Reusing Yeast And Fusel Alcohols

[fw00r]

Hi all,
I have been reusing yeast slurry without problem for a little while now, Say 3 months.

My most recent brew has a problem with Fusel alcohols I believe. I am wondering if the yeast will produce a higher percentage of fusel alcohols as it gets re-used or if it is just a temperature issue as we are coming up to summer and the temp (due to thermostatically controlled heaters) is fluctuating more. Is this due to mutation or stressing the yeast out?
I dont think the yeast has been used more than 5 times but I might be mistaken.

Any input is welcome.
Thanks

 

[Stuster]

Fusels can be due to high temperature. It may be that the warmer weather has been the problem for you. If you are re-using the whole yeast cake that might be a problem. The very vigorous fermentation can mean the temperature in the middle of the liquid is much higher than ambient so even though you think it's fermenting at a reasonable temperature it may be too hot. So how hot was it fermented and how much yeast did you use?

Re-using the yeast cake does mean more chance of contamination, so it also may be due to some wild yeast that has produced more fusels, even if the beer was fermenting at a temperature that would have been fine with the original yeast. Are there any other strange tastes? What sort of attenuation did you get?

 

[blackbock]

Are you K+K or AG fw00r? I have heard that brews containing a high proportion of sugar/dextrose can cause runaway fermentation which might in turn elevate the temperature and cause that problem. Also, reusing slurry five times is an open invitation to infections, and definitely to mutations. If extra fusel production is the worst you've experienced then I'd say you've done well.

As far as attenuation goes, if you have produced lots of fusels, this would increase the density of the wort and show higher apparent attenuation than a cleaner wort would, wouldn't it?

Edit: That last bit is back to front: a denser liquid would show a higher hydro reading, not higher attenuation!

 

[Stuster]

BB, I was more thinking that if there was some contamination there, he might have higher attenuation than normal for his yeast, as the yeast/bacteria might chomp on more of the sugar. I'm not sure about the density of fusel alcohols. (After a quick google, it seems that fusel alcohols are lighter than water, so they'd still lower the density and thus increase the apparent attenuation.)

 

[Screwtop]

Have noticed in the past that repitched yeast sometimes resulted in fusel type smell/taste. Cut back from using 250ml now to using only 150ml when repitching (for 23L) seems to have fixed the problem. Seems to occur only with some yeasts. Not really convinced that the small increase in temp during active fermentation is the cause though. Using W 3068, repitching 250ml results in much lower production of the banana ester (iso amyl), so I now pitch lower to stress the yeast a little to overcome this.

 

[fw00r]

I brew extract and OGs haven't been very high, Maybe 1.060 at the highest.

I have been using US-56 or S-04 as yeasts and pitching a volume >150ml in a 23L brew.
Reducing the pitch volume is a possible solution as my 50L batch didnt show signs of the fusel alcs... But the 50L batch also didnt have a heater that could get it near 20deg C, It remained at around 16deg C.

As far as I know the temps havent got past 22deg c on my 23L batches. My heaters lowest setting is 20deg C.

I dont think runaway fermentation is my problem exclusively but may be an issue as the ambient temp goes up.

I think the apparent attenuation is around 70% (1.055 to 1.016) and no bottle bombs or overcarbonation. Crystal malt is used in my brews.

I am fairly confident there isnt an infection though I cant rule it out completely.

Thanks again for your time!

 

[Stuster]

I'd guess it's just the temperature then if the bigger batch was fine. I'd get rid of that heater, or at least there's no need to use it if the temperature is 16C. That's a great temperature to brew with those yeasts, especially US05 (US56's new name). US05 will ferment nice and clean at that temp with no problem at all. It'll go lower than that even. Certainly keeping it at 18C or less is great for the majority of ale yeasts (some Belgians, wheats etc are a bit different).

 

[fw00r]

I'd guess it's just the temperature then if the bigger batch was fine. I'd get rid of that heater, or at least there's no need to use it if the temperature is 16C. That's a great temperature to brew with those yeasts, especially US05 (US56's new name). US05 will ferment nice and clean at that temp with no problem at all. It'll go lower than that even. Certainly keeping it at 18C or less is great for the majority of ale yeasts (some Belgians, wheats etc are a bit different).

I find it a little odd that the temp would be the issue now especially because the heater is thermostatically controlled.
The heater has been used in all my batches since I got it some 9 months or more ago. I have a feeling that the smaller batches will not be able to maintain their temp but certainly worth a try in the quest for fewer headaches B)

 

[Plastic Man]

fw00r

Might be worthwhile doing a few batches with liquid yeast to see if that makes a difference. I remember hearing an interview with Dave Logsdon (spelling ???) from Wyeast and he rekoned the process of drying yeast introduced contaminants. He wants to sell liquid yeast of course but there's been plenty debate in the past regarding whether or not to repitch dried yeast. Might be worth a try.

 

[ohitsbrad]

I have had a similar problem in one beer. It was an extract based version of Ross's Nelson Sauvin summer ale. I reused US56 yeast and pitched probably 200ml of slurry for a 20L batch. What I noticed at bottling in the fermenter, and in some of the finished bottles, was a strange alcoholic smell possibly like kerosene. There was also a definite banana character which I put down to the yeast, but did not expect or want from US56.

I suspect like Screwtop said that at least in my case it's not due to the fermentation temperature but maybe pitching too much, not having a good method to re-use only the top white layer of yeast, and also that reusing dry yeast is maybe not ideal.

Have noticed in the past that repitched yeast sometimes resulted in fusel type smell/taste. Cut back from using 250ml now to using only 150ml when repitching (for 23L) seems to have fixed the problem. Seems to occur only with some yeasts. Not really convinced that the small increase in temp during active fermentation is the cause though. Using W 3068, repitching 250ml results in much lower production of the banana ester (iso amyl), so I now pitch lower to stress the yeast a little to overcome this.

 

[mfdes]

From my experience there are a few things to keep in mind:

Re-using dried yeasts is not very recommended as they're more prone to infection. However from what I know newer production methods have cut this out a lot, and perhaps it's possible to do so more safely. I still would not reuse a yeast more than 3-4 times.

Yeast temperature if overpitched will rise significantly above ambient as stated above. This will give you more fusels.

US-05 is cheap. Why the need to reuse so much? Use fresh yeast every 2nd or 3rd brew if you want to save.

Wyeast 1056 and WLP001, which are reputedly the same strain as US-05, are also renowned for losing vigour after several repitches without reculturing. Many microbrewers use other US strains for this reason.

MFS

 

[Sammus]

I think I remember reading somewhere that overpitching can cause this. Someone correct me if I'm wrong.

 

[blackbock]

Wyeast 1056 and WLP001, which are reputedly the same strain as US-05, are also renowned for losing vigour after several repitches without reculturing. Many microbrewers use other US strains for this reason.

I have read other brewers on this forum making the exact opposite claim about that exact strain, Trough Lolly comes to mind. He claimed that the yeast actually improves with successive repitches! So, really I'm not sure there can be a definitive answer on this one.

 

[mfdes]

To a point it improves: It's great when used a second time in a big beer after having been used first in a smaller one. However I've heard microbrewer guests in BBR and maybe also the Jamil show state that they'd prefer if this strain was stabl enough to be repitched multiple times. After five or so repitches it starts to lose it, compared to its peak performance and that of other yeasts.

Also, it is more common for underpitching to cause excessive esters and fusels.

MFS.

 

[Jye]

My experience is that repitching from the yeast cake is beneficial. The yeast is healthier and it allows you to pitch at the correct rate. But you do need good temp control as the larger amount of yeast will raise the temp more than the first pitch from a starter or satchel and this was most likely the cause of fusel alcohols.

The last couple of batches with US-05 I have been pitching directly onto the yeast cake and these beer have gone on to do well at comps. But you do need to pitch cold so the temp can be controlled.

5 times is probably a couple to many repitches unless you wash your yeast in some way, Ive had no problems go 3 generation before starting again.