Low Attenuation- Grain Bill or Mash Temp or Yeast?

[micraftbeer]

I've made a Baltic Porter recipe a few times, and I keep getting a low attenuation in the fermentation (the "Apparent Attenuation" that Brewfather calculates). I see it come through as higher than predicted FG. The recipe originated from a BEERMKR Kit. That's a whole other story, but I made the beer there first and it seemed delicious, but I couldn't get the built-in dispensing kit to work so I was only ever able to get one pint out of it. And the BEERMKR is not set up for taking any kind of measurements of gravity, so I have no idea what kind of numbers I got using this recipe in that machine.

I carried the recipe over to my AG setup and scaled it up from the 1-gal BEERMKR size. It attenuated poorly, and I blamed it on what seemed to be an extremely high amount of specialty grains. So I adjusted the recipe to add a dose of Brewer's Malt, but still got low attenuation. I then brewed a 3rd time, and pitched more yeast, thinking I had underpitched on the 2nd batch. But it came out the exact same. I've used this yeast before (Cellar Science Berlin) with great results in various lagers and gotten good attenuation (70+ %).

So I'm not sure if I've got something funky with the grain bill that's driving the attenuation, or maybe it's this yeast coupled with the higher mash temperature. The other batches where I've gotten 70+% attenuation have been mashed at 148F, and this Baltic Porter I was mashing at 154F. I know the higher temp will give me lower attenuation, but it seems like a big drop off to be at 55%. Here's the details:

Batch#241 Baltic Porter
Munich 33%
Vienna 33%
Carafa Special II 11%
Caramunich III 11%
Special B 11%

Mashed Munich and Vienna to the below schedule, then added Carafa, Caramunich, and Special B at Mash out
156F for 45 mins
168F for 10 mins
Measured mash pH 5.5 (20+ minutes in to mash, sample cooled to room temp before measurement)

1 pack Cellar Science Berlin (no starter, no re-hydrating)
52F for 4 days until Tilt showed rate of gravity change start to slow, then slowly raised temperature

OG 1.061 (low by 11 points, which is very uncommon for me)
FG 1.027 (high by 5 pts vs where Brewfather was predicting)
Apparent Attenuation 54.5%

Batch#272 Baltic Porter
Brewer's 2-row 32%
Munich 22%
Vienna 22%
Carafa Special II 8%
Caramunich III 8%
Special B 8%

Mashed Brewer's, Munich, and Vienna to the below schedule, then added Carafa, Caramunich, and Special B at Mash out
154F for 50 mins
168F for 10 mins
Measured mash pH 5.29 (20+ minutes in to mash, sample cooled to room temp before measurement)

1 pack Cellar Science Berlin (no starter, no re-hydrating)
55F for 4 days until Tilt showed rate of gravity change start to slow, then slowly raised temperature

OG 1.071 (low by 6 points, which is very uncommon for me)
FG 1.031 (high by 16 pts vs where Brewfather was predicting)
Apparent Attenuation 54.8%

Batch#276 Baltic Porter
Brewer's 2-row 32%
Munich 22%
Vienna 22%
Caramunich III 8%
Special B 8%
Carafa Special II 6%
Carafa Special III 2% (misplanned, ran out of Special II...)

Mashed Brewer's, Munich, and Vienna to the below schedule, then added Carafa, Caramunich, and Special B at Mash out
154F for 50 mins
168F for 10 mins
Measured mash pH 5.25 (20+ minutes in to mash, sample cooled to room temp before measurement)

2 packs Cellar Science Berlin (no starter, no re-hydrating)
55F for 4 days until Tilt showed rate of gravity change start to slow, then slowly raised temperature

OG 1.072 (low by 4 points, which is very uncommon for me)
FG 1.032 (high by 17 pts vs where Brewfather was predicting)
Apparent Attenuation 54%

 

[RM-MN]

First place I would look is the thermometer you used to be sure it is really reading correctly. If you are trying to mash at 156 but your thermometer is reading low by 4 degrees, you were mashing out instead of mashing.

 

[micraftbeer]

I had two thermometers corroborating each other. One was in my RIMS, just before recirculation back into the kettle, the other was in my mash tun. (And when I say RIMS, it's actually a Blichmann Surface where the heating element is in the bottom of the mash tun, I just have the control temperature sensor in the recirculation loop because otherwise temperature reading from the mash was too unstable and would get overshoots.)

I was wondering about temperature being too high as well and after the first batch at 156F, I lowered the following ones to 154F just to give me more margin.

 

[dmtaylor]

Maybe the yeast is $h!t. Try S-189 or Diamond instead.

I agree about the thermometers also. Check all your thermometers in freezing water and boiling water corrected for your elevation above sea level. Maybe both/all are off by a few degrees, who knows.

 

[keystonehb]

With your thermometers being correct I would think it is more than likely your mash temp. If I want my beer to attenuate as much as possible I usually mash at 149. If I want some residuals leftover I mash at 152. In beers with similar recipes and the same yeast strain I've seen a 2-5 point difference.

Also While it might not change thing much, by adding those grains late in the mash you lose some potential sugar. By adding them to your recipe it assumes that you are mashing for a longer period at the lower temperature. Since you are not I t would throw your numbers off. I'm not sure if there's a setting for adding grains to mash out in Brewfather. Just a thought

 

[doug293cz]

Your mash times seem a bit short to me, unless you are monitoring the SG in the mash and know that you have reached max SG for your grain bill and strike water volume. Are you monitoring the SG of the wort during mashing?

Brew on

 

[micraftbeer]

Your mash times seem a bit short to me, unless you are monitoring the SG in the mash and know that you have reached max SG for your grain bill and strike water volume. Are you monitoring the SG of the wort during mashing?

Brew on

I do not monitor it. But a great question sending me to ponder that which I thought I "knew"... Somewhere along the line, I had in my mind that at lower mash temp I needed to mash longer to get full conversion, but at higher mash temp I could mash shorter. Your question made me go think about where I came across that belief. Couldn't find it.

My typical process is 150-152F I mash for 60 min, 145-148F I mash for 75 min, and 156F I mash for 45 min.

In trying to figure out this attenuation thing, I searched some other posts, and someone in another thread pointed to a Braukaiser set of experiments that I've been working my way through reading & digesting (http://braukaiser.com/documents/Effects_of_mash_parameters_on_attenuation_and_efficiency.pdf). With @doug293cz question, I popped over to that and found this relevant plot:

This shows me that although the higher mash temp has higher conversion efficiency, it doesn't reach it's max potential until about the same time in of the mash. And the higher mash temp has a higher rate of change during the start of the mash. So after looking at this, I think I'll reconsider my mash time protocols...

 

[Bassman2003]

It is a learning process. Since you are interested in attenuation, I will give my perspective. Think of Beta and Alpha as being two different kinds of gravity. Beta leads to lower attenuation where Alpha leads to overall conversion and gravity. Confused? Mashing is really a plan you execute for the beer qualities you want in the finished beer. They say Bud Light is/was mashed at 147F for 5 hours. Why? Because the plan for that beer is to be as light, dry and drinkable as possible. So how does this apply to our beer?

Well, plan your mash. If you want a beer that is well attenuated, you need to involve Beta. Period. If you mash at 154F Beta is pretty much out of the picture. Since you are doing a few rests already, I would advise to do a Hoch-Kurz mash schedule for every beer. This is usually 148F/160F/172F. While all of the rests are touched upon, you determine how long to stay in them.

On the topic of time inside mash rests - track your gravity through the mash. If you have a refractometer, take a reading every ten minutes during your mash. Have targets to reach before moving on to the next rest. This ensures that you will never reach the boil kettle until you get what you set out for. You will learn a lot and might be surprised how long you need to hang around to reach your goals. For lager, I like to get 90% of my pre-boil gravity in Beta. Yes, it takes a while but that is how you get good attenuation.

Imho, homebrewers favor Alpha too much which results in flabby beers. Shooting for 80%AA is a good goal for a lot of beer. Hope this helps!