and while yeast have produced the ethanol, they are still producing and reducing flavors to help achieve a far tastier beer.

Here is the question: Do the yeast in solution provide most or all of the ongoing activity or do the yeast mixed with the trub at the bottom of the fermenter also contribute mightily to good aging?

Would removing the yeast at the bottom of a conical after full attenuation positively or negatively or neutrally affect flavor?

 

[dinertime]

The yeast have to be in contact with the beer in order to take up the flavor compounds and modify them. Therefore, it is mostly the yeast that are freely floating in suspension that are doing all of the aging. Presumably the top layer of yeast in the cake could also be doing some as well.

My understanding is that during active fermentation, there is a continuous exchange between the cake and suspension, meaning that some yeast fall down to the cake while others ride up into the beer. I am not so sure that this happens after primary fermentation is complete. Does anyone else know?

As for removing the cake, that is essentially what racking the a secondary would do. I have never run a side-by-side experiment, but I don't think that it would affect the flavor much.

 

[meadowstream]

Thanks for your post. Regarding dumping trub/yeast being akin to racking to a secondary, I think that is right - and the thinking has definitely changed regarding desirability of 2ndary fermentation versus longer primary. 10 years ago, racking to secondary fermenter was universally thought of as desirable. 5 years ago that started to change until now secondary fermentation, while not rare, is no longer what most homebrewers do.

I guess my question is related to whether 2ndary fermentation will produce tastier beer. But really it is coming at it from the direction of whether yeast that is no longer in suspension is important to organic reduction. Is anything lost if you dump a large amount of yeast after full attenuation? Is that cake important as a sink for organic compounds that take away from flavor?

I am losing too much beer to the bottom of my Sankey fermenter - can I make beer just as tasty if I use a conical and dump trub and yeast a day prior to bottling/kegging?

 

[dinertime]

As I alluded to, I think the only way to really tell would be to run a side-by-side experiment. For simplicity's sake, I would probably ferment everything in primary then rack half the beer to a secondary and condition under the same environment. This way you limit the differences to only after attenuation.

As for the cake acting as a sink for compounds, I don't think so. My guess (wild speculation at this point) is that, since all of the changes to the flavor compounds are done enzymatically anyway, for the most part the same thing will happen whether the cake is there or not. It would just take longer if you remove the majority of the yeast.

Philosophically, why has the thinking changed with regards to the necessity of a secondary? I do it every time, but it's mostly for clarity purposes and/or to free up my big carboy for another primary. I know that the general consensus (at least on HBT) has moved away from secondary, so there must be a reason. It is just simplicity's sake or is it improved taste? If the former, that would suggest there is no difference in the taste. If the latter, well, obviously the yeast cake is doing something beneficial. By that line of reasoning, either way you would be better off moving to the conical.

 

[meadowstream]

All the changes to compounds are not done enzymatically - yeast are actively involved in processes that absorb some compounds and produce others. I think this is why there has been the sea change in thinking about secondary fermentation. There is a real concern that taking your beer off the yeast cake too early prevents yeast "cleaning up" your beer - and sometimes preventing that cleaning up is a reason in favor of secondary fermentation right after full attenuation.

 

[dinertime]

Even if you rack off the cake at the end of attenuation, there is still some yeast in suspension (potentially a lot depending on the flocculation properties of the yeast strain). It was my original supposition that it was these yeast cells that were doing all of the cleaning up anyway, regardless of whether there was any cake at the bottom of the fermenter.

When I said enzymatically I meant by enzymes inside the yeast. All I was getting at was that, since enzymes are catalysts, all of the 'cleaning up' could be done by a fewer amount of cells in the secondary, it just might take longer.

 

[kanzimonson]

I like to distinguish between two phases of aging - the first is after attenuation has been reached when the yeast actually do some cleanup. The second phase is not yeast dependent in my mind... it has more to do with flavors melding, micro-oxidation creating more complex flavors, and stuff dropping out.

So my theory has been to make sure that the yeast are done, and then I package the beer. If the yeast haven't cleaned up the diacetyl or acetaldehyde, then I won't remove them.

I also think that the yeast that have settled to the bottom are definitely still partially active. After all, people talk all the time about racking off the yeast cake too early and ending up with diacetyl. But wouldn't you think that the yeast in suspension are all you need to clean it up?

 

[meadowstream]

kanzimonson, thanks for your note. I don't know how to gauge the time when the yeast are done cleaning up the beer (organic work at least is done and inorganic reactions only are adding positives to the beer) or if it is measurable. Can yeast is suspension clean up the mess that 100X-10,000X yeast made? No idea!

It would be great to have a cheap, easy-to-use chromatography system to run samples through to analyze peaks and compare to style/expectations/history.

I expect that 4-5 weeks in a primary would do before dumping trub/yeast via a conical bottom valve or racking to a 2ndary or bright tank. Would be nice to have more than a rule of thumb though!

 

[dinertime]

Would you even know what to look for with chromatography? Besides VDKs (i.e., diacetyl), is there really anything that is consistently mentioned as a specific compound that needs to be cleaned up?

Not trying to sound like a jerk, I am genuinely curious. I myself have thought about how having a GC would improve my quality control.

 

[meadowstream]

I would take a Waters Empower2 or Agilent 1200 (LC not GC) and feed the peaks into a MS and identify the peaks. It would be really interesting to understand which peaks are known and anticipated compounds generally and which are novel to the style or the particular beer.

If we could get a profile of a great beer then can we run samples through to readily compare batches?

 

[dinertime]

LCMS, now we're talking heavy duty! Of course even if I still worked in a lab that had one, I wouldn't run beer samples through it for fear of the wrath of agitated grad students.

I do imagine this is what the really big commercial breweries do for quality control, but the compound profile is bound to be different for every beer, so you would have to really nail it once to use as your comparison.

 

[ChiechiBrouw]

By no means a controlled experiment, but I normally brew on Sunday, and rack to a secondary the following Sunday. Last time, however, I was busy and had to leave my beer in the primary for an extra week. This is a recipe that brew fairly frequently, so I know what it should taste like at each step.

After one week in the primary it tastes good, but unbalanced, and then after another week or four in the secondary (dry hopping) it tastes like a well-balanced, mature beer. This last time, after two weeks in the primary, it tasted noticeably more balanced and "done" when I racked it. However, after dry hopping for two weeks, I couldn't tell any difference between the one and two week batches.

When I brew a particular porter on 1098 British Ale yeast, I find that that after a week in the primary, it smells like farts and tastes like smoked beach wood (in a bad way). The smell and flavor dissipate faster if I let it sit on the yeast cake another week than if I rack it to the secondary right away. In either case, the beer tastes fantastic after two-three weeks in the secondary.

So, from my totally unscientific experiments, I tend to find that leaving it on the yeast cake for an extra week gives me the equivalent of maybe 1.5-2 weeks of aging in the secondary, but in the end I don't notice any differences.

 

[unionrdr]

Which proves that leaving it in primary longer is just as good/same in the end as the extra work of secondary after the brew is fully attenuated. But,when doing a secondary,as seems to have been mentioned,you'd have to rack it after the initial fermentation. That way,you'd still have enough yeast in suspension to do the same job as a longer primary.
So just leave it in primary. It knows what to do with no help from you or me. Just needs time,which comes with experience. You can't cheat father time at his own game.