Stuck Fermentation? Amber Lager

[Madru]

Hello guys!

I'd like some tips from my colleagues on understanding a possible stuck fermentation.

I prepared an all-grain recipe for an amber lager with the following characteristics:

Pre-boil gravity: 1.041 (expected 1.041)
Post-boil gravity: 1.046 (expected 1.050) Initial gravity: 1.046 (expected 1.050)
Final gravity: Stalled at 1.022 (expected 1.010).

I started fermentation (30/08) with OG at 1.046, 18L batch, 2L of starter with one each of Angel's BF16. Initial temperature of 13°C for 4 days, I took the SG reading and it was at 1.022, I raised it to 14°C for a day and then 15°C, I measured the SG again and it was still at 1.022. I left it for another 4 days at 15°C and the SG was still at 1.022 (10/09).

What could be the problem, lack of yeast? lack of sugar? Boil time?

The flavor is very good, but low ABV, should I consider it finished? Or should I try to strengthen the wort with a starter or a little sugar to increase the ABV?

Any tips I appreciate!

 

[dmtaylor]

Our first guess is that you are using a refractometer, which is not accurate when alcohol is present. Or are you using a float hydrometer? Assuming refractometer, you need to use an adjustment calculator to get the real result. Take measurements in Brix and go to Part II: https://www.brewersfriend.com/refractometer-calculator/

If that ain't it, then we'll discuss other things with you like mash temperature, that's the other biggie.

 

[Madru]

Our first guess is that you are using a refractometer, which is not accurate when alcohol is present. Or are you using a float hydrometer? Assuming refractometer, you need to use an adjustment calculator to get the real result. Take measurements in Brix and go to Part II: https://www.brewersfriend.com/refractometer-calculator/

If that ain't it, then we'll discuss other things with you like mash temperature, that's the other biggie.

Thanks for the quick reply. But I'm actually using a float hydrometer.

 

[Sandy Feet]

I don't know what that yeast does, but yes, you need a massive pitch rate for a lager. I also don't know your mash temperature. Don't open the thing up until you package. Let it ferment for a total of 14 days. If it is still high, it is high. It is what it is.

 

[dmtaylor]

Okay then, you likely mashed too hot or too short. What was your mash time and temperature?

There are other variables, but like I said, these are all the big ones.

Pitch rate and yeast cell count most likely have nothing to do with anything. We can discuss that later IF need be.

 

[Minbari]

Okay then, you likely mashed too hot or too short. What was your mash time and temperature?

There are other variables, but like I said, these are all the big ones.

Pitch rate and yeast cell count most likely have nothing to do with anything. We can discuss that later IF need be.

Agree with this. First thing I think of in stuck fermentation is mash temp.

As said, yeast will grow and consume the sugar. Even if under pitched. (Off flavors are another issue)

 

[Madru]

Hi guys,

Thanks for the tips.

My recipe and directions below.

Brew Method: BIAB
Style Name: International Amber Lager
Boil Time: 30 min
Batch Size: 18 liters (fermentor volume)
Boil Size: 25 liters
Boil Gravity: 1.040
Efficiency: 70% (brew house)

Hop Utilization Multiplier: 1

STATS:
Original Gravity: 1.050
Final Gravity: 1.010
ABV (standard): 5.16%
IBU (tinseth): 26.01
SRM (ebcmorey): 18.82
Mash pH: 0

FERMENTABLES:
2.58 kg - Pilsner Malt (61.7%)
1 kg - Vienna Malt (23.9%)
0.45 kg - Caramunich Type 2 (10.8%)
0.15 kg - CaraRed (3.6%)

HOPS:
25 g - Cascade, Type: Pellet, AA: 6, Use: Boil for 5 min, IBU: 4.62
12 g - Herkules, Type: Pellet, AA: 15, Use: Boil for 30 min, IBU: 21.39

OTHER INGREDIENTS:
1 each - Yeast Nutrient, Time: 10 min, Type: Other, Use: Boil
1 each - Whirlfloc, Time: 5 min, Type: Other, Use: Boil

YEAST:
Angel Yeast - BF 16 Lager Yeast
Starter: Yes
Form: Dry
Attenuation (avg): 80%
Flocculation: High
Optimum Temp: 8.89 - 12.78 C
Fermentation Temp: 13 C

PRIMING:
Method: co2
Amount: 0.88 bar
CO2 Level: 2.5 Volumes

MASH GUIDELINES:
1) Infusion, Start Temp: 70 C, Target Temp: 68 C, Time: 45 min, Amount: 15 L
2) Sparge, Start Temp: 78 C, Target Temp: 75 C, Time: 10 min, Amount: 10 L

 

[J A]

If you actually mashed at 68C, it's on the high side for a lager, in my opinion. That's over 154 F and while it's possible to get fermentables at that temp, I think it's pushing it. If your temp control was less than accurate and you mashed any higher than that, it's very likely a factor in under-attenuation. For single infusion in lagers, kolsch, cream ale, etc, 152F is common. I personally use a step-mash schedule that spends most of the time at 148F and raises to 158F for dextrin rest.

 

[HighVoltageMan!]

First off, I'm not convinced that mash temperatures have a huge impact on attenuation, it's the yeast that drives final gravity. That being said, you did mash too high for the style (should been closer to 64C), plus you have 11% Cara-Munich II, plus you added Cara-red for a total of nearly 15% cara-malts. The yeast will likely chew through the higher mash temps, but the Cara-Munich II/cara-red is really not the best choice for several reasons. First it will cause the FG to be higher than one would expect, second is that it makes the beer sweet and not in a good way.

I think that despite the mash temps and the cara-munich you should see a final gravity of 1.015-1.017 or so. Still high, but not 1.022. The other thing I would check the accuracy of you hydrometer. I have had some that gave me less than accurate results. If possible, double check the your reading against another hydrometer or if you have a refractometer, use that to measure the gravity. You will need to run those number through the refractometer calculator because alcohol is present. Lastly, taste the beer. It may not be perfect, but it's still drinkable and enjoyable.

Next time drop the cara malts entirely. If you want some color, add a little Munich malt and/or increase the Vienna. This beer should beer fairly dry, but still malty. Expect a FG of 1.008-1.009. Nice and dry.

Edit: If you made a starter with dry yeast, it still needs to aerated. If you made it with 2 packs of dry yeast (11 grams x 2), you could just throw it in as is, or rehydrate prior to pitching. In both cases, aeration is not required. Rehydrating the yeast shortens lag time a bit.

Your pitch rate on this beer was fine, it just needed some oxygen.

 

[J A]

First off, I'm not convinced that mash temperatures have a huge impact on attenuation, it's the yeast that drives final gravity. That being said, you did mash too high for the style (should been closer to 64C), plus you have 11% Cara-Munich II, plus you added Cara-red for a total of nearly 15% cara-malts. The yeast will likely chew through the higher mash temps, but the Cara-Munich II/cara-red is really not the best choice for several reasons. First it will cause the FG to be higher than one would expect, second is that it makes the beer sweet and not in a good way.

I think that despite the mash temps and the cara-munich you should see a final gravity of 1.015-1.017 or so. Still high, but not 1.022. The other thing I would check the accuracy of you hydrometer. I have had some that gave me less than accurate results. If possible, double check the your reading against another hydrometer or if you have a refractometer, use that to measure the gravity. You will need to run those number through the refractometer calculator because alcohol is present. Lastly, taste the beer. It may not be perfect, but it's still drinkable and enjoyable.

Next time drop the cara malts entirely. If you want some color, add a little Munich malt and/or increase the Vienna. This beer should beer fairly dry, but still malty. Expect a FG of 1.008-1.009. Nice and dry.

Edit: If you made a starter with dry yeast, it still needs to aerated. If you made it with 2 packs of dry yeast (11 grams x 2), you could just throw it in as is, or rehydrate prior to pitching. In both cases, aeration is not required. Rehydrating the yeast shortens lag time a bit.

Your pitch rate on this beer was fine, it just needed some oxygen.

Agreed with all that except that I think mash temp has to impact final gravity. If dextrins are the majority of the product of conversion, the yeast has less to convert to alcohol. That being said, I doubt that mash temp alone, in this case, is responsible for a 10-point miss in FG. Here, as you note, the Cara/Crystal malts and lack of O2 are probably big factors.

 

[HighVoltageMan!]

I think mash temp has to impact final gravity

I should been clearer. I believe it does, but the yeast has a bigger impact on final gravity.

 

[dmtaylor]

You mashed kind of hot, and kind of short. That, plus the large amount of caramel malts, is what's happened here.

Check the calibration of your hydrometer, AND check that your mash thermometer reads exactly 0 C in ice water and exactly the boiling point temperature for your elevation above sea level (probably not 100.0 C, look this up online for YOUR elevation above sea level). If you actually mashed a degree or two hotter than you thought, then all your beta amylase would have been destroyed almost immediately in the hot mash, causing higher FG.

I still think the choice of yeast and health of yeast probably has nothing to do with anything. It's possible, but less likely than what I've said above.

 

[Bigbre04]

I would agree with the above that the high mash temp/short mash is to blame here.

For next time:
i shoot for 149 on everything. mash in at 151. i recirc my mash for 1 full hour before heating the total vessel to mash out temp for my system i shoot for 176 in order to get the liquid coming out the top to read 170. Boil for 1 hour and then cool before knocking out at the correct temp. I generally shoot for the center of the recommended range as the knock temp and then set my glycol for the ferm temp based on what i want out of the final beer.

Dont do a yeast starter, it is not needed anymore. I generally overpitch all of my beers with dry yeast.

I agree with the above that reducing some of your cara malts can help. if you want additional color add a small amount of roasted malts(i use alot of chocolate and midnight wheat, but any would work in small amounts).

Time may help with further attenuation, but be careful of infections.

 

[Madru]

Thank you guys for all the excellent recommendations.
I'll check with an auxiliar hydrometer to make sure the FG is correct.
I'll definitely make this recipe again with the recommended adjustments to the mash, grains, and times. I'll test how it turned out after carbonation and share it with you.

 

[Bigbre04]

Thank you guys for all the excellent recommendations.
I'll check with an auxiliar hydrometer to make sure the FG is correct.
I'll definitely make this recipe again with the recommended adjustments to the mash, grains, and times. I'll test how it turned out after carbonation and share it with you.

be sure that your samples are at the calibration temp for your hydrometer, unless your hydrometer has a temp adjustment built into it.

 

[Sandy Feet]

One other thing I see is setting efficiency to 70 for a simple, single infusion BIAB. You probably need to bring that down a little, but that depends on the crush, too. I started having a little more luck with mine doing a 70-minute mash. That seems to work a little.
The OG @ 1.046 doesn't sound that far off from what I would expect with that much grain in BIAB. I try to make 19L (5 gallons) usually somewhere in the 5's for alcohol, and I would normally use more grain that that. My math has 4.18kg @ about 9 1/4 pounds, and that isn't much, especially using crystal.
If you are actually @ 1.022 it is going to be sweet. If it isn't, you might have a hydrometer problem.

 

[HighVoltageMan!]

You mashed kind of hot, and kind of short.

I think at that temperature the mash duration was fine. At lower temperatures the mash should be extended, but at 154F the enzymes are very active and the duration can be shortened.

 

[dmtaylor]

I think at that temperature the mash duration was fine. At lower temperatures the mash should be extended, but at 154F the enzymes are very active and the duration can be shortened.

True! It was the temperature that killed the beta amylase then. The time didn't matter so much. True.

 

[Bigbre04]

I would consider standardizing as many variables as you can. a 1 hour mash is very standard. shortening it doesnt save much if the beer doesnt turn out as expected.

I dont mess with different temps very often.

On the larger side of things we did change mash temps, but that was really only when we did stouts or big sticky beers. Generally speaking getting a consistent clean fermentation was preferred. for 80% of our beers we were mashing between 147-149. our stout we ran at 152-154. this was a very different setup(4vessel 30bbl newlands) so we had very fine control, grist hydrator, mash mixer, steam, etc.

on my tiny setup, i stay at 149 for everything since its allows for clean consistent repeatable beers. i can change my final sweetness by adding or removing ingredients.