BIAB gravity much lower than expected

[danomyte]

i just started reading gravity on my brews. my latest gravity reading was way off from what i was hoping (1.052 expected, 1.033 read).

seems like i have a lot more leftover wort (less boil off) than i was planning on. if i use less water next time, will the gravity reading be higher? maybe squeeze the BIAB bag to get more sugar out?

 

[Foosier]

Please provide more information. We need your recipe and mash details like time and temp. Also, was your grain crushed at the LHBS? Single or double crush? Do you adjust your water?

This information is all needed to figure out your issue.

Given that you are new, I would bet that a bad crush is the most likely issue. Most LHBS's crush a bit big so that multi-vessel brewers do not get a stuck sparge. BIAB does not need this and a really fine crush works best. This is usually the first place to start for a newer brewer.

 

[danomyte]

grain was crushed once at LHBS. I'll ask them to run it twice next time! recipe below:

All Grain Recipe - Wheat beer ::: 1.052/1.012 (1 Gal)
Grain Bill (70% Efficiency assumed)
1 lbs. - Wheat Malt
.83 lbs. (13.28 oz) - 2-Row Pale Malt
.167 lbs (2.672 oz)- Caravienne Malt

Hop Schedule
.167 Amarillo 60m
.167 Amarillo 15m
.25 Amarillo 5m
.167 Amarillo 1m
.25 Amarillo dry

2.25 gallons water, strike at 156, Mash at 153° for 60 min.

 

[danomyte]

^ i made that recipe by dividing by 6 from a 6-gallon all grain recipe i found on this site

 

[pricelessbrewing]

How big was the pot you were using? Boiloff is mainly a factor of surface area, how wide the pot is, and how vigorous the boil.

As such, a 1 gallon recipe in a 5 gal pot will have the same boil off rate as a 4gal recipe in the same pot.

What was the final volume? How much water did you use in your strike volume? Squeeze the bag? Any sparge (did you rinse the bag of grain after the mash)?

 

[WayFrae]

Did you cool the wort sample before measuring with your hydrometer? If you took the measurement at mash temps then your 1.033 reading was actually about 1.053.

 

[wilserbrewer]

Wheat kernels are both smaller and harder and than barley, so often this leads to a poor crush. The best defense IME is to examine the grain to ascertain if all, or at least the vast majority of kernels are fractured.
http://thebrewingnetwork.com/forum/viewtopic.php?f=2&t=21623

Yes, creating too much wort will also lower your gravity.

Fixing these two issues will likely help tremendously. Cheers!

 

[peterj]

I don't think it's necessarily an issue with the crush. If you ended up with more wort than you were expecting, then that is probably the issue. More wort means you have the same amount of sugar but more water. Which means it's too diluted so your OG will be too low. What was your post boil volume?

 

[danomyte]

i'm using a 3 gallon pot and ended up with what i would guess was 1 and a quarter to 1 and a half gallons of final volume. i should have measured, but i filled the 1 gallon fermentor and dumped the rest. strike volume was 2.25 gal. no squeeze, no sparge.

when converting an all grain recipe to BIAB, should i be sparging?

 

[danomyte]

Did you cool the wort sample before measuring with your hydrometer? If you took the measurement at mash temps then your 1.033 reading was actually about 1.053.

i didn't cool it but ran the numbers through a calculator http://www.brewersfriend.com/hydrometer-temp/
to get 1.033

 

[wilserbrewer]

I don't think it's necessarily an issue with the crush. If you ended up with more wort than you were expecting, then that is probably the issue.

(1.052 expected, 1.033 read)

Unless he had an additional boat load of wort, that is a significant gravity delta...to be caused by overshooting volume... just a hunch.

 

[danomyte]

I don't think it's necessarily an issue with the crush. If you ended up with more wort than you were expecting, then that is probably the issue. More wort means you have the same amount of sugar but more water. Which means it's too diluted so your OG will be too low. What was your post boil volume?

this is what i think is most likely happening. ended up with 1.25 -1.5 gal post boil volume. didn't measure it but i dumped a bunch after filling the fermentor

 

[WayFrae]

i'm using a 3 gallon pot and ended up with what i would guess was 1 and a quarter to 1 and a half gallons of final volume. i should have measured, but i filled the 1 gallon fermentor and dumped the rest. strike volume was 2.25 gal. no squeeze, no sparge.

when converting an all grain recipe to BIAB, should i be sparging?

I do no sparge BIAB and I consistently get 75% efficiency. I squeeze the **** out of my bag though. Try measuring your exact boil off rate. Knowing your boil off rate will help you hit your final volume with ease.

 

[wilserbrewer]

this is what i think is most likely happening. ended up with 1.25 -1.5 gal post boil volume.

Well I humbly stand corrected ...if you generated 50% too much wort, your gravity would be reduced by a third. Or .052 * .66 = .034 of 1.034 there ya go!

That is the tricky issue with small batch brewing, volumes become very critical because they are a large percentage of batch size.

 

[peterj]

i'm using a 3 gallon pot and ended up with what i would guess was 1 and a quarter to 1 and a half gallons of final volume. i should have measured, but i filled the 1 gallon fermentor and dumped the rest. strike volume was 2.25 gal. no squeeze, no sparge.

when converting an all grain recipe to BIAB, should i be sparging?

That's your problem. Assuming it was about 1.5 gallons, if you would have boiled down to 1 gallon (or used less water to begin with) you would have been right around your desired OG. Especially with 1 gallon batches it is very important to hit your post boil volume right on. When you tossed the "extra" wort you were throwing out sugars that should have been in your wort.

You need to calculate your boil off rate and then adjust your water additions so that you will end up with 1 gallon after the boil.

 

[danomyte]

I do no sparge BIAB and I consistently get 75% efficiency. I squeeze the **** out of my bag though. Try measuring your exact boil off rate. Knowing your boil off rate will help you hit your final volume with ease.

will definitely start measuring that. cheers!

 

[danomyte]

Well I humbly stand corrected...if you generated 50% too much wort, your gravity woud be reduced by a third.

totally makes sense. i'll start with less water next time

 

[danomyte]

That's your problem. Assuming it was about 1.5 gallons, if you would have boiled down to 1 gallon (or used less water to begin with) you would have been right around your desired OG. Especially with 1 gallon batches it is very important to hit your post boil volume right on. When you tossed the "extra" wort you were throwing out sugars that should have been in your wort.

You need to calculate your boil off rate and then adjust your water additions so that you will end up with 1 gallon after the boil.

thanks so much for the info. this helps a lot!

 

[RM-MN]

Wheat is difficult to get good efficiency on because the kernels are smaller and harder so it needs to be crushed with a smaller opening on the mill. Over half your fermentables should have come from the wheat malt so if you didn't get a really good crush.......

 

[danomyte]

i got a hilariously high amount of water to use by using this:
http://biabcalculator.com/

it said to start with 2.6 gallons. i went with 2.25 but will start with 2 next time.

is that calculator broke? or am i not using it right?

 

[peterj]

i got a hilariously high amount of water to use by using this:
http://biabcalculator.com/

it said to start with 2.6 gallons. i went with 2.25 but will start with 2 next time.

is that calculator broke? or am i not using it right?

It looks like it has an input for boil off rate that is automatically set to 1.25 gallons/hour. I sounds like you got about 0.5 gallon/hour. So just adjust that field in the calculator to suit your setup and you should be good.

You don't really even need the calculator. Absorption is around 0.5 qt per pound of grain so 2 lbs will absorb about 1 quart of water. Then you want 1.5 gallons at the start of your boil so you can boil off 0.5 gallon to end up at 1 gallon. So you should start with 1.75 gallons of total water.

 

[pricelessbrewing]

I double checked the calculator. I guessed boil off around .5 and .1 loss to trub. Recommends 1.7 gal strike full volume mash. You really do need to measure your boil off if you want accuracy at all.

 

[wilserbrewer]

With such small batches where volume is so critical, I would suggest having your kettle marked, or having a dip stick to determine post boil volume. If your are over volume say prior to your last hop addition, extend the boil, but time the late hops to the anticipated end of the boil. Basically, try and pay attention to where you are going, rather than be surprised when you end up 50% over. This really applies to any size batch brewing, but just that it is more critical with smaller batches.

 

[danomyte]

thanks all for your help and advice. will be measuring boil off for sure in the future!