Struggles with FG.... Is it a yeast or mash issue?

[catalanotte]

I have had two batches now where I am way over my target FG. Both were mashed a bit hotter due to low FGs of a couple prior batches. These were mashed around 154. All other aspects have been about the same between the brewing process, including cooling, pitching, yeast starting, etc. I have produced two prior all-grain batches with same equipment and methods that fermented well and actually ended up a bit below desired FG.

Both batches started up within 4-8 hours, achieved good active fermentation for 3-4 days, then slowed to a crawl for a week. Both started at 1.056, one is at 1.024 the other 1.034. Separate brews, same OG is a coincidence,

Am I out of fermentable sugars due to the mashing process or have the yeast quit on me?

Was thinking about an experiment by making 2 starters, one with the high FG wort and new yeast, and another with good DME wort and the existing yeast cake. Does this sound like a good way to figure out what is going on here?

Could an increase in mash temperatures from 151 to 154 cause this large of an impact on fermentable sugars?

 

[itchygomey]

I highly doubt 3 degrees mash temp would make a huge jump in FG. That said, we need more info -

What yeast? How are you measuring temp? What is the recipe? What is the temp of the beer during fermentation? How are you measuring gravity?

 

[LLBeanJ]

Am I out of fermentable sugars due to the mashing process or have the yeast quit on me?

Not sure. It could be either. I suspect it is the former, though. At what temp are you fermenting? What yeast are you using and what is the starter size? Active fermentation beginning within 4-8 hours suggests possible overpitching, which wouldn't cause this problem.

Was thinking about an experiment by making 2 starters, one with the high FG wort and new yeast, and another with good DME wort and the existing yeast cake. Does this sound like a good way to figure out what is going on here?

I don't know if this will tell you what you want to know.

Could an increase in mash temperatures from 151 to 154 cause this large of an impact on fermentable sugars?

No. The difference in FG with that range of mash temps should only be a few points. How confident are you in the accuracy of your thermometer at mash temps? Your problem looks to me like it might be mashing at a much higher temp than you think. You're not using a refractometer to measure your FGs, are you?

 

[catalanotte]

I'll try to provide as much of the additional information that is needed as possible.

Using floating dairy thermometer, checked recently in a ice bath and boil to be accurate within .5 degrees. For an accurate mash temp, I leave in in the mash with the lid shut then check after a few minutes. I leave in in during the mash, and check again at the end to determine the temp drop in the tun.

Temps also matched up pretty good with strike water calculator predictions. 11 pounds at 1.25 qt/gal, used 169 water and got 154 degree mash. Mash out water temp calculator also got me within 1 degree of target (167).

I AM using a refractometer (recent change from a floating hydrometer) to measure FG. Is this a problem?

Both batches in question were about 1.056 OG (11 and 12 pounds of grain), one has slightly better efficiency.

Batch 1: Wheat beer
5 lbs 2-row
5 lbs Wheat malt
1 lb Dark Munich
OG 1.056
Wyeast 1010 - full swell on normal smack pack, very active fermentation within 12 hours, krausen all the way through blow off hose. Temp was around 74 for first coupe of days, then slowly dropped to cellar temperature of about 66 degrees. I did move this one to a slightly warmer room (72 degrees) for a couple days to see if that would help, no change.

Batch 2: Strong Pale Ale]
9lbs 2-row
1.5 lbs Crystal 40
1.5 lbs Carapils
OG 1.057
Repitched a washed yeast (1st reuse of a Wyeast 1056 for a batch that fully attenuated from a 1.051 to a 1.006, only 10 days old). Made a pint of starter, cell count may have been slightly low 160B but pitched an active starter, had steady fermentation within about 12 hours, but only about 2 inches of krausen. Very active for a couple of days then flattened out. Same general temps. Held about 75 for a couple of days, then dropped to 66 as it slowed down.


Fermentation temperatures have been the same for a few other recent all-grain batches without issue. (FG of 1.010 and 1.006).

 

[itchygomey]

Yes - Using a refractometer post fermentation will result in a skewed reading due to the alcohol present. Do you still have your hydrometer?

 

[catalanotte]

I do still have the hydrometer.

I just started using the refractometer for these last two batches that are giving me fits. I was reading up on a few discussions of the FG issue with refractometers after your comment cave me cause for concern. It would have been nice if the guys at the LHBS that sold this thing mentioned this little detail..... Although it has been awesome for monitoring sparge efficiency and OG pre/post boil.

Is the error large enough that I would be getting a 1.024 reading on a beer that has fermented out from a 1.056 OG to near a 1.012 FG (which is close to target) and yield about 5.7% ABV?

The calculators I have found look like they require both a refractometer reading in Brix and an SG reading from a hydrometer to calculate the ABV. Is the refractometer any use to get a FG reading or do I need to dunk the old fashioned hydrometer?

 

[itchygomey]

I cannot speak from experience as I don't use a refractometer post fermentation. I do use one to check pre and post boil gravity, but I use a hydrometer for post checks. My understanding though is yes, the error is significant.

 

[catalanotte]

I just found the calculator on www.brewersfriend.com for refractometer correction and If my numbers are right, a refractometer reading of 6 brix (1.024) as a FG with an OG is 1.056, should work out to a corrected FG reading of 1.010. Time to go home and see what I actually have.

 

[catalanotte]

I cannot speak from experience as I don't use a refractometer post fermentation. I do use one to check pre and post boil gravity, but I use a hydrometer for post checks. My understanding though is yes, the error is significant.

Compared online calculators of refractometer Brix to FG corrections to actual hydrometer readings and came within .002 on both beers.

Thank you to itchygomey for pointing this out. This was problem. Both beers finished perfectly, one at 1.013, the other at 1.011. Both are resting peacefully in secondaries waiting for keg space.