Really overshooting the FG

[FedoraDave]

This has been happening a lot lately. The last three or so batches have resulted in a surprisingly lower FG than what I've projected using the formula of OG/4.

I'm not talking getting an FG of 1.014 when I calculated 1.016, either. I'm talking a good 0.010 lower than calculated, such as the batch of FedoraDave's American Ale that I bottled yesterday.

I had my suspicions about this batch, too. I racked to a secondary last week and dry hopped on Wednesday, and the airlock kept bubbling every 20 seconds or so. Very lazy, but still going.

I used a fourth generation washed WLP001, and the fermentation was as vigorous as I've come to expect from this yeast strain. No changes in the recipe or procedures at all, and I've made this beer at least four times in the past, and usually hit my projected FG consistently. Temps were in the low-mid 60s, and I bottled on the 20th day, as has been my habit.

As I said, this particular batch isn't the first one where the FG was quite a bit lower than projected; it's just that this one was way lower, and the recipe is one I've done before.

Thoughts?

[russki]

Dave - I would check the thermometer you use to take mash temperature for accuracy. Even the best ones tend to drift after a while and need to be recalibrated. Low FG in all-grain brewing is usually indicative of low mash temps that create more simple sugars and produce a more fermentable wort.

[ScrewyBrewer]

Dave, I've undershot my FG regularly when I was using washed yeast made into a two liter starters. Since moving last December I've been using dry yeast and some liquid without making a fresh starter and I miss the lower final gravity readings I had learned to love. A high mash pH, lower mash temperatures and viable yeast cell counts pitched all combine to have an impact on attenuation and final gravity.

[FedoraDave]

Actually, I don't take mash temperature. I'm planning on getting a mash thermometer to install in my tun, though. Even so, I use a digital thermometer in my brewing, so I don't know if that can even be recalibrated.

I've learned that if my strike water is about 10 degrees above what I want my mash temp to be, I'm good to go, and that's served me well so far.

But I'm not sure that's the issue, anyway. My OG is identical (or close enough for jazz) to the projected OG, and past OGs. If there was more fermentable sugar in the wort, it would be higher, wouldn't it?

Something's going on during the fermentation process, methinks.

[russki]

Actually, I don't take mash temperature. I'm planning on getting a mash thermometer to install in my tun, though. Even so, I use a digital thermometer in my brewing, so I don't know if that can even be recalibrated.

I've learned that if my strike water is about 10 degrees above what I want my mash temp to be, I'm good to go, and that's served me well so far.

But I'm not sure that's the issue, anyway. My OG is identical (or close enough for jazz) to the projected OG, and past OGs. If there was more fermentable sugar in the wort, it would be higher, wouldn't it?

Something's going on during the fermentation process, methinks.

Mash temperatures (as long as they are within normal range) really do not affect your efficiency, so you would have the same OG whether you mashed at 148F or 158F. What the temperature affects is enzymatic activity (alpha vs beta-amylase). Lower mash temps break starches into simple sugars ( ie glucose) while higher temps only break starches into longer, more complex sugars (ie maltose) with a higher proportion of those unfermentable by brewers yeast. It's not "more sugar", it's more fermentable sugars that cause lower FG. It's simple science - yeast can only ferment less complex sugars, but it will ferment all of them regardless of how much yeast you pitch or how warm you ferment. I would highly recommend purchasing an accurate NIST-traceable certified thermometer for brewing. Thermapen has some inexpensive models ($20 or so) that are very accurate.

[FedoraDave]

Good advice, Russki, I should act on that. It occurs to me that I have a $25 Amazon gift card, and maybe I can look into getting one there.

I've long been aware of higher mash temps being responsible for maltier beers with more body, as opposed to thinner, drier beer resulting from lower mash temps.

Good info, for sure.

[mashani]

One thing to also keep in mind when using washed yeast, especially multi generational - yeast does evolve - it adapts to brewing conditions it is exposed to. That is why there are dozens of breweries in Belgium that use "Westmalle" yeast but there beers all have somewhat different profiles and attenuation levels from their particular version of it. Each of their strains has adapted to their breweries and recipes conditions. They no longer are identical even though they are all "Westmalle" yeast.

So if you follow the same process - lets say your mash temps are a bit higher then some folks would mash at to create a highly fermentable wort - and left large sugar chains that the yeast used to not eat - over time the cells that mutated slightly and were able to eat some of those sugars will start to have an evolutionary advantage - and every generation you may end up with more of them.

Yeast is a simple animal and mutations can happen quickly, because they grow exponentially up to the point where they ferment your beer and we are talking about a huge number of reproductions and a huge number of cells. Most of the mutations are useless and make unviable cells, or cells that may cause unwanted affects (phenols/esters that were not here before and that you do not want, etc.) but sometimes one of them gets lucky. And that one lucky one will grow exponentially in that batch (or your starter and then the batch), and then in the next, and the next and ultimately if left to it's conclusion out compete anything else in the right circumstances. IE if this is what happened to you, and you keep it up, you might ultimately make the next saison yeast that attenuates 97+% if you let it evolve long enough and things don't go bad on you, IE the yeast start to make baby diaper smelling beer or something LOL.

[FedoraDave]

Fascinating dissertation, Mashani. And I see some excellent points in it. This did attenuate like a saison yeast, going all the way down to around 1.006 or so, which really raised my eyebrows.

I might actually use this yeast this summer, when the temps in my basement are higher than what I might want in a regular ale, to see what kind of results I get.