BIAB Attenuation Issues: Fact or Fiction?

[NWMushroom]

Did anyone else read the Mr. Wizard section in December's Brew Your Own Magazine?

For those who haven't, here's an online link (second question down):

https://byo.com/stories/issue/item/3188-tropical-brewing-mr-wizard

The question features a BIAB brewer who complains about under-attenuation. Mr. Wizard answers by blaming the higher water volume in BIAB, stating that (edited for brevity in this post):

When mashes become progressively thinner, enzyme stability decreases... The rate of the enzymatic reaction is also slower because the concentrations of both enzyme and substrate are reduced as the mash becomes more diluted... This has a direct bearing on your particular problem, and that problem is low wort fermentability... The result is a high finish gravity.

I have to say that in over a year of BIAB brewing, I've not had any issues with under-attenuation and I haven't adjusted my mash temperatures either. I put the full water volume in the mash - just like the person who wrote in to Mr. Wizard.

Does anyone else notice issues with (or account for) under attenuation/low wort fermentability with BIAB?

If not, has the theory shared by Mr. Wizard been debunked?

 

[dfhar]

Total fiction. You've proved that yourself with your year of successful BIAB brewing.

The one and only time I ever had an underattenuated beer was when I didn't oxygenate enough before pitching my yeast.

BIAB gets a lot of bad press that it doesn't deserve. The amylases work just fine in a thin mash. Squeezing the bag doesn't extract tannins.

One thing that can actually be a problem with BIAB is mash pH. I don't hear many people talk about it though. If you were mashing 6 pounds of grain in 9 quarts of water (1.5 qt/lb is a pretty typical mash thickness) and had a mash pH of 5.4, adding an additional 11 quarts of RO water (20 quarts of water and 6 pounds of grain would be typical for a moderate strength 3.3 gallon BIAB batch, assuming a mash efficiency in the low-mid 80s and a 90 minute boil) would raise your pH to 5.75 because you've just diluted the acids in the mash. Alpha amylase will work just fine at 5.8, although beta amylase will work more slowly. 5.8 is an acceptable mash pH, but some people do claim that a mash pH in the 5.8 range leads to a "duller" malt flavor than the 5.2-5.4 range. Of course, if your water is alkaline then your pH will be even higher than 5.75. If your pH exceeds 6 I can see some problems happening like incomplete conversion, tannin extraction, etc.

The long short of it is that BIAB is just fine assuming you have low to moderate alkalinity water. If you have very alkaline water, then you can consider acidifying the mash and/or mashing thicker.

I do BIAB as well, but I typically mash at 2 quarts per pound. This way, I find it easier to keep my pH between 5.2 and 5.4 without having to add much acid. After conversion is complete, I top off the mash with enough extra water to reach my desired pre-boil gravity, then I pull and squeeze the bag.

 

[Magnus314]

Does anyone else notice issues with (or account for) under attenuation/low wort fermentability with BIAB?

My results have been the exact OPPOSITE: too high attenuation / too low FG.

Without being 100% sure why, it seems like the fine grind allowed by BIAB style brewing combined with standard non-BIAB mash times made for high attenuating mashes.

My last several batches I went with shorter mashes (30 minutes) and my attenuation has been much better- around 80% each time.

And to add to what dfhar said, I have gotten a sour twang in very light beers (like an all Pilsner Malt smash) that I attribute to mash pH issues.

I've done the exact recipes since, except I held back some water for a sparge (and now I do a pour over sparge) instead of full volume and did not have any issues and no "twang".

 

[RM-MN]

My results have been the exact OPPOSITE: too high attenuation / too low FG.

Without being 100% sure why, it seems like the fine grind allowed by BIAB style brewing combined with standard non-BIAB mash times made for high attenuating mashes.

My last several batches I went with shorter mashes (30 minutes) and my attenuation has been much better- around 80% each time.

And to add to what dfhar said, I have gotten a sour twang in very light beers (like an all Pilsner Malt smash) that I attribute to mash pH issues.

I've done the exact recipes since, except I held back some water for a sparge (and now I do a pour over sparge) instead of full volume and did not have any issues and no "twang".

Same here, even with a 20 minute mash and Windsor yeast I got something like 80% attenuation. I'll try an even shorter mash a few times to see if that helps although the last batch where I used a refractometer to check, I was still gaining sugars until the 25 minute mark. Since I have been seeing high attentuation and wanted a little body left in that beer I added lactose which may not be the answer.

 

[TexasWine]

Ditto. Over attenuation has been par for the course for me. Even with a 30 minute mash.

 

[beersk]

I had underattenuation issues in the past, it was when I applied direct heat to the kettle to stabilize mash temp and measured the temp near the top of the mash. Bad idea. The mash was likely 175F near the bottom (this was on an electric stove) and killing enzymes. Every beer, no matter what, was stopping short at 1.020. As soon as I stopped applying direct heat and insulating the kettle with a blanket, that issue went away.
I have had more issues with fermentation without krausen with BIAB than my usual setup with a cooler and batch sparging.

 

[Seven]

My BIAB brews attenuate just fine. I had one or two that didn't fully attenuate when I first started brewing but I have since learned the error of my ways.

 

[QuercusMax]

I haven't noticed any attenuation differences between BIAB and traditional 3-vessel, but I never did a full-volume BIAB mash. The pH thing seems like something to watch out for, which is one reason I never messed around with full-volume mashing.

 

[hawktrio]

I have been plagued with under attentuation issues with BIAB but I actually think I have been boiling too hard (2400W element + 2 gas stovetop burners) for too long (90mins) and that it's not my mash. Could this be my problem? My first 3v blonde got down to 1010 in a week but it only had a gentle boil (2400W element only) for an hour. Too many changes I know. I had always boiled hard after listening to the BN but we'll see how this blonde turns out.

 

[wobdee]

All my full volume BIAB brews seem to turn out a few points high but never thought it was due to thin mash. I think it may be aeration problem or inaccurate mash temps. I'm going with pure O2 now so I'll see what happens.

 

[mb82]

My first few batches were a few points high. Once I figured out my thermometer was off they have been dead on the money since.

 

[hawktrio]

I've been using pure O2 all along so that is not my prob.

 

[NWMushroom]

Thanks for chiming in guys, glad to see I'm not the only one that hasn't noticed BIAB causing under attenuation. Odd that such a new article in BYO Mag preaches otherwise. All the science-y words Mr Wizard used sure sounded convincing!

 

[hawktrio]

The temp idea could be on the money. With a full volume mash the temp of the water measured by hand (e.g. Thermapen) at the top of the liquid is likely to be slightly cooler than that at the bottom where the grain settles.

 

[ArkotRamathorn]

Complete fiction.

I actually have more issues with OVER attenuation. Single packet of S04 I regularly get 80-85% apparent attenuation (rated at an average of 72%). I had to mash a scotch ale at 158 with decoctions to get S04 to actually stop at the rated average of 72%.

 

[beersk]

The temp idea could be on the money. With a full volume mash the temp of the water measured by hand (e.g. Thermapen) at the top of the liquid is likely to be slightly cooler than that at the bottom where the grain settles.

Possibly, but if you're stirring while taking the temperature, then that shouldn't be an issue.

And, I don't think boiling hard would be cause for attenuation issues. It has to be something else.
Don't apply direct heat unless you're recirculating your mash.

 

[soccerdad]

I have had only one or two circumstances of under attenuation with BIAB - and I have thought each time that I had under-pitched. Otherwise I have been over or spot on. I'll look at it more closely after reading this, but I think the article writer is dealing with unsupported myth. MYO

 

[Twang]

From BrauKaiser

water to grist ratio: the enzymatic activity of the amylases is affected by the thickness of the mash. However, during the Limit of attenuation experiment it was observed that mash thickness has no significant impact on the fermentability. This is likely the result of a balance of two factors: thin mashes cause enzymes to be denatured faster but they also cause enzymes to work more efficiently, thus being able to produce the same amount of fermentable sugars even though they aren’t active as long.

 

[Siberian]

From my last few batches (sorted by Yeast Type) these are repitches except the first batch in each list. I'm either top cropping and repitching or re-using slurry to provide the yeast multiple beers in a chain. I don't like growing up huge starters to make big beers, I'd rather grow yeast in a small beer and then make bigger beers from it.

White Labs German Bock Lager WLP833 - Expected Attenuation 70-76%

• Marzen/Oktoberfest: 1.055 OG - 1.012 FG - Apparent Attenuation 77.3%
• Doppelbock: 1.072 OG - 1.015 FG - Apparent Attenuation 78%

White Labs Dry English Ale WLP007 - Expected Attenuation 70-80%

• Extra Special Bitter: 1.049 OG - 1.015 - Apparent Attenuation 69.7%
• Winter Warmer: 1.067 OG - 1.016 FG - Apparent Attenuation 74.6%
• Strong Scotch Ale: 1.069 OG - 1.014 FG - Apparent Attenuation 78.6%
• Stout: 1.055 OG - 1.013 FG - Apparent Attenuation 75%

I don't see anything in these numbers to me that would indicate I'm finishing too high or having low attenuation issues, each falls within the styles I was targeting. I had one beer that finished a bit shy of the expected range of attenuation, but the ESB had about 8% crystal malt in it and was mashed on the higher side. Plus it was within the style range anyway (1.010-1.016) and I was looking for more body. Everything looks okay to me.

All of my batches a full water volume, anything with Pilsner malt in it (Oktoberfest/Doppelbock) means it gets a 90 minute boil so my mash is even thinner then the normal batches. The London Ale yeast batches are all Maris Otter based so 60 minute boils and a slightly thicker mash by comparison. Oktoberfest (13lbs of grain in 8.8 gallons of water) and ESB (10.3lbs of grain in 7.75 gallons of water) are the thinnest.

 

[jason91notch]

My attenuation has been better, if anything. The only issue I seem to have when doing biab is more trub loss. I whirlpool, filter when transferring, etc, but still always have ridiculous amounts of trub loss, and it's been hard to nail final volumes because of it. I'm starting to get it figured out though, and it's not that big of a deal anyway.

 

[danok1]

Complete fiction.

I actually have more issues with OVER attenuation. Single packet of S04 I regularly get 80-85% apparent attenuation (rated at an average of 72%). I had to mash a scotch ale at 158 with decoctions to get S04 to actually stop at the rated average of 72%.

This. I also get 80%+ with S-04. Took my last batch of stout from 1.055 to 1.009. Nope, no underattenuation here!