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Brewing Topics => Brew In A Bag (BIAB) => Topic started by: bubba931 on August 16, 2017, 01:51:08 PM

Title: BIAB gravity too low.
Post by: bubba931 on August 16, 2017, 01:51:08 PM
I just put my third BIAB brew in the fermenter and the OG is off by a least 10 points. The only thing I can figure I'm not stirring long enough or vigorously enough when I put the grain bag in my mash tun. I mash in my insulated cooler and then do a full boil in my kettle. I'm doing 5 gallon batches and my thermometers are all correct and calibrated. I'm not new to brewing, I started extract brewing in 1992 and graduated to all grain 10 years ago.

Thanks in advance.

"The mouth of a very happy man is full of beer."
Title: Re: BIAB gravity too low.
Post by: Oginme on August 16, 2017, 06:11:33 PM
Was it just this last one that is off, or have all three of the BIAB brews been off in OG?

Generally, if you just switch from conventional mash tun brewing to BIAB, there will be a drop off in efficiency due to the lack of a clean sparge.  This difference can be easily made up by grinding your grains a little tighter.  I typically achieve a mash/lauter efficiency (BeerSmith shortens this to 'mash efficiency') of around 86% to 87% for most brews. 

I've found the best consistency in doing BIAB is to stir the grains in for at least five minutes.  I typically do ten.  It does not have to be a "beat the crap out of the grains" stirring, but it can't be a passive "flop the spoon around a bit" type of stirring either.  The objective is to make sure you have all the dough balls completely broken up and the grains fully dispersed.  I usually stir with an upwards motion to bring any clumps of grains from the bottom of the bag up towards the surface where I can see them and mash them up against the side of the kettle. 

You mention nothing about pH.  This could also affect the conversion rate, but if you are mashing for an hour or more, it is usually not an issue.

Hope this helps some.
Title: Re: BIAB gravity too low.
Post by: bubba931 on August 16, 2017, 09:19:38 PM
Actually all three have been off, so my assumption that I'm not stirring enough is probably true. I've never had a problem with pH before so I never mentioned it.

We'll see what happens with my next batch, I hope to be doing one in a week or so.

I guess it's just part of the learning curve with a new method for me.

Thanks for the input.
Title: Re: BIAB gravity too low.
Post by: Oginme on August 17, 2017, 05:05:13 AM
Since all three have been off, I would recommend adjusting your brew house efficiency to match your last three results.  Stirring usually results in inconsistent efficiency.

Depending upon you actual mash efficiency, you may want to look at crushing your grains a bit finer.  With BIAB there is really no chance of a 'stuck mash' unless you go to a full grind to flour or use a significant amount of hull-less grains such as wheat or rye.
Title: Re: BIAB gravity too low.
Post by: Kevin58 on August 17, 2017, 11:44:29 AM
Lower the mash efficiency numbers in your program for the time being. I had to lower mine to 60% when I first started BIAB. This means you will need to increase your fermentables slightly to reach your target OG but that's OK.

You can leave it at that or you can try crushing your grains a little finer. If you have a grain mill and it is set up fora  typical crush the gap between the rollers is probably about "credit card" thickness... or about 0.038". Reduce the gap to somewhere between 1.025 to 0.030. That should increase your percentage then you can adjust your mash efficiency number in your software accordingly.

As for stirring, I stir for the first five to ten minutes. Not vigorously but I want to make sure there are no dough balls. Then I stir a bit every time I check the mash temp which is about every 15 minutes. I do this not so much for efficiency but just to make sure I get an accurate temp reading.

Title: Re: BIAB gravity too low.
Post by: bubba931 on August 17, 2017, 02:00:38 PM
I have done as you have suggested and we'll see how it goes going forward. I set the efficiency at 60%, that looks like where it should have been based on the amount of grain I used and where the OG came it at.

On the last batch I did crush the grain finer but that didn't seem to help much.

As I mentioned earlier there is probably a learning curve here. I don't bother checking the temperature as I mash in my insulated mash tun and then transfer everything to my boil kettle.
Title: Re: BIAB gravity too low.
Post by: BrewSmilee on November 12, 2018, 10:35:11 AM
I know this is an old thread, but I am having exactly the same. 

Curious, how did the adjustments work out for you?

Title: Re: BIAB gravity too low.
Post by: bubba931 on November 12, 2018, 11:13:43 AM
I was better after I made the adjustments, but my brew seemed to tasted "washed out". The biggest thing I did after that was invest in a Robobrew in March of this year and have been using that since.  I've got 12 brews through it so far this year and all my numbers are good. BIAB was an experiment that didn't work out too well for me, others rave about it.

The Robobrew had a learning curve as well and some alterations to some profiles but I really prefer my all in one pot to BIAB. Just my 2 cents.