Hit pre-boil gravity but OG too low

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happypanties

happypanties

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I continue to have a problem with my BIAB process where my OG is coming out too low. I have been formulating my recipes with BeerSmith, and trying to hit my numbers. Last brew I hit my pre-boil gravity of 1.032 and missed my target OG by 8 points, got 1.044 when I BeerSmjth estimates 1.052.

This seems to continually be a problem for me. Only thing I can think of is my boil-off rate might not be set right or something. Any ideas why my OG keeps coming out low?
 
doing BIAB I assume you are doing full boil mashing and not adding top off water. Not sure, what temp are you taking OG? I'm never more than a point or two off.
 
Can you just keep boiling until you would hit your gravity? I hate doing it because less than 5 gallons go's into the fermentor and then I have less brew at the end. But if tour consistent in being low, maybe n additional half hour in your boil may be necessary.

What's your boil off rate? Volume of pre boil? Hows the crush? Are you adjusting your gravity readings for temperature? 1.044 reading at 105* corrects to 1.052.
 
C-Rider said:
doing BIAB I assume you are doing full boil mashing and not adding top off water. Not sure, what temp are you taking OG? I'm never more than a point or two off.
Click to expand...

Yes full boil (2.5 gal batch). Took OG with Hydrometer at 72 degrees and compensated for temp using scale, also used refractometer to verify. Both came out at 1.032 pre-boil and 1.044 OG
 
TangoHotel said:
Can you just keep boiling until you would hit your gravity? I hate doing it because less than 5 gallons go's into the fermentor and then I have less brew at the end. But if tour consistent in being low, maybe n additional half hour in your boil may be necessary.

What's your boil off rate? Volume of pre boil? Hows the crush? Are you adjusting your gravity readings for temperature? 1.044 reading at 105* corrects to 1.052.
Click to expand...

I was thinking I could continue the boil to raise the OG but I had completed my hop schedule already and thought that would make the beer too bitter and lose hop flavor/aroma.

I have tested my boil off rate in the past and came out to 1.15 gal/hr. I've programmed this into BeerSmith. The day of brewing it was a bit humid and we had all the windows open, I wonder if that had something to do with it?

Yes I am adjusting gravity readings for temp (see previous post).
 
What was your pre-boil gravity and volume? What did you expect them to be?

What was your post-boil gravity and volume? What did you expect them to be?

Assuming that the calculations were done correctly, if you had the expected pre-boil gravity, expected pre-boil volume, and expected post-boil volume, then it should be impossible to not have your expected post-boil gravity.

By the way, if your pre-boil gravity and volume are correct, you are past the point where BIAB or 3V makes a difference.
 
happypanties said:
...... Last brew I hit my pre-boil gravity of 1.032 and missed my target OG by 8 points, got 1.044 when I BeerSmjth estimates 1.052.....
Click to expand...

Seems to me there is a software glitch or something incorrect in the settings.

BeerSmith is telling you the pre-boil gravity should be 1.032 and the post-boil should be 1.052?

That is a pretty big swing - that's a gravity increase of 63% during the course of the boil. That can't be right....unless you just boil off a ton of water, I can't see how the graivity could jump up that much.
 
smyrnaquince said:
if you had the expected pre-boil gravity, expected pre-boil volume, and expected post-boil volume, then it should be impossible to not have your expected post-boil gravity.
Click to expand...

I was going to post this. You didn't mention if you were hitting your anticipated pre and post boil volumes. The boiloff rate that is set as the default in Beersmith is rather high, but you're supposed to enter your own rate. On a kitchen stove with a (7 gallon) boil I usually see about 0.5-0.6 gallons per hour. Gravity points don't just disappear; if you're hitting your preboil volume and gravity, but your postboil gravity is too low, it just means you have a higher postboil volume than you anticipated. Measure the volume change over the next few batches and input that into beersmith. If you aren't measuring all your volumes, you should. Volume measurements are just as important as gravity measurements.
 
DustBow said:
BeerSmith is telling you the pre-boil gravity should be 1.032 and the post-boil should be 1.052?

That is a pretty big swing - that's a gravity increase of 63% during the course of the boil. That can't be right....unless you just boil off a ton of water, I can't see how the graivity could jump up that much.
Click to expand...

This! Unless perhaps you are boiling 4 gallons down to 2.5. This will be a little trickier w/ small batch brewing where you are boiling off a large percentage of the original volume!

Next time take a pre boil gravity and determine final volume with the simple ratio...

(pre boil og / post boil og) X preboil vol. = post boil vol

and boil to that post boil volume to get your post boil gravity....

Would someone kindly check my logic here...I think I got it right?

Software like beersmith is great...but simple checks the old fashioned way are still valuable IMHO.
 
Replying to this old thread just because I have ran into this a couple times and have a couple of observations to throw out on the table in case anybody else finds this thread, I have only experienced this with higher OG brews, 1.075 and higher.

Here are the steps I've taken and observed:
1. Took preboil OG readings and hit where I should have, correct amount of wort and OG was where it should have been based on my efficiency.
2. Boil off calculation was right and ended the boil with the correct amount of wort, pull a sample and throw it in the freezer while cooling the wort down.
3. Once wort is cooled to pitching temp, pull another sample
4. Measure both samples and OG has been 5-10 points lower than it should have been
5. Pitch yeast and rack brain over why the OG ended up low
6. Take reading the next morning, roughly 12 hours after pitching, yes i realize all depending on how quick the yeast kicks in this might not be an option
7. OG reading is within a point or two of where it should have been
 
bolus14 said:
Replying to this old thread just because I have ran into this a couple times and have a couple of observations to throw out on the table in case anybody else finds this thread, I have only experienced this with higher OG brews, 1.075 and higher.

Here are the steps I've taken and observed:
1. Took preboil OG readings and hit where I should have, correct amount of wort and OG was where it should have been based on my efficiency.
2. Boil off calculation was right and ended the boil with the correct amount of wort, pull a sample and throw it in the freezer while cooling the wort down.
3. Once wort is cooled to pitching temp, pull another sample
4. Measure both samples and OG has been 5-10 points lower than it should have been
5. Pitch yeast and rack brain over why the OG ended up low
6. Take reading the next morning, roughly 12 hours after pitching, yes i realize all depending on how quick the yeast kicks in this might not be an option
7. OG reading is within a point or two of where it should have been
Click to expand...

This has happened to me several times and I'm still wondering why . Last Sunday, in fact, I hit all of my numbers perfectly up until the OG. Volumes and specific gravities were spot on otherwise. I didn't take a reading the next day but that's an interesting bit.

I figured maybe I mis-measured my preboil gravity but this has happened several times so I don't know. I also am curious about my hydrometer. I've heard that as SG increases, it becomes less accurate at measuring sugar content. Brix is supposed to be more accurate so could that be it? Are the numbers skewing? I'm lost.
 
Here's an idea: could the concentrated amount of non-sugar particulate matter in the post boil wort be skewing the numbers? Especially in a bigger beer, it might make sense that there's extra stuff in there that a lighter beer may not have. If you get an accurate reading the following day, maybe that's because the extra grain and hop particles have a chance to settle out some.
 

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