post boil gravity

[matc]

I'm having a hard time nailing my post boil gravity using beersmith. Do you guys have any idea ?

On my last few batches, the pre-boil gravity was always within 2 points of what beersmith predicted but for the post boil gravity, I often get 8 points lower than expected. I use an hydrometer that shows 1.0 in water so it can't be the problem.

I brew indoor with 2 elements that are always fully powered. My evaporation rate on beersmith seems ok with what I get and my volumes are spot on too. I'm lost...I start my 60 min boils as soon as I see big buggles breaking the foam on top.

Today's batch, an ipa, I nailed my pre-boil gravity and volume. After the 60 minutes boil, I was down to 16 L (beersmith said 17L) and my gravity was 1.058 instead of 1.068. I'm lost...I boiled 1 liter more than predicted but I'm still short of 10 points !!!


edit : If I boiled the wort for longer, my volumes would not match so I'm not sure how to fix this with beersmith

 

[Derek1985]

I'm having a hard time nailing my post boil gravity using beersmith. Do you guys have any idea ?

On my last few batches, the pre-boil gravity was always within 2 points of what beersmith predicted but for the post boil gravity, I often get 8 points lower than expected. I use an hydrometer that shows 1.0 in water so it can't be the problem.

I brew indoor with 2 elements that are always fully powered. My evaporation rate on beersmith seems ok with what I get and my volumes are spot on too. I'm lost...I start my 60 min boils as soon as I see big buggles breaking the foam on top.

Today's batch, an ipa, I nailed my pre-boil gravity and volume. After the 60 minutes boil, I was down to 16 L (beersmith said 17L) and my gravity was 1.058 instead of 1.068. I'm lost...I boiled 1 liter more than predicted but I'm still short of 10 points !!!


edit : If I boiled the wort for longer, my volumes would not match so I'm not sure how to fix this with beersmith

Adjust your target Pre boil volume. your obviously boiling off more than expected so just compensate up front. You may need to tweak some other parameters of your recipe but your Post boil gravity should be in line.

EDIT: I misread your post. That is odd. you boiled off more and still were short. Are you cooling your hydrometer samples?

 

[matc]

yep I am cooling them...The only thing I can think about is that I made a mistake on my pre boil gravity but this is unlikely as I check 2-3 times to be sure

 

[Derek1985]

I use an hydrometer that shows 1.0 in water so it can't be the problem.

So your hydrometer is calibrated and you cool your samples. Scratch that.

My evaporation rate on beersmith seems ok with what I get and my volumes are spot on too. I'm lost...I start my 60 min boils as soon as I see big buggles breaking the foam on top.

What is your rate? Do you have the volumes (pre and post) from your last batch as reference? How long does it takes to get to your big bubbles?

I nailed my pre-boil gravity.....After the 60 minutes boil, I was down to 16 L (beersmith said 17L) and my gravity was 1.058 instead of 1.068.

What is your kettle size and geometry? Are you boiling off less than you think? What temperature do you cool your SG samples to?

Let's take a problem solving approach:

1.) Forget BeerSmith for a minute
2.) Pre-boil Gravity is what it is and you say your hitting yours. The only delta here would be you misreading your hydrometer. Taking your word as gospel here so that is out.
3.) Pre-boil volume is on point. Again, nothing to see here.
4.) You are boiling off more wort than predicted and missing OG. This is suspect. Again, the only red flag here at this point is either a mistake in reading the hydrometer or a mistake in measuring your volume Post-boil.
5.) If you are taking accurate readings with 60 deg. F wort and accurately measuring your volumes then you should be close OG wise.

 

[doug293cz]

(Pre-Boil_SG - 1) * Pre-Boil_Volume must = (Post-Boil_SG - 1) * Post-Boil_Volume

If it doesn't, then one or more of your volume or SG measurements is wrong, or you spilled a lot of wort. The amount of sugar in your BK is constant. Boiling does not evaporate any sugar. (SG - 1) * Volume is proportional to sugar weight, so if sugar weight is constant, then (SG - 1) * Volume also has to be constant.

What are your pre-boil SG, pre-boil volume, post-boil SG, and post boil volume? The last two have to both be measured before top off water, or both be measured after top off water. If one is before and one after, then you will get invalid results.

Brew on

 

[Derek1985]

(Pre-Boil_SG - 1) * Pre-Boil_Volume must = (Post-Boil_SG - 1) * Post-Boil_Volume

If it doesn't, then one or more of your volume or SG measurements is wrong, or you spilled a lot of wort. The amount of sugar in your BK is constant. Boiling does not evaporate any sugar. (SG - 1) * Volume is proportional to sugar weight, so if sugar weight is constant, then (SG - 1) * Volume also has to be constant.

What are your pre-boil SG, pre-boil volume, post-boil SG, and post boil volume? The last two have to both be measured before top off water, or both be measured after top off water. If one is before and one after, then you will get invalid results.

Brew on

Buy this man a beer, he may have just cracked the case.

 

[MagicMatt]

How are you measuring your volumes? Hopefully you've created your own calibrated method and are not going by the (very likely incorrect) markings on your kettle or fermenter?

 

[matc]

pre boil sg was 1.051 (temp was 46 but I corrected it with a chart)
pre boil volume was 21 L, using my sight glass on my keggle. The sight glass was painfully calibrated using a water bucket and balance, 1 liter at a time.

Post boil volume was 16 L
post boil sg was 1.058.

I think I will begin by doing some tests on my keggle to make sure the sight glass is right.

 

[matc]

(Pre-Boil_SG - 1) * Pre-Boil_Volume must = (Post-Boil_SG - 1) * Post-Boil_Volume

If it doesn't, then one or more of your volume or SG measurements is wrong, or you spilled a lot of wort. The amount of sugar in your BK is constant. Boiling does not evaporate any sugar. (SG - 1) * Volume is proportional to sugar weight, so if sugar weight is constant, then (SG - 1) * Volume also has to be constant.

What are your pre-boil SG, pre-boil volume, post-boil SG, and post boil volume? The last two have to both be measured before top off water, or both be measured after top off water. If one is before and one after, then you will get invalid results.

Brew on

ok are my numbers right in your equation ?

(Pre-Boil_SG - 1) * Pre-Boil_Volume must = (Post-Boil_SG - 1) * Post-Boil_Volume

pre boil : (1.051-1) * 21 = 1.071
post boil : (1.058-1)*16 = 0.928

Obviously either my volumes or gravities are wrong ?

 

[doug293cz]

ok are my numbers right in your equation ?

(Pre-Boil_SG - 1) * Pre-Boil_Volume must = (Post-Boil_SG - 1) * Post-Boil_Volume

pre boil 1.051-1) * 21 = 1.071
post boil : (1.058-1)*16 = 0.928

Obviously either my volumes or gravities are wrong ?

One or more has to be wrong (unless you spilled a lot of wort.)

Brew on

 

[matc]

another question though....I ran the predicted beersmith numbers and came up with this..it seems impossible to get such a high OG with the pre boil gravity

predicted pre boil volume = 21 L,
predicted pre boil gravity = 1.052

(1.052-1)*21 = 1.092

predicted post boil volume = 17 L
predicted post boil gravity = 1.068

(1.068-1)*17 = 1.156

156-92 = 64 of difference. Maybe beersmith is totally wrong ???

 

[Derek1985]

It's either you sight glass is wrong or you hydrometer readings are wrong.

Was 1.051 your corrected SG?

I agree that it is a physical impossibility to boil off 1.25 gallons of wort and only get 7 gravity points. I'd be more inclined to say it's the sight glass.

 

[Derek1985]

another question though....I ran the predicted beersmith numbers and came up with this..it seems impossible to get such a high OG with the pre boil gravity

predicted pre boil volume = 21 L,
predicted pre boil gravity = 1.052

(1.052-1)*21 = 1.092

predicted post boil volume = 17 L
predicted post boil gravity = 1.068

(1.068-1)*17 = 1.156

156-92 = 64 of difference. Maybe beersmith is totally wrong ???

Your using liters. You need to use gallons with specific gravity.

 

[Derek1985]

ok are my numbers right in your equation ?

(Pre-Boil_SG - 1) * Pre-Boil_Volume must = (Post-Boil_SG - 1) * Post-Boil_Volume

pre boil : (1.051-1) * 21 = 1.071
post boil : (1.058-1)*16 = 0.928

Obviously either my volumes or gravities are wrong ?

It's:

(PBG*pre boil volume)/post boil volume = OG

(51*5.25)/4 = ~67 --> (67/1000)+1 = 1.067

 

[MagicMatt]

Maybe beersmith is totally wrong ???

Unlikely. I bet both your sight glass and hydrometer are to cause for the discrepancy.

You say you measured your wort sample at 46°C (114°F) - that's way too hot! Yes, there are charts to adjust for temp differences between the sample and what the hydrometer was calibrated to, but they are only meant for relatively minor adjustments - up to say 20°F from calibration temp. That would mean you shouldn't be testing until the temp cools below ~80°-90°F (26°-32°C) minimum. Also, Beersmith has this tool built in ("Hydrometer Adjust").

Regarding the sight glass, I bet when you calibrated it you used room temp water? Hot wort will occupy a significantly larger volume than water at ambient temps. You can easily test this by adding a given amount of water (measured using the sight glass and at room temp), cover and heat it to near boiling. I bet the volume increases enough to throw off your readings.

I used my mash paddle to mark my volumes, and I have a different scale on 3 of the 4 sides. One scale for measuring room temp water (which will be heated for strike), one is calibrated for 165°F wort (for measuring lauter collection), and the last is calibrated to boiling volumes, for determining when I've hit my desired volume.

 

[55x11]

It's either you sight glass is wrong or you hydrometer readings are wrong.

Was 1.051 your corrected SG?

I agree that it is a physical impossibility to boil off 1.25 gallons of wort and only get 7 gravity points. I'd be more inclined to say it's the sight glass.

Are you sure the pre-boil wort is well mixed up and you are not measuring some early runnings that are higher SG, as opposed to the average value for entire wort.

In other words, is your wort homogeneous and sample representative of that?

 

[doug293cz]

another question though....I ran the predicted beersmith numbers and came up with this..it seems impossible to get such a high OG with the pre boil gravity

predicted pre boil volume = 21 L,
predicted pre boil gravity = 1.052

(1.052-1)*21 = 1.092

predicted post boil volume = 17 L
predicted post boil gravity = 1.068

(1.068-1)*17 = 1.156

156-92 = 64 of difference. Maybe beersmith is totally wrong ???

When I set Beersmith up for a 21 L (5.55 gal) pre-boil volume, 1.052 pre-boil SG, and 17 L (4.49 gal) post-boil volume, it predicts a post-boil SG of 1.064 (not 1.068)

21 * 0.052 = 1.092
17 * 0.064 = 1.088​

That error is within rounding error due to using only 3 digits for SG.

Brew on

 

[doug293cz]

Your using liters. You need to use gallons with specific gravity.

No you don't.

21 L * 0.264172 gal/L * pre-boil_SG = 17 L * 0.264172 gal/L * post-boil_SG

reduces to:​

21 L * pre-boil_SG = 17 L * post-boil_SG
​

It's basic algebra. The resulting units are different, but so what? You only have to work in gallons and pounds if you want to work with ppg. The basic sugar mass balance equation is valid no matter what units you use.

Brew on

 

[Derek1985]

Mathematics aside, something isn't right.

 

[doug293cz]

21 * 0.052 = 1.092
17 * 0.064 = 1.088​

/QUOTE]

Again, these shouldn't be taken separately. They are part of an equality:

PBG*preV=OG*postV

Also, gallons should be used with SG.

So:

(52*5.5)/4.2=68=1.068

Appears you can't even convert from liters to gallons correctly.

21 L * 0.264172 gal/L = 5.547612
17 L * 0.264172 gal/L = 4.490924​

so that

1000 * (1.052 - 1) * 5.547612 / 4.490924 = 64.235
64.235 points/gal => 1.064235 SG, which rounds to 1.064​

Same numbers you get if you do the math in liters.

52 * 21 / 17 = 64.235​

Back to 8th grade for you.

Brew on

 

[Derek1985]

Relax. His post boil volume was 16L.

21*.052/16=~1.068

 

[Derek1985]

Appears you can't even convert from liters to gallons correctly.

21 L * 0.264172 gal/L = 5.547612
17 L * 0.264172 gal/L = 4.490924​

so that

1000 * (1.052 - 1) * 5.547612 / 4.490924 = 64.235
64.235 points/gal => 1.064235 SG, which rounds to 1.064​

Same numbers you get if you do the math in liters.

52 * 21 / 17 = 64.235​

Back to 8th grade for you.

Brew on

I think I'm most offended by the goat. I always thought myself more of an Ox

 

[doug293cz]

I think I'm most offended by the goat. I always thought myself more of an Ox

I don't think we have an ox emoticon available to us.

Brew on

 

[Derek1985]

I don't think we have an ox emoticon available to us.

Brew on

And apology accepted for the digs against algebra skills.

 

[doug293cz]

Relax. His post boil volume was 16L.

21*.052/16=~1.068

I used 17 because I was responding to the following post where the OP was questioning the Beersmith predictions. Therefore, I used the predicted numbers.

another question though....I ran the predicted beersmith numbers and came up with this..it seems impossible to get such a high OG with the pre boil gravity

predicted pre boil volume = 21 L,
predicted pre boil gravity = 1.052

(1.052-1)*21 = 1.092

predicted post boil volume = 17 L
predicted post boil gravity = 1.068

(1.068-1)*17 = 1.156

156-92 = 64 of difference. Maybe beersmith is totally wrong ???

I agree that if his post-boil was 16 L and the pre-boil measurements were correct, then he should have had:

1000 * (1.051 - 1) * 21 / 16 = 67. (In one of his posts he said his actual pre-boil was 0.051.

For the numbers to work, you have to use all actual or all predicted. Mixing them will get you confused.

Brew on

 

[Derek1985]

Agreed.

Cheers man.

 

[matc]

Someone assumed I measured my gravity at 46 C but I use Fahrenheit when brewing, so my sample was taken at 46F, which is cold and needs to be corrected slightly.

So with all that said Doug, I guess I should recheck my hydrometer reading with water at room temp and triple check my sight glass using boiling water ? When I calibrated it, I used tap water at like 70F I guess.

 

[Derek1985]

So was your corrected SG 1.051? Or your 46F reading was 1.051

 

[matc]

all my gravity readings are corrected to 60F

 

[chickypad]

Are you sure the pre-boil wort is well mixed up and you are not measuring some early runnings that are higher SG, as opposed to the average value for entire wort.

In other words, is your wort homogeneous and sample representative of that?

OP, didn't see if you addressed this yet. IME this is a cause of discrepancy when the volumes are accurate.