Do Yeast Really Clean Up 'off Flavours'?

[reviled]

Ive been thinking about this a bit lately, as this winter for some reason ive been having over attenuation issues, which is wierd cos last year I was having the opposite with all my beers finishing at 1030 or 1025ish, this year they are all going down below 1010!!

I brewed a stout on monday, and checked the gravity last night and it was down to 1012, there was still a small krausen tho so there was still some fermentation happening, so because I didnt want this to dry out too much, I put the fermenter outside to sort of crash cool it, and checked it this morning its down to 12*c and the 1968 just wouldnt be capable of doing anything at that temp..

So my question is, does yeast really clean up off flavours or do anything after its finished munching on sugars? Or is that a myth? Because ive kegged beers after only 3 days of fermentation before and after 2 weeks in the keg at cold temps the beer is still clean and tasting great, sometimes cleaner than other beers I have left a full 2 or 3 weeks in the fermenter???

 

[mje1980]

I'm guessing yes, but its just a guess. I find some beers taste the same all the way through, but some change quite a bit in the space of even a week. Whether its because its in the fridge in the keg, or because of the yeast i really don't know. Hops also smooth out too.

Under 1.010 isnt really an over attenuation problem IMHO. Under 1.006 or so maybe, but i aim for my milds to get under 1.010, sometimes they do, sometimes they dont hehe. Still taste damn good though. I think the mash temp plays a big part there, and yeast amount, and yeast health. Just my.02c

 

[felten]

If the yeast is still active in the conditioning phase after primary fermentation, they will absorb or convert some by-products of their metabolism like acetaldehyde, diacetyl. Other things like higher alcohols and esters they wont, but they will change over time.

At least that is my understanding of it, I'm no expert!

 

[reviled]

If the yeast is still active in the conditioning phase after primary fermentation, they will absorb or convert some by-products of their metabolism like acetaldehyde, diacetyl.

That seems fair enough, so in saying that do you think its also fair to say if there is no diacetyl or acetaldehyde present then there is no need to warm condition after fermentation has ceased?


And mje, each to their own mate, I prefer my beers with a bit of body, im ok for a cream ale or pilsner to go below 1010, but an IPA I brewed is sitting at 1008 and theres bugger all malt character, it just would've been soooo much better if it was at 1010, or 1012

 

[Supra-Jim]

Calibrated your temp gauges etc recently Reviled? Could be another explaination for low FG's?

Cheers SJ

 

[reviled]

Im just using a crappy glass thermometer at the mo SJ, and its a different one to the one I was using last year..

Last year it was def my therm, I was mashing to hot and getting overattenuation...

This year everything has been fine until it started getting colder outside (im mashing and brewing outside), so im guessing my mash temp is dropping a few degrees in the first 15-20 mins causing my over attenuation, and without firing up the burner and stirring the mash constantly I dont see any other way around this, maybe I might start mashing a bit higher to start with?

 

[big78sam]

So my question is, does yeast really clean up off flavours or do anything after its finished munching on sugars? Or is that a myth?

I'm no expert so can only comment from my limited experience of about 10 AGs but yeast DEFINITELY cleans up off flavours for me. I ditched my first 2 AGs thinking I had an infection problem from some off flavours. Grain and grape even tasted one of my beers and thought it was probably a mild infection. Despite crazy sanitization my third had the same off flavours but I decided to persist and left it on the yeast cake for 3 weeks. By the end of the 3 weeks the off flavours we're gone. I've found I tended to get similar off flavours in the lighter styles I brew (no issues with stouts). I've stopped tasting hydrometre samples in the first week lately so not sure if it's still an issue.

I'm not sure what caused the flavours, new equipment, the yeast itself - Wyeast 1272 or something different but the yeast definitely cleaned up off flavours. IMHO if there are no off flavours from hydrometre samples immediately after fermentation has finished (or you get to your desired FG) then there's nothing to clean up so the question becomes a moot point...

EDIT: 3 weeks on the yeast cake was probably overkill, my beers are clean after 2 weeks at which point I bottle.

 

[reviled]

Cheers bigsam, what im interested to know tho, is would those flavours have cleaned up in cold conditioning as well?

My money says they probably would have, but thats a guess as I too am no scientist...

Ive had hydro samples taste awesome and the beer turns out average, and ive had hydro samples taste nasty and out of balance only to have them taste awesome in the keg after a couple of weeks in the cold.. Yet I cant stop tasting them :icon_drunk: lol

 

[reviled]

As posted by Fairlane on the realbeer.co.nz website - I found this rather interesting so thought id share


This may not answer your question, but hey... I've got time on my hands...
Now this may come across a bit textbook like but I'm basically paraphrasing a research assignment I did on yeast autolysis a couple of years ago...


Autolysis is where the yeast cell's protoplasm begins to break down under attack from it's own enzymes when the conditions are such that it can no longer grow or multiply. The yeast will then start to metabolize it's own storage reserves such as glycogens or fats, and when these are used up the cell begins to die.

Chemically, the following tends to occur
- the internal organelles of the yeast get disorganised allowing the liberation of hdrolytic enzymes
- inactivation of chemicals which inhibit these enzymes
- enzymatic degradation of intracellular molecules
- an increase in the yeast cell porosity allowing release of the degraded molecules
- further degradation of these molecules outside of the cell.

The products released include
- carbohydrates
- nitrogenous substances (amino acids, peptides)
- nucleic acid components
- fatty acids (octanoic, decanoic)
- vitamins (thiamine, niacin, biotin)

The most important of these components (as far as we are concerned) is the fatty acids. They can be described as giving aromas that are yeasty, fatty, and goaty (if you know what your goat smells like...). They also react with ethanol to produce volatile esters which will affect the aroma of the beer negatively.

Amino acids can also act as precursers for the production of lactones such as Sotolon (better known as 4,5 dimethyltetrahydrofuran -2,3 dione) which gives a nutty burnt odour and / or ethoxy-5-butryolactone which gives a green walnut odour.

Some amino acids have sulphur as a component and when they break down they can form compunds such as hydrogen sulphide (cabbage) or mercaptans (burnt rubber).

Temperature is the most impoprtant condition for control of the autolytic process... in food industries where the processing temperature is over 50deg C, and with a non ethanol environment, the process may take as little as 24hrs. In the wine industry (champagne etc...) the temperature of wine storage is approximately 10degC with a 12 to 14% ethanol environment and the autolysis may not be noted for up to 6 months.

So to try to make a relevant point.... I think that if you have your beer in keg and at low temperatures, you're not going to see many adverse effects from yeast inclusion. If anything the temp will aid settling and give you a cleaner beer. And if you've racked it off the ferment yeast, then the quantity involved will be too low to do any harm anyway...

Whole fresh yeast cells may be addded to reduce diacetyl, but then you need to deal with more autolysis... It would be preferable to condition the beer for longer periods.

Acetaldehyde is actually another product of autolysis and is seen mostly in sherry. Sherry is aged with a "flor" yeast which sits on top of the wine in the barrel, and when it dies it sinks to the bottom of the barrel and releases nutirents for continued flor growth. Along with terpenes and lactone, acetaldehyde is one key component to that nutty, slightly oxidised sherry character.

dh

 

[Nick JD]

Do Yeast Really Clean Up 'off Flavours'?

Only the ones that aren't really that "off" in the first place - the ones that are not acceptable in that style.

Hefeweizen is a good example of flavour fading (I don't think it's the yeast that does this, just breakdown of flavours) in a bad way ... but if you didn't want banana and clove then maturation would be improving the overall flavour like it does with most beers by basically making it less flavourful - taking the harsh edge off the bitterness and the grassiness off the aroma etc etc. Everything breaks down eventually, yeast or no yeast.

 

[reviled]

Everything breaks down eventually, yeast or no yeast.

I know this, however what I was referring to with my question was that all the time I see people posting how they leave their beer in the fermenter for 2-3 weeks and that it cleans up after itself etc so I just wanted to try and figure out if its just a myth or if it just doesnt matter if you keg the beer before fermentation is finished

 

[Banshee]

I found that a brew i did couple of months back was sweet and finished at 1020. The next brew finished lower. The reason for the previous brew finishing so high I believe is because I mashed on flame and I slightly cooked the malt (when I emptied the tun it was a bit burnt in one spot) therefore my temp was higher 60's. The next brew I took better care and kept good mid 60's temp and got a lower FG.

 

[manticle]

Cheers bigsam, what im interested to know tho, is would those flavours have cleaned up in cold conditioning as well?

My money says they probably would have, but thats a guess as I too am no scientist...

Ive had hydro samples taste awesome and the beer turns out average, and ive had hydro samples taste nasty and out of balance only to have them taste awesome in the keg after a couple of weeks in the cold.. Yet I cant stop tasting them :icon_drunk: lol

Interesting question. I found my beers improved markedly once following the process below:

1. Racking at around 1015 - 1020 depending on the beer.
2. Leaving for a week (roughly) following FG
3. CC for a week (roughly)

I do not know for certain if the yeast is cleaning up after itself (no brooms or mops in sight) - all I know is that I've read that's what it does and I do tend to notice a positive difference by doing it.

Could be a combination of things - could just be time and maturation, could just be yeast dropping out, could be something else.

I have at various points omitted one or two of those - might not rack a beer nor CC but just leave on yeast for a week and rack to prime. In most cases the beer that goes through all 3 phases tastes better but I've never done a side by side or proper comparison.

Based on my senses and what I've read I would (and do) recommend the above process to anyone who finds their beer tastes 'homebrewy'. Brewing science may differ (although none of these are techniques I made up).