failing to hit final gravity levels

[wesasmith]

Hey HBT,

got a fairly complex question here. I've completed 10 brews now. Mostly IPA's, APAs, (2) porters, and one Hefe. I'm hitting great flavor combinations, and that's not main concern. But I am noticing a bit of a trend, that my brews are not attenuating to my desired FG's. I've only had two out of the last 5 batches (lets throw out the first couple batches because i was still too new to the game)

Notes
All grain batches
tend to mash from 149-154 depending on recipe
use 10 gallon mash tun with false bottom
make 2L yeast starters with stir plate, and add oxygen before pitching
I ferment most ales at 68-70 for 2 weeks in primary, then dry hopping in secondary.
I trend to keep my adjuncts and crystal malts below 6-7 percent.


I believe my next step would be to build a fermentation chamber, but havent had the chance to put the pieces all in place.

Let me know if there may be something I'm missing

 

[Black Island Brewer]

The first thing that pops into my head is that maybe 2 weeks isn't enough. Are you judging the timing of your secondary by a stable gravity reading, or by the calendar? Perhaps it's just not finished when you move to secondary?

The second thing that pops into my head is that attenuation will vary by yeast strain, so your expectations might be out of sync with what the yeast can actually do.

 

[wesasmith]

Two weeks is more an average, I do take readings while still in primary, one about two days before then once again before racking.

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[BrewDawg79]

How far off are we talking? Two point high? Ten points high? Are you reading final gravity with refractometer or hydrometer? Lastly, you mentioned fermentation temps but then said you don't have a ferm chamber. Are your ferm temps beer temp or liquid temp?

 

[wesasmith]

Alot of my beers are finishing at the 1.020 range, when I'm hoping to end round 1.015-12. So about 7 points or so

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[IL1kebeer]

You mentioned that you didn't have a ferm chamber. How do you control temps now? Everything else that you are doing seems to be in favor of great yeast health; however, it's rather difficult to say that the temperature of your fermenting beer is absolutely controlled unless you have a chamber and a controller. Maybe your yeast are floculating early after the main part of fermentation is over and temps inside the fermenter drop. You need to be able to prevent any sort of drop in temp after this stage or your yeast will go to sleep before they chew through those final gravity points.

Other than that, what yeast are you using?


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[wesasmith]

I've experienced with wyeast 1028, 1098, and 1056.
I'm having some difficulty bumping the temp up late in the primary fermenting stage, which may be causing the yeast to drop out early. I usually wrap with a blanket and use a heating pad, or wet towel and fan when I need the temp to stay down.

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[Gameface]

Have you verified that the thermometer you use to gauge mash temp is accurate?

Temp drops (think of how cold it gets in the place where your fermenters are overnight) trigger dormancy in the yeast. During the most active phase the yeast are probably soldering on through some temp drops, but later on, when the food supply is starting to run a little short, they may just call it a day and rousing them back up, especially in a more alcohol rich and food supply lean environment, can be very difficult. Pitching more yeast doesn't solve the problem, as even a large pitch is less than what's already in there. The environment just isn't all that hospitable any more. Motivation on the part of the yeast wanes.

 

[BrewDawg79]

Have you verified that the thermometer you use to gauge mash temp is accurate?

+1 to accurately measuring mash temps. Once I really got into brewing I discovered that I have trust issues with thermometers. I finally bought a themapen in hopes to put my mind at ease. You mentioned that you have mashed at a range of temps and have had success with some beers finishing on target. Do you find that the beers mashed at lower temps hit your target fg while the beers mashed at the higher temps finish high? If so, look to the thermometer as a potential culprit.

 

[duboman]

First off, final gravity is basically a guess as there are various factors involved to achieve good attenuation.

Apparent attenuation can be calculated by the following: [(og-fg)/og-1] x 100 for your percentage of apparent attenuation. Compare this to the yeast manufacturer for each strain.

The second thing to look at is the calibration and accuracy of your thermometer. In many cases they are off and you might be mashing at a higher temp than you think. This will produce a less fermentable wort meaning less attenuation than desired.

Third, recipe formulation. I large percentage of less fermentable grains like crystal or other additives like malto-dextrine or lactose will produce a less fermentable wort.

Fourth would be mash pH being in the ideal range of 5.2-5.4 for proper conversion and extraction.

Since several of your recipes are IPAs and such my guess is an off thermometer for mash temps. Also the use of starters for liquid strains or rehydrating dry yeast. Proper aeration and good temp control will all be good things to add to your process if not being done already.

 

[Schemy]

I'll second, third and fourth the suggestion regarding your thermometer. When I was having similar issues, that ultimately was the deciding factor. I was mashing way too high, and just didn't have the fermentables. I now have two thermometers I use on brew days. One is a thermapen and the other a standard analog stainless thermometer. I try to calibrate before every brew day.