A Discussion on FG & Attenuation

[Evan!]

I thought maybe we could talk about final gravity, guys. I've been perplexed by how much my average FG/attenuation ebbs and flows from time to time, while my brewing techniques have stayed approximately the same. I'll go from good attenuation and finish in the low teens to not being able to break below 1.020 for several batches in a row. Fortunately, this hasn't been a problem since the batches turn out great---it's more of a curiosity thing for me. How consistent are the rest of yous with attenuation and FG? A long time ago, about a year ago, I thought I had it figured out: just aerate the hell out of it! But alas...

I'll give you an example: Normally, US-05 has attenuation in the 70's, but when I brewed my SMaSH ale, it finished at 1.019, or 62% ADF. I was obviously concerned about bottle bombs, but it's carbonated perfectly, and it tastes like magic juice. Same thing with a lot of my brews lately, and I'm beginning to suspect the colder temps. Maybe. I like to ferment most of my ales between 65º & 70º, and with my basement being as cold as it is this time of year, they're typically to the low side. However, I've also been raising the temps to 70º or 72º towards the end of fermentation, just to help finish it out.

I oxygenate my wort with pure oxygen, so I've ruled that out. It seems to be independent of mash temps (the smoked porter I made this past weekend pooped out at 1.022, or 63% ADF, and it was mashed around 151º, whereas the HobGoblin clone was mashed at 155º, and it had 72% ADF). I can't really complain, since the beers are turning out great and I'd much rather have a low attenuated beer that tastes good than a high-attenuated beer that was fermenting in the 70's and tastes like junk. Like I said, it seems like I have these gradual ebbs & flows, and I can't seem to pin it on any one thing except maybe temps...so how about you? What are your thoughts on attenuation? How consistent are your beers WRT attenuation?

 

[BierMuncher]

My guess is that your 100% munich grain bill played havoc with your attenuation.

Mine tend to be pretty consistent (within 2-3 points), but the variance does seem tied to the amount of specialty grains that I have in the bill.

 

[Beerthoven]

Thanks for bringing this up. I've experienced the same variablity you describe. Some batches attenuate in the 70%+ range and some barely make 62%. Doesn't seem to matter if its extract or all grain, dry or liquid yeast, or pure O2 or just shaking.

My batch of EdWort's Haus Pale Ale wasn't very good and I think its because [thread=39613]it only reached 62% attenuation[/thread]. The last 12 bottles were really starting to foam up, too, but no bottle bombs. I'd like to figure this out so it doesn't happen again.

I don't have enough brews under my belt to identify a pattern yet. I aerate every batch with O2, work to get good mash & fermentation temps, and take care to pitch proper amounts of healthy yeast. Other than that I don't know what else to do.

I think its also important to understand the ingredients and how mash temp and other factors influences attenuation so that your expectations are realistic.

I'll follow this thread and hopefully learn something.

 

[Evan!]

My guess is that your 100% munich grain bill played havoc with your attenuation.

Mine tend to be pretty consistent (within 2-3 points), but the variance does seem tied to the amount of specialty grains that I have in the bill.

Does Munich have a lower fermentable proportion than 2-row or MO? That might explain the Smoked Porter too, which had Munich as its base. Maybe we're onto something here...for instance, my SBJ Pale Ale recently finished at 1.019, or 62% ADF---and it had 24% Victory and 4% Crystal. Hm, could it be?

 

[Soulive]

Does Munich have a lower fermentable proportion than 2-row or MO? That might explain the Smoked Porter too, which had Munich as its base. Maybe we're onto something here...for instance, my SBJ Pale Ale recently finished at 1.019, or 62% ADF---and it had 24% Victory and 4% Crystal. Hm, could it be?

I've experienced issues with using high amounts of Munich too. From what I gather, it has enough diastatic power to convert itself, but has less than say 2-row. So if you're using lots of 2-row, your diastatic power will be exponentially higher than lots of Munich, thus better conversion...

 

[Evan!]

I've experienced issues with using high amounts of Munich too. From what I gather, it has enough diastatic power to convert itself, but has less than say 2-row. So if you're using lots of 2-row, your diastatic power will be exponentially higher than lots of Munich, thus better conversion...

But wouldn't that translate to a lower efficiency rather than lower attenuation? I had 83% efficiency on the SMaSH ale.

 

[Soulive]

But wouldn't that translate to a lower efficiency rather than lower attenuation? I had 83% efficiency on the SMaSH ale.

Well lower conversion = lower fermentables = lower attenuation...no? If you have unconverted starches floating around, they're just going to end up as body in the final product since they won't ferment out. Anything with more body means not as attenuated...

 

[Brewing Clamper]

It's interesting that you bring this up, I have the opposite issue. Most of my beers attenuate to over 80%. My average FG is around 1.004 for the lighter stuff like pale ales, blondes and even a hob goblin clone. I've also had an oatmeal stout finish at 1.008. The only thing I can think of at the time is my choice in yeast and my mash temp but I only do a partial mash so maybe it's just the yeast. For the most part I use WLP001. This seems to be my favorite yeast, very clean. I have two brews that I'll be doing next week, I was thinking on trying to mash the grains a bit warmer this time and experiment a little. I might even split a batch and use two different yeasts.

 

[Evan!]

Well lower conversion = lower fermentables = lower attenuation...no? If you have unconverted starches floating around, they're just going to end up as body in the final product since they won't ferment out. Anything with more body means not as attenuated...

Maybe I'm misunderstanding the science here, but it was my understanding that only sugars affected gravity. When you mash higher, the starches still convert to sugars, but the higher temps means not as many chains get broken down to lengths short enough to be consumed by beer yeast. They're sugars, but they're too complex.

Is this wrong?

Then again, even if I am wrong and unconverted starches do affect gravity, I can't see this as the issue, as I never mash out until an iodine test comes up negative.

 

[Soulive]

Maybe I'm misunderstanding the science here, but it was my understanding that only sugars affected gravity. When you mash higher, the starches still convert to sugars, but the higher temps means not as many chains get broken down to lengths short enough to be consumed by beer yeast. They're sugars, but they're too complex.

Is this wrong?

Then again, even if I am wrong and unconverted starches do affect gravity, I can't see this as the issue, as I never mash out until an iodine test comes up negative.

I shouldn't have called them starches. My main point was the part about less conversion means less fermentables which means less attuative potential. Now when I use Munich in bulk, I change its potential SG in my software to compensate...

 

[c.n.budz]

I had a problem earlier this fall/winter with not hitting my target FG. I'm pretty sure I narrowed it down to temperature. The three batches that finished too high all fermented a little too cold, low 60's and probably dipping under 60 during the night. My last two batches have been kept in a small room with a space heater and the temps have held steady around 68-70. The first of those two batches finished at 1.015, close enough to my target for my tastes. The second of those batches is still in primary but I'm going to test it tonight. I've been hoping that it's just a matter of temp, but some other points mentioned here have me curious...

 

[Sea]

I also have the opposite problem. Most of my beers finish well below 1.010, and my average att.is well over 80%. Guess it's time to re-test that Traceable Thermometer!

 

[ohiobrewtus]

Maybe I'm misunderstanding the science here, but it was my understanding that only sugars affected gravity. When you mash higher, the starches still convert to sugars, but the higher temps means not as many chains get broken down to lengths short enough to be consumed by beer yeast. They're sugars, but they're too complex.

Is this wrong?

Then again, even if I am wrong and unconverted starches do affect gravity, I can't see this as the issue, as I never mash out until an iodine test comes up negative.

This is my understanding as well, but that doesn't necessarily mean that we're right.

Obviously another determining factor is going to be the yeast that you use. Nottingham will take my APA from 1.055-1.058 to 1.008-1.010 everytime. WLP051 will take that same recipe to 1.012-1.016.

On the recipes that I repeat, my results are always within 1 or 2 points of each other provided that I achieve a relatively common mash efficiency and use the same yeast in the same form. Do you always use a starter or do you occasionally pitch on an existing cake?

 

[Evan!]

This is my understanding as well, but that doesn't necessarily mean that we're right.

Obviously another determining factor is going to be the yeast that you use. Nottingham will take my APA from 1.055-1.058 to 1.008-1.010 everytime. WLP051 will take that same recipe to 1.012-1.016.

On the recipes that I repeat, my results are always within 1 or 2 points of each other provided that I achieve a relatively common mash efficiency and use the same yeast in the same form. Do you always use a starter or do you occasionally pitch on an existing cake?

This also seems to be relatively independent of the yeast, too. I've been using a lot of dried yeast lately, simply because I haven't had many batches (since the tripel twins) that required specialty strains. When I do use liquid, I always make a huge starter. In fact, the tripel twins both had excellent attenuation.

I'm beginning to think it's the temps---but the odd thing is, I don't get gushers even when I bottle-condition at higher temps.

 

[Soulive]

I'm beginning to think it's the temps---but the odd thing is, I don't get gushers even when I bottle-condition at higher temps.

Why would you? If the yeast is done with the beer in the fermenter, it won't take it any fa/urther in the bottle. Once the priming sugar is metabolized its back to sleep...

 

[ohiobrewtus]

I don't know what temperature a basement in VA typically holds during the winter but right now everything that I have in mine is holding steady at 64-65 right now and typically peaks at 67-68 in the summer. I have not noticed much fluctuation doe to temperature, but a difference of 4 degrees or so should not be expcted to have that great of an impact.

As for bottle bombs, the only one that I ever had do that to me was CCA. If I remember correctly it started at 1.060 or so and finished out at 1.014 (67%). I had 3 bottles pop about a week after it was bottled but all the others were fine. I still have 18 or so of these left and 8 months later I have yet to have another one pop, so I chalked them up to improperly mixed priming sugar or possibly too much residual yeast in the last few bottles.

Very poor attenuation should have resulted in an abundance of residual sugars across the entire batch and I should have had many more than 3 bombs. 67% is not great for the 1007 that I used, but it's not too far below the 73-77% that wyeast states for the strain.

 

[Evan!]

Why would you? If the yeast is done with the beer in the fermenter, it won't take it any fa/urther in the bottle. Once the priming sugar is metabolized its back to sleep...

Not necessarily true. I've had batches stall in the 20's, bottled them, and ended up with gushers. The yeast just stalled, but I guess when the dextrose was introduced and the yeast roused from the racking, they got back to work and not only fermented the dextrose, but some of the remaining fermentable sugars as well.

 

[Soulive]

Not necessarily true. I've had batches stall in the 20's, bottled them, and ended up with gushers. The yeast just stalled, but I guess when the dextrose was introduced and the yeast roused from the racking, they got back to work and not only fermented the dextrose, but some of the remaining fermentable sugars as well.

I was assuming you weren't referencing stalled ferments...

 

[Evan!]

I was assuming you weren't referencing stalled ferments...

Well what I'm saying is, it's difficult if not impossible to tell the difference between a stalled fermentation and one that's just finished high. My last DIPA stopped at 1.039, and I did everything I could to get it started again, but it never did. It bottled and carb'd fine---turns out the culprit was the laaglander DME. I do believe that was the last partial mash I did, aside from the Mephistopheles.

 

[Soulive]

Well what I'm saying is, it's difficult if not impossible to tell the difference between a stalled fermentation and one that's just finished high. My last DIPA stopped at 1.039, and I did everything I could to get it started again, but it never did. It bottled and carb'd fine---turns out the culprit was the laaglander DME. I do believe that was the last partial mash I did, aside from the Mephistopheles.

Yeah its tough with extracts. The highest FG I've ever had was +3 points on an all-extract batch. It was over-carbed but nothing dangerous...

 

[clayof2day]

Has everyone calibrated their thermometers recently? It could be that you are mashing at drastically different temperatures than you think you are. Pretty unlikely, but I figured I throw that out there.

 

[Evan!]

Has everyone calibrated their thermometers recently? It could be that you are mashing at drastically different temperatures than you think you are. Pretty unlikely, but I figured I throw that out there.

I calbrated my floating thermometer with my NIST Traceable one and it's accurate. Then my traceable one got ruint. My new one arrived today. But yeah, temps are good.

 

[Beerthoven]

Something I've wondered about, and this may be nothing, but how accurate are the expected yield figures found in most software (like BeerSmith, which I use), and how variable are they from year to year and lot to lot? I know maltsters are pretty good at producing consistent products, but there must be some variablilty, right?

Not all special malts are created equally either. Munich from one maltster may attenuate to a different level than Munich from another maltster, for example.

I'm just saying the target FG we are shooting for is probably much more uncertain than we think it is. BeerSmith I should get an FG of 1.012...well...how accurate is that really?

I need to start obtaining the dry-basis numbers for malts just like I get the AA figures for hops.

 

[Soulive]

Something I've wondered about, and this may be nothing, but how accurate are the expected yield figures found in most software (like BeerSmith, which I use), and how variable are they from year to year and lot to lot? I know maltsters are pretty good at producing consistent products, but there must be some variablilty, right?

Not all special malts are created equally either. Munich from one maltster may attenuate to a different level than Munich from another maltster, for example.

I'm just saying the target FG we are shooting for is probably much more uncertain than we think it is. BeerSmith I should get an FG of 1.012...well...how accurate is that really?

I need to start obtaining the dry-basis numbers for malts just like I get the AA figures for hops.

I definitely think there are nuances from product to product. That's why I don't stress over my FGs being off a couple points. Although I have to say, Beersmith has been accurate for me since I dialed it in more...