Why did I lose gravity during my boil

[Ylbc]

Hey guys,

Long time lurker first time posting, love the forum and all the info you guys have.

So yesterday I brewed an all grain IPA using BIAB and doing a five gallon batch. Everything was going well. Used Beersmith to calculate my day. Hit my post mash gravity of 1.059 with 7.5 gallons of wort. After my boil I had 6.15 gal after cooling, where beersmith expected 6.25. Assuming 4% shrinkage to cooling I estimate my post boil size at 6.4 gallons so slightly more than what beersmith expected. However my post boil gravity was 1.063 where beersmith expected 1.073.

My grain bill was

12 lb of 2 row
2 lb of flaked oats
12 oz Munich malt

I took the gravity reading after a whirlpool hop and using my immersion chiller.

Any idea what could have happened?

 

[Qhrumphf]

Presumably your preboil reading was wrong, although that's less likely to be the case with BIAB than with traditional multi vessel sparging methods.

Assuming temps corrected, there's no way for your gravities to line up with the volumes you've listed, therefore one of them has to be wrong (gravity or volume).

G1*V1=G2*V2 with gravity expressed as points (ie 59 instead of 1.059).

 

[day_trippr]

fwiw, with that grain bill my math says the 7.5 gallon SG should be 1.054, at 6.25 it should be 1.065, and at 6.4 it should be 1.063...

Maybe a data entry error in BS2?

Cheers!

 

[Ylbc]

Thanks guys. Let me double check my beer Smith entries. Thanks again.

 

[GrimBrewer]

Did you adjust your first gravity reading with the temperature of the wort?

 

[Ylbc]

@grimbrewer yea I did. I actually let it sit for a long time and took the reading at 70 degrees and adjusted it for temp. I did this for both of the readings. The post mash one sat for an extended period of time actually. The reading adjusted for temp and at 70 degrees both came out the same.

 

[Morrey]

What was your full volume (strike) you started with? After you pull out your grain bag and squeeze, you will have some amount of absorption or loss at that point. Unless you are hitting some higher than normal numbers there, you'll likely lose .75 gallons of water due to absorption with that grain bill. This needs to be accounted for as a loss. Normal evap in my system is 1.25G for an hour boil.

You can set efficiency after you get some numbers under your belt, but I think 72% is the default number.

I check my SG before I start the 60 min boil, and as a rule of thumb, I'll increase my SG by 8 or 9 points due to evap losses and concentration of the wort after the boil is done.

 

[kh54s10]

I suspect that for some reason one of your numbers is wrong. It could be any of the gravity readings or volume readings.

Looking at this calculator: https://www.brewersfriend.com/dilution-and-boiloff-gravity-calculator/

It says if you started with 1.059 and 7.5 gallons, then ended up with 6.15 gallons your OG should have been close to 1.080.

 

[Morrey]

I suspect that for some reason one of your numbers is wrong. It could be any of the gravity readings or volume readings.

Looking at this calculator: https://www.brewersfriend.com/dilution-and-boiloff-gravity-calculator/

It says if you started with 1.059 and 7.5 gallons, then ended up with 6.15 gallons your OG should have been close to 1.080.

My guess too. Volumes are often the culprit when numbers are skewed like this. Not saying SG readings are to overlooked either as small errors make big differences.

 

[Ylbc]

Thanks guys. I'm going to chalk this up as an issue with my volume measurements. I was using the etched lines on my pot but it might be time to move up to something more accurate. How are you guys measuring volumes?

 

[Morrey]

Thanks guys. I'm going to chalk this up as an issue with my volume measurements. I was using the etched lines on my pot but it might be time to move up to something more accurate. How are you guys measuring volumes?

I have a kettle with a sight glass but the markings inside your kettle are often the best of all. Some folks that have neither of these options may use some type of measuring stick with marks on it representing volumes.

It is a learning experience for us all and nobody is accurate all the time. Once you get some practice with SG and volumes, you'll sort of know what to expect and can react if you see something wrong. This can help you to adjust your OG by boiling longer or adding water. Some keep DME handy in case of an on the fly adjustment. All good!!

 

[doug293cz]

Thanks guys. I'm going to chalk this up as an issue with my volume measurements. I was using the etched lines on my pot but it might be time to move up to something more accurate. How are you guys measuring volumes?

You might want to check the accuracy of the etched lines in your kettle (if you haven't already.) Add measured amounts of water to the kettle, and compare to the markings.

Brew on

 

[Qhrumphf]

You might want to check the accuracy of the etched lines in your kettle (if you haven't already.) Add measured amounts of water to the kettle, and compare to the markings.

Brew on

This.

On both my 10 gallon home kettle and 16 bbl work kettle, volume markers are hand marked and self-calibrated initially and then mathematically continued once safe to do so (measured volumes and etched in the former, flow meter and marked sight glass in the latter, and then math for cylinder volume beyond that after various hardware is no longer a factor), and both are dead on. I'd suspect any factory markings as being inaccurate, and particularly any self made ones if you weren't diligent marking them.

Both are absolutely spot on.

I'd double check the calibration of your etchings.

 

[Chanoc]

@grimbrewer yea I did. I actually let it sit for a long time and took the reading at 70 degrees and adjusted it for temp. I did this for both of the readings. The post mash one sat for an extended period of time actually. The reading adjusted for temp and at 70 degrees both came out the same.

If vessel mouth size was wide, enough evaporation must have taken place to alter reading towards higher gravity.
When I cool samples for hydro readings, I cover vessel or flask with cling film.
HTH.

 

[Dog House Brew]

Thanks guys. I'm going to chalk this up as an issue with my volume measurements. I was using the etched lines on my pot but it might be time to move up to something more accurate. How are you guys measuring volumes?

I'm very scientific, wooden dowel with marked rings.

 

[frozyn]

Thanks guys. I'm going to chalk this up as an issue with my volume measurements. I was using the etched lines on my pot but it might be time to move up to something more accurate. How are you guys measuring volumes?

Ruler and an Excel spreadsheet that can tell me the amount of liquid based on the height on the ruler. With pre- and post-boil readings, I also take a temperature reading and adjust using http://www.engineeringtoolbox.com/volumetric-temperature-expansion-d_315.html to account for thermal expansion. Adding the formula to my worksheet is on my list of things to do.

EDIT: Adding that the website linked above doesn't account for the sugars left behind in the water post-mash, but that's not something I'm worried about......yet.

 

[smyrnaquince]

Another possibility is that you did not stir sufficiently before taking your samples, so your readings were off.

 

[balrog]

I measured and etched markings in my kettle very VERY carefully and then realized that I almost *NEVER* have the danged kettle perfectly level, making any reading suspect, when on the burner, on the garage floor, on the table in the garage.

Just sayin.

 

[GrimBrewer]

Small batches I just meassure the wort wth a measuring jug. For big boils we use my dads old 55liter grayfish pot, it has a lots of dents. Bottoms not flat, so measuring the wort volume is a issue. In the begining we use to count the wort as we sparged into a jug. But since we now know our system volumes a lot better, we dont botter using a measuring jug untill it gets into the fermenter. Where we do have accurate markings.

I do keep dme as backup.

 

[RichBenn]

I recently was WAY off on a BIAB brew. My water is well water, extremely soft, and I use a spreadsheet for what to add to the water for different beer. After many brews with spot on values, I stopped measuring pH.

Wrong! Got way low extraction, so I tested mash H and it was over 6.0. Apparently the record setting snows this year have changed my water. So mash pH is one possibility for you, although that may mot explain all of it.

The second possibility is the grind. Before I started grinding my own grain, I could see variances like you are seeing. Did you change vendors on pre-crushed grain?

Hope you figure it out. Dialing in your system is nice, as you can get more consistent results. Adding some DME or less bittering hops are a couple of ways to correct when you have these problems.