Dry yeast viability after expiration date

[worlddivides]

It's a pretty common subject that dry yeast is still really viable even after the printed expiration date on yeast, which is often 3 years after the production date. And I have experienced this myself. But I just kegged a beer that I fermented with yeast that was 5-6 months after its expiration date, and I only got 66% apparent attenuation. Granted, it was with S-04, which is possibly the yeast strain I've gotten the biggest range in attenuation from with my lowest with it being maybe 62% attenuation and my highest with it being 85% attenuation. But that 62% was in a beer that I had mashed really high. This beer was mashed at 149F / 65C. And for reference, the beer immediately before it had 85% attenuation and the beer immediately before that had 78% attenuation, and both of those were mashed slightly higher (152F and 151F), so I do think it might be due to the expiration date. That said, I tasted the beer before kegging it and it tasted pretty damn good, so there was no reason to throw it away. It's also possible that before I purchased the yeast, it hadn't been stored in a refrigerated environment that entire time, which might have lowered the viability more. In the old days, I used to rehydrate dry yeast before pitching, but I haven't done that in years. Maybe it would be better to do that (or if it's old enough maybe even do a starter, though I've never made a starter for dry yeast) since the viability might be down. But I thought it was interesting how low the attenuation was, both compared to other yeasts and to most previous experiences with S-04.

 

[odie]

I doubt it was anything to do with the age of the yeast. Each batch is going to be a little different. Anything from mash temps, sparging, OG, fermenting temperature, fermentation time...

but barely expired yeast? no. that stuff is healthy and viable well beyond those dates.

 

[Steveruch]

that stuff is healthy and viable well beyond those dates.

I've used dry yeast over four years past the best by date with no problems.

 

[dmtaylor]

I would check calibration of your hydrometers or refractometer before anything else. These things fall out of calibration easily. Dropped on the floor recently? Check also that your mash thermometer is reading accurately, same kind of thing.

 

[Brewer dad]

I would wonder about OG and fermentation temp as well.

 

[odie]

honestly, if you expect identical results every time...home brewing is not for you. you will always be disappointed.

Brewing is an art form, not a science.

If you want "science", drink corporate beer.

 

[MaxStout]

Did your mash bill include grains with lots of unfermentables, like dextrin malts, crystal, etc.?

 

[worlddivides]

honestly, if you expect identical results every time...home brewing is not for you. you will always be disappointed.

Brewing is an art form, not a science.

If you want "science", drink corporate beer.

Whoever said I expected "identical results"? Brewing is just as much "science" as anything else. I was simply saying that the 66% attenuation was quite a bit lower than I expected, especially given the low mash temperature (though, as I mentioned, not the first time I've had S-04 with low attenuation. I've had S-04 as low as 62% attenuation and for other English yeasts, I've had attenuations as low as 55% with Windsor. But I typically expect S-04 to be in the 70-80% range). I had assumed that the expired yeast could be a factor, but on second thought, it probably wasn't, given the lower gravity, lower volume of wort, and other factors.

The OG was 1.042 and the FG was 1.014. I did not expect the 1.009 that Brewer's Friend estimated since it tends to just blindly guess without taking all the factors into consideration. Fermentation started at 66F and ended at 69F. The lowest the fermentation temperature went was 65.5F and the highest it went was 69.4F.

The hydrometer falling out of calibration is certainly a possibility, but I don't think that's it.

I think MaxStout might be right. While everything in the mash bill was fermentable, it did include some specialty grains (such as flaked barley and roasted barley) that have low fermentability and that can't convert without the enzymes in the base malt. It's possible those might have been enough to raise my expected FG from around 1.010 - 1.012 to 1.014. It does make me wonder, though, how I've gotten stouts with a much higher percentage of those kinds of grains (flaked, crystal, roasted, chocolate, patent, etc.) to get down to 1.008 before. Granted, those were often with a yeast like Nottingham or US-05. And the 85% attenuation I once got with S-04 was with an ale that only had a small amount of flaked wheat and light crystal other than the base malt.

 

[Whisky River]

It might have been a combination of little things like you mentioned above. I was also pretty surprised that the lowest temperature recommendation for US-04 and US-05 is only 64.4f. I had a batch going with US-05 recently that was pretty sluggish fermenting at 65 but did a bit better a few degrees higher. Maybe your low temperature of 65.5 slowed them down a bit, possibly even a lot if your fermentation thermometer was off a degree or two.

 

[worlddivides]

It might have been a combination of little things like you mentioned above. I was also pretty surprised that the lowest temperature recommendation for US-04 and US-05 is only 64.4f. I had a batch going with US-05 recently that was pretty sluggish fermenting at 65 but did a bit better a few degrees higher. Maybe your low temperature of 65.5 slowed them down a bit, possibly even a lot if your fermentation thermometer was off a degree or two.

It's a temperature probe in a thermowell hooked up to a controller, and it's a pretty accurate one too. My last beer that I fermented with S-04 was actually fermented several degrees lower and it was just as aggressive of a fermentation and ended within 3 days. I typically brew US-05 at between 66F and 70F, while I brew S-04 at between 63F and 68F.

Your post did make me wonder, though, so I just went through and looked at all the beers I've brewed with both S-04 and US-05 over the past year and, although this one at 66% attenuation was the lowest, my last three with S-04 before that were 70%, 72%, and 69%. On the other hand, in comparison, my last four with US-05 were 78%, 80%, 75%, and 81% attenuation. All of the US-05 brews fit within the normal range, but the S-04 ones are on the low end. I do think that it's possible that specialty malts like crystal, brown, amber, roasted, flaked, and so on may be the main reason overall for that since I tend to use S-04 for beers that tend to be much higher in specialty malts (since I primarily use it for English-style beers, especially stouts, porters, brown ales, and so on). And the 85% attenuation I got with it once was with 100% Maris Otter.

 

[dmtaylor]

I just went through and looked at all the beers I've brewed with both S-04 and US-05 over the past year and, although this one at 66% attenuation was the lowest, my last three with S-04 before that were 70%, 72%, and 69%. On the other hand, in comparison, my last four with US-05 were 78%, 80%, 75%, and 81% attenuation.

These numbers all look to be on the low end. For S-04, my beers are seeing 77, 78, 78, 80, 82% attenuation. And these beers all have varying amounts of adjuncts which would tend to reduce attenuation slightly... but at average 78%, I am not really seeing it. And for US-05, I am seeing 84, 86, 85, 76, 81% attenuation on my last 5 batches, with average 83%. If ALL your beers are attenuating fairly low, again I recommend checking calibration of your mash thermometer and your hydrometer and/or refractometer as applicable because something ain't right, and I calibrate all of mine like a hawk, always have and always will.

EDIT: By the way... that 76% that I had on US-05... was for a sweet stout where I used a lot of unfermentable lactose. Makes a lot of sense. So my true average for this yeast is closer to 84%. Again, varying amounts of adjuncts but pretty darn consistent attenuation anyway, much higher than you are seeing.

 

[worlddivides]

For US-05, the 75% is the only one that's outside of their listed range (which Fermentis has as 78% to 82%):

https://fermentis.com/en/product/safale-us‑05/

And, although that 75% attenuation beer was mashed at 151F, it was 7% Crystal 60L, 5% flaked wheat, and 5% Carapils, which might help explain the slight drop.

But the other 3 numbers I gave for US-05 : 78%, 80%, and 81% are not on the low end at all.

My S-04 numbers are definitely on the low side, but I doubt it's due to a mash thermometer (since my US-05 numbers are not low -- and my most recent beer before this one, which was neither US-05 nor S-04, had 85% attenuation, and I've recently had beers with FGs of 1.007 and 1.004) and also because I still have records from 11 years ago when I first started with extract and S-04 also was in the mid 60s to low 70s in attenuation then as well (I do have records of S-04 in the uppers 70s from back then, but not at the very beginning, and even then I still had an occasional 69% mixed in with 75%, 78%, and 80%s). And that's all with a different hydrometer and no mash at all.

If my low numbers with S-04 are abnormally low (since, unlike US-05 which are within the normal listed range, my S-04 numbers are below their listed range) and it's not the specialty malts, then I have to wonder what the factor is that makes S-04 different for me.

 

[dmtaylor]

I guess I forgot to mention... Fermentis' posted ranges are not accurate.