Low FG with US-05

[slurms]

So, I've had an American brown ale in primary for about 10 days so far (recipe below). Decided to check its gravity reading (actually, an adjusted refractometer reading) and it seems pretty high. Started with an OG of 1.056 and am reading at 1.017 w/ 5.3%abv (refrac. reading of 8.2B converted to those numbers). That's an apparent attenuation of ~70% using US-05. Every other time I've gotten 80-85% attenuation...

My only guess at the moment is that the mash was warmer than when I normally use US-05 (156F compared to 150-152F). Could that really make me drop 10+% attenuation? Seems kinda dramatic...

Given that it's been 10 days, I imagine it's done fermenting (though plan to leave it in primary for a 3 weeks total); it's pretty clear with most stuff settled. I suppose there's an off chance that it's still working its magic (sight unseen) but I don't believe that. Anyone have a similar experience like this? I'm okay with something like this being slightly on the sweeter side, but 1.017 is just a bit too much, especially without the extra ABV (was expecting somewhere around 6-6.25%)

3 Gallon batch
60 min mash
156F mash (strike was a bit too warm but settled to 156 with grain and some stirring)
60 min boil
OG: 1.056

Grain Bill
2 Row - 4.25lb (68%)
Munich - 1.5lb (24%)
Crystal80 - 0.25lb (4%)
Chocolate - 0.25lb (4%)

Hops
Cascade - 0.4 oz @ 45min (20IBU)
Willamette - 0.3 oz @ 15min (5IBU)

Cooled to ~70F in ~15mins
Pitched 1 packet of US-05
Fermented in room temperature ~62-65F

 

[Rob2010SS]

That shouldn't make it finish that much higher. Do you know what the highest temp was after dough in and how long it took you to get to 156F?

The only reason I ask is a lot of times, the mash is complete much quicker than 1 hour. So if after dough in, you were at something as high as like 165F for more than 10-15 minutes, I could see that affect it.

The other thing is using a refractometer after fermentation. I don't use a refractometer but I know there's some calculations you have to do to figure out the gravity after there's alcohol present. Are you 100% sure you're right in your calculation?

 

[dmtaylor]

Have you calibrated your mash thermometer in both boiling water adjusted for your elevation above sea level (might NOT be exactly 212F), and in ice water at 32F? If you haven't, if your thermometer is off by a couple of degrees which is very likely, if you mashed at 158F or even 160F, that definitely explains it.

Also, did you measure mash pH? What was it?

EDIT: Your refractometer correction looks good to me, I don't think that's it. However, @Rob2010SS has a good point, if you mashed in too hot like 165F or more even for a few minutes, you might have killed off much of the enzymes, could be another temperature related thing.

 

[slurms]

The only reason I ask is a lot of times, the mash is complete much quicker than 1 hour. So if after dough in, you were at something as high as like 165F for more than 10-15 minutes, I could see that affect it.

I think the temperature after doughing in was 160-162F for less than 5 minutes (first time doing a 3 gallon with BIAB so definitely over shot the strike temp there...) and then settled to ~156F. I mean, maybe that was enough to bump up the unfermentables.

The other thing is using a refractometer after fermentation. I don't use a refractometer but I know there's some calculations you have to do to figure out the gravity after there's alcohol present. Are you 100% sure you're right in your calculation?

I've used these calcs for adjusting FG with brix for all of my 1 gallon batches and it seems to match up with recipe builders more or less so I'm not terribly concerned with that.

Have you calibrated your mash thermometer in both boiling water adjusted for your elevation above sea level (might NOT be exactly 212F), and in ice water at 32F?

That's possible. Though I've been using the same thermometer for all my other smaller batches and it seems to be fine in that regard.

Also, did you measure mash pH? What was it?

I didn't measure mash pH (don't have a pH meter). Though I used Bru'n water which estimated the pH around 5.5 or so (don't know exact but it was in the right ballpark according to the program).

 

[dmtaylor]

I think the temperature after doughing in was 160-162F for less than 5 minutes (first time doing a 3 gallon with BIAB so definitely over shot the strike temp there...) and then settled to ~156F. I mean, maybe that was enough to bump up the unfermentables.

Less than 5 minutes is *probably* okay. But like I said, if your mash thermometer is off by a couple degrees and you still don't know it, it could still be the main cause.

I didn't measure mash pH (don't have a pH meter). Though I used Bru'n water which estimated the pH around 5.5 or so (don't know exact but it was in the right ballpark according to the program).

Bru'n water is good, and 5.5 is good, so this is probably not a pH problem.

I'm sticking with thermometer calibration. Look up the boiling point for your area, measure boiling vs. ice water and see where your errors come out. I know with my thermometer, it's high by like 2 or 3 degrees on one end, and low by 2 or 3 degrees on the other end (I forget which end was which), and this led me to understand that at mash temperatures in the 150s, the two errors effectively cancel out so my mash temps should be accurate within about 1 degree! But everybody will not be so lucky, every thermometer is different.

 

[slurms]

Look up the boiling point for your area, measure boiling vs. ice water and see where your errors come out.

Just tried this out with the thermometer I used on that brew day. Seems to be reading 2F greater on the high side and 4F greater on the low side. So I guess my mash was more closer to 158F. Though, I still feel that shouldn't have that dramatic of an effect of the attenuation.

I tried the same thing with the short stubby thermometer I recently got to put into the weldless bulkhead/hole(whatever you wanna call it) on my mash/boil kettle. Reads fine for freezing but quite low for boiling. I think it has to do with the pot not being covered by the lid (the first thermometer fits in the steam vent/hole in the lid).

Also, I just realized I titled this "Low FG" when it should have been "High FG" because, well, I'm an idiot...

 

[day_trippr]

"Brain Cramps Happen".
I was surprised to see the thread veered opposite the title

Cheers!

 

[slurms]

if you mashed in too hot like 165F or more even for a few minutes, you might have killed off much of the enzymes, could be another temperature related thing.

Would the killing off of enzymes affect the OG (i.e., a much lower OG than anticipated?). I hit my OG within a few points (I think my mash efficiency was a bit different than I assumed, but was happy with it overall). Unless it's something like, while there were enough sugars in the wort to read the right OG, there wasn't enough enzymatic activity to convert them to useful yeast food. If that's the case, I could definitely get behind the idea of the high mash temps at the first few minutes killing things off.

 

[dmtaylor]

Would the killing off of enzymes affect the OG (i.e., a much lower OG than anticipated?). I hit my OG within a few points (I think my mash efficiency was a bit different than I assumed, but was happy with it overall). Unless it's something like, while there were enough sugars in the wort to read the right OG, there wasn't enough enzymatic activity to convert them to useful yeast food. If that's the case, I could definitely get behind the idea of the high mash temps at the first few minutes killing things off.

My guess is the alpha enzymes, which are more sturdy, survived, but you killed off most of the beta amylase right away, resulting in the high FG (low attenuation). In other words, the alpha that didn't die off will still give you the right OG and efficiency, while without beta, your FG will be high. I have seen this happen in my own brewing. It happens, it's real, and I think it's the final answer.

I'm glad your first thermometer isn't too far off. Not sure what to tell you on your new one, except not to rely on it too heavily apparently, until you fully understand how to adjust mash readings from it.

 

[slurms]

My guess is the alpha enzymes, which are more sturdy, survived, but you killed off most of the beta amylase right away, resulting in the high FG (low attenuation).

That makes perfect sense. I wasn't aware that the beta would "die off", but I guess once it's hot enough to denature the protein (if that's the right word I remember from high school chemistry) then it is done for good.

I'm glad your first thermometer isn't too far off. Not sure what to tell you on your new one, except not to rely on it too heavily apparently, until you fully understand how to adjust mash readings from it.

It was odd. The first one showed 214F for boiling only when the lid was on the pot and the probe was through the lid steam-hole. It shows ~180-190F (don't remember which) with the lid off. The new thermo read the same thing with the lid off. I would think that boiling water should read at ~212 if the lid is on or off... But that's a topic for another day I suppose.

 

[dmtaylor]

"Denatured" is indeed the proper term. I say "die" loosely just because I'm loose like that.

 

[VikeMan]

@slurms I ran your grain bill, mash length and temp (revised to 158F), and yeast strain through BrewCipher. For your OG of 1.056, BrewCipher predicts an FG of (wait for it).... 1.017.

Your grain bill is not particularly very fermentable, but the mash temp is the big driver here.

 

[slurms]

@slurms I ran your grain bill, mash length and temp (revised to 158F), and yeast strain through BrewCipher. For your OG of 1.056, BrewCipher predicts an FG of (wait for it).... 1.017.

Wow, look at me being spot on... I'll have to check out that program. I put it into BrewersFriend recipe builder and was putting me somewhere around 1.011 or so (could have missed something there though).

Your grain bill is not particularly very fermentable, but the mash temp is the big driver here.

Is Munich much less fermentable than 2-row? Or at least at that temp?

 

[VikeMan]

Is Munich much less fermentable than 2-row? Or at least at that temp?

Munich is indeed less fermentable than 2-row brewer's malt. And the C-80 is less fermentable than either of those. Then there's the chocolate...

 

[Rob2010SS]

@slurms I ran your grain bill, mash length and temp (revised to 158F), and yeast strain through BrewCipher. For your OG of 1.056, BrewCipher predicts an FG of (wait for it).... 1.017.

Your grain bill is not particularly very fermentable, but the mash temp is the big driver here.

I'll have to check out that program as well! I also ran it through Brewer's Friend and it gave me 1.013 and FG.

 

[day_trippr]

Most of the recipe builders are quite limited in their understanding of the actual brewing process
From my albeit limited understanding, BrewCipher is much smarter than most in that regard...

Cheers!