First BIAB batch; really low pre-boil gravity

[moldmaker]

Today is my first BIAB batch. It's 5 gallons, and I have 12lb Maris Otter and 3oz Mosaic. I mashed with 7.5gal of water at 154-156F for 60 minutes and my pre-boil gravity is 1.020, well below the target of 1.057. That's measured with the hydrometer floating in the kettle at 154F. Here's my crush:


I got it crushed from the company I bought it from, but I didn't specify that I was brewing BIAB. It's way coarser than .025-.035". Could this be my problem? Am I measuring gravity wrong?

 

[AlexKay]

Floating the hydrometer in the kettle means you’ll have to correct for temperature — water is significantly less dense when hot.

But crush is a big deal with BIAB. I eventually got my own mill because of vendor-to-vendor and order-to-order variability. There are a few online stores that’ll double-crush your grain for you.

 

[hotbeer]

Is that 1.057 your OG or actually your pre-boil SG? Many of the recipes I find don't ever state anything but OG and FG which are not at pre-boil.

How much wort? 7 gallons of 1.020 wort getting boiled down to 4.5 gallons will give you a 1.57 OG.

OG is measured during the time after the boil is cooled and prior to pitching yeast.

If it is your pre-boil target as you stated, then what is your OG? That must be a pretty big beer.

 

[doug293cz]

Today is my first BIAB batch. It's 5 gallons, and I have 12lb Maris Otter and 3oz Mosaic. I mashed with 7.5gal of water at 154-156F for 60 minutes and my pre-boil gravity is 1.020, well below the target of 1.057. That's measured with the hydrometer floating in the kettle at 154F. Here's my crush:
View attachment 809136

I got it crushed from the company I bought it from, but I didn't specify that I was brewing BIAB. It's way coarser than .025-.035". Could this be my problem? Am I measuring gravity wrong?

1.020 at 154°F converts to 1.037 or 1.039, depending on whether your hydrometer is calibrated at 68°F or 60°F, respectively, according to this calculator.

12 lb of Marris Otter mashed in 7.5 gal of water should give a pre-boil SG of about 1.052 at 100% conversion efficiency. Your conversion efficiency, assuming your pre-boil SG was 1.038, comes out about 71%. Conversion efficiency in your mash should be over 90%, 95%+ is relatively easy to achieve, with a fine enough crush, long enough mash time, and mash pH in the range about 5.3 to 5.7.

Your low conversion efficiency is almost certainly primarily due to your coarse crush, for which you would need a significantly longer mash to get good efficiency (larger grits take longer to convert fully.)

Brew on

 

[Sammy86]

I mashed with 7.5gal of water at 154-156F for 60 minutes and my pre-boil gravity is 1.020, well below the target of 1.057.

Did you sparge at all or just mashed?

That's measured with the hydrometer floating in the kettle at 154F. Here's

I was going to say the same as @doug293cz but he beat me to it!

 

[doug293cz]

Did you sparge at all or just mashed?



I was going to say the same as @doug293cz but he beat me to it!

I assumed since OP said "mashed with 7.6 gal of water," that it was full volume no sparge.

Brew on

 

[AlexKay]

All that said, 71% efficiency isn't a game-ender -- you can make perfectly good beer with low efficiency! If your crush is consistent (big if) you can just adjust by spending a few dollars for a little more malt.

 

[moldmaker]

I mashed with the full volume of water; 7.5 gallons. No sparge.

The numbers I got came from the Brewfather app. 1.057 pre-boil and 1.065 OG, so I misread the 1.057 as OG earlier.

I ended up with 5.25 gallons after the boil. When I chilled it down to 60F, the OG reading was 1.054, much more inline with what I was expecting.

All that said, 71% efficiency isn't a game-ender -- you can make perfectly good beer with low efficiency! If your crush is consistent (big if) you can just adjust by spending a few dollars for a little more malt.

How is the 71% being calculated? Do I need to take pre-boil gravity at room temperature?

 

[balrog]

Use a hydrometer temperature calculator such as this one.
You will need to know what the "calibration temp" of the hydrometer is, typically printed on the little sheet of paper inside the hydrometer, typically either 60F or 68F.

 

[moldmaker]

That helped a lot, thanks. My hydrometer is calibrated for 60F. That means my pre-boil gravity was 1.039, still way off from 1.057.

I'm reading John Palmer's book, Ch 12 Mash Efficiency. According to the formulas given,

6.75gal pre-boil * 39 points / 12lb grain = 22 points
My grain's potential is 38, so isn't my mash efficiency 22/38 = 58% ?

I'm really getting turned around with the math my first time out here.

 

[palmtrees]

Brewers friend has a mash efficiency calculator that's very useful. You put in your grain bill, the amount of mash water, and your measured gravity. It will tell you the potential gravity and your efficiency.

71% isn't terrible. I have my own mill and grind the grain quite fine, and I often only hit 78-80% efficiency. I'm fine with that, and it still makes great beer! Someone above said you should be able to get 90-95% efficiency; in my experience, that's very hard to achieve without a ton of effort and process tweaking. In the 80s is easily doable with a good crush.

 

[balrog]

Frankly, I rarely adjust for SG after the mash. But I also have done similar recipes repeatedly rather than jumping all over the place.

To me, I want to look at FINAL volume into fermenter and that final volume's OG. That is my primary concern now that my process seems fairly repeatable. That's not to say I don't write down, graph, stew over, ruminate, cogitate and otherwise obsessively analyze many other data points of time temp weather gravity sunspots and fractalized poltergeists along the way. However, I want the recipe to give me a certain fermenter volume and a certain OG. So I really only look at Brewhouse Efficiency which uses pounds of grain, fermenter volume, and OG.

 

[doug293cz]

That helped a lot, thanks. My hydrometer is calibrated for 60F. That means my pre-boil gravity was 1.039, still way off from 1.057.

I'm reading John Palmer's book, Ch 12 Mash Efficiency. According to the formulas given,

6.75gal pre-boil * 39 points / 12lb grain = 22 points
My grain's potential is 38, so isn't my mash efficiency 22/38 = 58% ?

I'm really getting turned around with the math my first time out here.

I also get your mash efficiency at 58%. But mash efficiency is made up of two terms - how much of the available starch you converted to sugar in the mash (the conversion efficiency), and how much of the sugar created in the mash was collected in your BK (the lauter efficiency.) I got your conversion efficiency at 71% and your lauter efficiency at 81%. Mash efficiency = conversion efficiency * lauter efficiency. Mash efficiency is also the amount of the potential sugar (from starch) in the grain makes it into your BK (the formula you used.) Conversion and mash efficiency are derived from simple measurements, but lauter efficiency is a little more difficult to measure directly, so is usually calculated using lauter efficiency = mash efficiency / conversion efficiency.

Your lauter efficiency is pretty good for a full volume mash, but it's the conversion efficiency which is lower than it could be, and this is easiest to improve by using a finer crush.

Brew on

 

[hotbeer]

If you don't want to go to the expense of getting your own mill and have to rely on what the LHBS or online supplier will mill the grain to, then just be consistent in what you do. Figure out what your efficiency is and then you can fiddle with that in the brewing software you might use to adjust the fermentable amounts accordingly.

With lower efficiency you pretty much just use more malts and other fermentable ingredients. So not really a big deal. It just ups the cost of your six pack or case of beer a little.

You'll make the same OG, FG and other SG predictions with your 58% efficiency as others do better efficiencies if you correct the amounts properly. So don't get too caught up in equating your low efficiency as a failing grade in school. Typically we only grade on what the stuff you pour in our glass tastes like.

All the previous stuff before that glass is just something for us to argue about.

 

[moldmaker]

I'm missing something completely obvious I'm sure; how are you all getting 71%?

 

[doug293cz]

I'm missing something completely obvious I'm sure; how are you all getting 71%?

71% is your estimated conversion efficiency. It's a measure of how much of the starch in the grain you converted to sugar during the mash. Conversion efficiency is always higher than mash efficiency because mash efficiency also includes a measure of how much of the sugar you created got into your BK. The grain always retains some of the wort, which means some of the sugar gets left behind with the spent grain. The fraction of the sugar that was created in the mash that makes it into the BK is defined as the lauter efficiency, and is always less than 1 (whereas conversion efficiency can be 1 [or 100%.])

I estimated your conversion efficiency at 71.4% (or 0.714), and your lauter efficiency as 81.1% (or 0.811).

Mash Efficiency = Conversion Efficiency * Lauter Efficiency (by definition), so your mash efficiency estimate came out as 0.714 * 0.811 = 0.579 (or 57.9%.) This is the same value you got with you simple calculation using points.

The reason for calculating both conversion efficiency and lauter efficiency, is that if your mash efficiency is low, and you want to raise it, you need to know whether you need to improve conversion or lautering. The things needed to improve either of these are different. In your case the place for any desired improvement is in conversion during the mash.

I do my calculations using a rigorous mass balance approach, rather than the simplified points method (the points method is actually pretty accurate.) I also take into account parameters that many other calculators ignore, such as grain moisture content, water consumed by the starch hydrolysis reaction, etc. I have put it all in a spreadsheet, which you can find here. To really use it you need to download a copy into Excel or LibreOffice Calc (free.)

Brew on

 

[moldmaker]

I've been reading and re-reading the last few days. Let me start again. Apologies. I'm really struggling with this.

I mashed 12lb of Maris Otter into 7.5 gal water. I lost .75 gallons to grain absorption. Therefore, 6.75 gallons of wort pre-boil. I got 1.039 for my pre-boil gravity (temp-corrected from 1.020). MO has a potential of 1.038 ppg. Therefore, 38 * 12 / 6.75 = 67 points. 39 actual points / 67 possible points = 58%. This is the conversion efficiency?

The recipe is calling for 1.057 pre-boil and 5 gallons of 1.065 wort into the fermenter. I boiled off 1.5 gallons and ended up with 1.054 and 5.25 gal into the fermenter. 39 / 54 = 72%. Is this brewhouse efficiency?

 

[doug293cz]

I've been reading and re-reading the last few days. Let me start again. Apologies. I'm really struggling with this.

I mashed 12lb of Maris Otter into 7.5 gal water. I lost .75 gallons to grain absorption. Therefore, 6.75 gallons of wort pre-boil. I got 1.039 for my pre-boil gravity (temp-corrected from 1.020). MO has a potential of 1.038 ppg. Therefore, 38 * 12 / 6.75 = 67 points. 39 actual points / 67 possible points = 58%. This is the conversion efficiency?

The recipe is calling for 1.057 pre-boil and 5 gallons of 1.065 wort into the fermenter. I boiled off 1.5 gallons and ended up with 1.054 and 5.25 gal into the fermenter. 39 / 54 = 72%. Is this brewhouse efficiency?

No, what you have calculated is your mash efficiency, which is how much of the max potential sugar from the grain you got into your BK after draining the mash. Conversion efficiency measures how much of the max potential sugar from the grain actually got created (converted from starch to sugar) in the mash. Conversion efficiency does not account for the loss of sugar retained by the wet grain, but mash efficiency does. The loss of sugar in the wet grain is related to the lauter efficiency (lauter efficiency = 1 - fraction of sugar retained by grain.)

Mash efficiency = conversion efficiency * lauter efficiency.

Brew on

 

[balrog]

12 lbs Maris Otter yielding 5.25 gal 1.054 according to the brewers friend brew house efficiency calculator is 62%

 

[doug293cz]

I've been reading and re-reading the last few days. Let me start again. Apologies. I'm really struggling with this.

I mashed 12lb of Maris Otter into 7.5 gal water. I lost .75 gallons to grain absorption. Therefore, 6.75 gallons of wort pre-boil. I got 1.039 for my pre-boil gravity (temp-corrected from 1.020). MO has a potential of 1.038 ppg. Therefore, 38 * 12 / 6.75 = 67 points. 39 actual points / 67 possible points = 58%. This is the conversion efficiency?

The recipe is calling for 1.057 pre-boil and 5 gallons of 1.065 wort into the fermenter. I boiled off 1.5 gallons and ended up with 1.054 and 5.25 gal into the fermenter. 39 / 54 = 72%. Is this brewhouse efficiency?

Sorry, I missed the last paragraph of your post.

The calculation in the last paragraph is not the correct formula for brewhouse efficiency. The correct formula is:

Brewhouse efficiency = Fermenter Volume * 1000 * (OG -1) / Grain Wt * Grain pts/l, or in your case​

​

Brewhouse efficiency = 5.25 * 54 / 12 * 38 = 62.17​

​

But, as we will see next, this value is probably incorrect due to measurement error.

Your pre-boil points were 6.75 * 39 = 263.25, and your fermenter points were 5.25 * 54 = 283.5. This implies you picked up 20+ points during the boil, which is impossible, unless you added some form of sugar during the boil. So, you have volume and/or SG measurement errors going on here.

If all of your measurements are accurate then the following is always true:

Pre-boil volume * (pre-boil SG -1) = post-boil volume * (post-boil SG -1)​

If the above equality does not hold, then one or more of the measurements is erroneous.

Any efficiency value calculated can be no more accurate than the least accurate measurement used in the calculation. (It's the old "garbage in, garbage out.)

Brew on