Still Trouble with Low FG

[Monmouth00]

Hello All,

My second batch on the eBIAB seemed to have gone well, but I'm still having trouble with low apparent attenuation.

I did a SMaSH IPA with Maris Otter and Mosaic. I was estimated at 6.1% ABV, but when I measured it still came in low at 5.22%

My post boil gravity was 1.060 (14.7 Brix) - right where I was aiming. I pitched the US-05 and fermentation got going normally after about a day. I kept the inkbird and mat set at 69 degrees, but after two days it crept up to 72. I figured vigorous fermentation caused the temp spike, so I took some of the insulation off and it came back down to the 68-69 degree mark relatively quickly. It continued to bubble for a few more days, then quit on about day 6.

I left it alone for another 5 days, cold crashed, and transferred to the keg.

My final gravity reading was at 8.8 Brix - which when plugged into Brewer's Friend and Beersmith, only gives me about 5.22% ABV and 63.8% attenuation.

I may have messed up by not taking a gravity reading before kegging, but I was nervous about getting O2 into the fermenter, so I assumed I was fine after 11 days - having read that's plenty of time for US-05 to finish.

What did I do wrong? Am I still not getting this refractometer thing right?

It's going to be drinkable beer - it looks, smells, and tastes delicious. I'm just frustrated that two brews have missed their target FGs.

Thanks for any wisdom you can impart.

 

[jrgtr42]

Did you use the calculator for the refractometer - it doesn't read correctly after fermentation, due to the alcohol, so you have to plug it into a formula. Ideally you'd find a specific adjustement for your rig.
When I got mine, I would back up the FG readings with my hrdrometer, for the first half dozen brews at least. Once I got used to it, I'll just plug it into the calculator. I do back check every few batches to make sure, but it's close within a point or two - close enough for my notes.

 

[VikeMan]

My final gravity reading was at 8.8 Brix - which when plugged into Brewer's Friend and Beersmith, only gives me about 5.22% ABV and 63.8% attenuation.

Yeah, that sounds pretty low. What were your mash temp and mash length? And regarding the mash temp, how are you measuring that, how sure are you of its accuracy, and is there any heating involved after mash-in?

 

[Yooper]

What is the corrected FG? It sounds like you think it may be too high and not too low?

 

[Alan Reginato]

I use this calculator:
https://www.petedrinks.com/abv-calculator-refractometer-hydrometer/Check it out.

 

[Monmouth00]

Did you use the calculator for the refractometer - it doesn't read correctly after fermentation, due to the alcohol, so you have to plug it into a formula. Ideally you'd find a specific adjustement for your rig.
When I got mine, I would back up the FG readings with my hrdrometer, for the first half dozen brews at least. Once I got used to it, I'll just plug it into the calculator. I do back check every few batches to make sure, but it's close within a point or two - close enough for my notes.

Yes, I used the refractometer calculator on Brewer's Friend. I haven't used my hydrometer since I got the refractometer. It's supposed to be easier and more accurate!

Yeah, that sounds pretty low. What were your mash temp and mash length? And regarding the mash temp, how are you measuring that, how sure are you of its accuracy, and is there any heating involved after mash-in?

60 minute mash at 152 degrees - or at least that's what I was shooting for. I have a thermowell at the bottom of the kettle that I set at about 154. I recirculate and stir through the mash with the inkbird controlling the temp, so it kicks the element on and off throughout. Long hoses make me lose a bit of heat, but it generally was measuring 154 at the bottom thermowell and about 150 where the arm was dumping the recirculated wort.

What is the corrected FG? It sounds like you think it may be too high and not too low?

Corrected final gravity (14.7 Brix to 8.8 Brix with a 1.0 correction factor) was 1.021

 

[Monmouth00]

I use this calculator:
https://www.petedrinks.com/abv-calculator-refractometer-hydrometer/Check it out.

Thanks for that. Very similar to the Brewer's Friend calculator.

This one gives me a slightly higher FG of 5.3% - but still off from the 6.1% ABV I was expecting.

So, anybody have any idea where I screwed up?

 

[Yooper]

I’m suspicious of the last refractometer reading- can you grab a hydrometer reading, to make sure your refractometer is calibrated and your wort correction factor is correct?

 

[Monmouth00]

I’m suspicious of the last refractometer reading- can you grab a hydrometer reading, to make sure your refractometer is calibrated and your wort correction factor is correct?

Unfortunately, the beer is under pressure in the keg right now, carbonating. I cannot grab another sample.

I do, however, check that the refractometer is calibrated by putting distilled water on it and making sure it reads 0.0

Regarding wort correction factors - how do we calculate those? I have heard anywhere from 1.0 to 1.04 is standard. Not a lot of deviation there.

 

[Miraculix]

Unfortunately, the beer is under pressure in the keg right now, carbonating. I cannot grab another sample.

I do, however, check that the refractometer is calibrated by putting distilled water on it and making sure it reads 0.0

Regarding wort correction factors - how do we calculate those? I have heard anywhere from 1.0 to 1.04 is standard. Not a lot of deviation there.

That's for wort, not for finished beer.

 

[madscientist451]

So, anybody have any idea where I screwed up?

Re-brew and dial back your mash temp from 154 to150? Another thing you could try is to mash in and get your mash temp where you want it to be, and then insulate your vessel and don't mess with it for an hour, come back and run your recirculation for a while. Keep trying different things, but try changing only one thing at a time, you'll eventually find a way that works for you.
Hey, it still came out as good beer, so enjoy life and celebrate!

 

[VikeMan]

That's for wort, not for finished beer.

The wort correction factor is used to adjust both the original and the final refractometer readings. The difference is that final reading is also adjusted for alcohol (informed by the original reading).

 

[VikeMan]

Long hoses make me lose a bit of heat, but it generally was measuring 154 at the bottom thermowell and about 150 where the arm was dumping the recirculated wort.

I wonder how hot the wort that is actually in contact with the element is getting. How close is your thermowell to the element?

 

[VikeMan]

Unfortunately, the beer is under pressure in the keg right now, carbonating. I cannot grab another sample.

Do you have a picnic tap? Or even a piece of tubing to connect to a liquid QD? If so, you could draw a sample, warm to your hydrometer's calibration temp, degas, and measure.

 

[Monmouth00]

The wort correction factor is used to adjust both the original and the final refractometer readings. The difference is that final reading is also adjusted for alcohol (informed by the original reading).

So my process is this:

After boil, I use the refractometer to get the SG - in this case the 1.060 I measured.
I use the Brewer's Friend Calculator ( Brix Conversion Calculator | Brewer's Friend ) to convert to Brix. (I'll plan on just reading Brix in the future and not converting)
After primary and before kegging, I take another refractometer reading in Brix - this time it was 8.8
I use those two numbers in the Brewer's Friend calculator here: Refractometer Calculator - Brewer's Friend with the 1.0 or 1.04 correction factor.
OG Brix as 14.7, FG Brix as 8.8 - gives me 5.22% ABV

Do you see flaws in this process? Is there a step I'm missing?

 

[VikeMan]

Do you see flaws in this process?

Just one, which you already plan to correct, i.e. use the raw original brix reading in the calculator. If I were king for a day, I'd remove all of those "SG" scales from refractometers.

 

[yoop89]

Cheap refractometer or name brand? I ask because I had one in a lot of items I bought off someone that had a different SG scale vs the brix scale. When comparing the two refractometers side by side the brix reading were the same but SG was off anywhere from 3-5 points.

 

[jdauria]

Just to be clear, you are putting the 8.8 Brix in part II of the Refractometer calculator to convert it for the presence of alcohol? You have confirmed your refractometer reads 0 Brix with distilled water? Maybe mash lower than...154 at bottom, 150 at top, so you are assuming a 152 mash temp overall, but not sure? Another thing to look at, your yeast pitch...are you just sprinkling US-05 on the wort or rehydrating? Using Brewers Friend yeast calculator, at a minimum pro pitch rate...you would need to almost 2 packs of dry yeast. If you are underpitching, that could also lead to the beer not attenuating fully.

 

[Monmouth00]

Just to be clear, you are putting the 8.8 Brix in part II of the Refractometer calculator to convert it for the presence of alcohol? You have confirmed your refractometer reads 0 Brix with distilled water? Maybe mash lower than...154 at bottom, 150 at top, so you are assuming a 152 mash temp overall, but not sure? Another thing to look at, your yeast pitch...are you just sprinkling US-05 on the wort or rehydrating? Using Brewers Friend yeast calculator, at a minimum pro pitch rate...you would need to almost 2 packs of dry yeast. If you are underpitching, that could also lead to the beer not attenuating fully.

Yes:

Regarding mash temps, yes, I'm assuming 152 overall. I might try to set and forget on the next brew, but I really don' think the problem is with the mashing. I'm hitting the OG I want - within .001-.003 each time.

I did not re-hydrate the US-05. I've never done so in the past, going back 5-6 years of extract brewing. I've also never used more than one pack, as I rarely ever brew anything much higher than 6-6.5% ABV. The fermentation didn't look any different than anything I've seen in the past either - plenty of bubbles, healthy krausen, regular duration. Do you really think under-pitching could be the problem? I would be shocked if it is.

 

[Monmouth00]

Cheap refractometer or name brand?

This one - not overly expensive, but in line with others offered: https://www.amazon.com/gp/product/B01LW2ZU6R/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I did check with distilled water that it reads 0.0 - and I also confirmed that the SG-Brix conversion was accurate as compared to the Brewers Friend calculator.

 

[jdauria]

Yeah seems to be only 3 options...bad refractometer, mashing temp to high...or under pitching yeast. Just try pitching 2 packs of dry yeast next time and see what your attenuation is...if it's much better, then you know, if it's not...then it's probably the mash temp. I use liquid yeast, pitch at pro rates and always hit estimated FG, or go even lower than the estimate.

 

[VikeMan]

Regarding mash temps, yes, I'm assuming 152 overall. I might try to set and forget on the next brew, but I really don' think the problem is with the mashing. I'm hitting the OG I want - within .001-.003 each time.

So, hitting your target OG is a function of assuming the correct mash efficiency for your setup, and doesn't have much to do with temperature. Unless your mash temps are way off, OG will be fine. But mash temps can affect fermentability (and thus FG) significantly.

 

[Monmouth00]

So, hitting your target OG is a function of assuming the correct mash efficiency for your setup, and doesn't have much to do with temperature. Unless your mash temps are way off, OG will be fine. But mash temps can affect fermentability (and thus FG) significantly.

So, here's where the discrepancy with measured temps might lay - my thermometer in the thermowell near the elements (close, but not super close) is controlled by my inkbird PID. That reads 154 or thereabouts. I recirculate through the lid, and the measured temp there (with handheld digital thermometer that I've been told is very accurate) reads about 150, give or take. Stirring doesn't change that reading too much. So, I'm assuming that the temp being taken from the thermowell (close to elements and under a false bottom) is slightly higher than what's actually in contact with the grain. And I am recirculating constantly at a relatively high flow rate through the mash.

But, even if the 154 is correct, are you telling me that 2 degrees higher than my intended 152 mash temp (per recipe) is going to negatively affect the fermentability of the wort to the tune of almost a full % of ABV?

I know there is a lot of science involved in this stuff that is beyond my grasp as a beginner all grain guy, but this seems like a pretty severe penalty to pay for 2 degrees.

Plus - I should mention that my first brew (a Fat Tire clone mashed at the same temps) tasted thin - like my mash temps were too low.

 

[VikeMan]

But, even if the 154 is correct, are you telling me that 2 degrees higher than my intended 152 mash temp (per recipe) is going to negatively affect the fermentability of the wort to the tune of almost a full % of ABV?

No, I'm not talking about 2 degrees. I'm talking about maybe 5-6 degrees. This is not uncommon with RIMS and RIMS-like setups, where the actual temp of the wort in contact with the heating element is denaturing the enzymes in the wort faster than normal.

I don't know if this is your issue. But I would recommend calibrating your thermometers/probes to be sure (something I'd do occasionally even if I didn't suspect an issue).