gravity goes backwards in the boil?

[philipCT]

Never seen this before...

Pre-boil target gravity: 1.044
Pre-boil actual gravity: 1.048

Close enough, right? And in any case, seems like the result of good conversion. Temps and pH's of mash were all good, so this makes sense.

Boil for 60 minutes.

Post-boil target gravity (O.G.): 1.055
Post-boil actual gravity (O.G.): 1.045

Huh? I didn't know gravity could go "backwards".

I triple checked both sets of readings too. With separate samples. And the O.G. was so outrageously weird, I checked it a fourth time with the hydrometer.

I've never brewed with wheat before, so I don't know if that has anything to do with it. My last four brew sessions have behaved perfectly in terms of expected pH and gravities so this is really weird.

Anyone ever seen anything like this before?

 

[tootal]

Were both samples taken at 60 or 68 degrees? (Whatever you hydrometer is calculated at).

 

[philipCT]

Were both samples taken at 60 or 68 degrees? (Whatever you hydrometer is calculated at).

I use a refractometer almost exclusively on brewday. I have a standard routine for cooling small wort samples by swirling in a small aluminum bowl sitting in chilled water. It takes about 1 minite. The first samples were taken at 69F. The second samples were also at 69F.

 

[plumbrew]

Did you stir the wort in your kettle before taking the sample both Pre and Post Boil? Gravity readings can be wildly different between not stirred and stirred.

 

[philipCT]

Yes. I make sure to stir pretty well, and mix the lower strata of wort upward to counter vertical stratification.

Even the first reading was strange to me, so I went back and stirred some more, and then resampled, and took a new measurement. I took 4 separate readings and got:

Brix - S.G. Equiv
11.2 - 1.045
10.0 - 1.040
12.1 - 1.049 and finally
12.0 - 1.048
​

I wasn't comfortable with those readings coming in so far apart, so since the last two were from a second-stirred separate sample and they agreed, that's the one I went with.

Even if the pre-boil SG was 1.040, I would expect to 10-15 points during the boil. The whole thing is weird.

 

[edroberts]

Any chance you had some heavy scorching of the wort in the boil kettle? Skimming off the foam during the hot break can take away some sugars as well. I still wouldn't expect either to overcome an hour of evaporation, but there are some potential sugar losses.
Also, I'd check the calibration on your refractometer. This can sometimes play havoc with readings.

 

[philipCT]

I didn't detect any scorching and have never had an issue with this, so I don't suspect that.

I didn't scoop the foop (hot break), so I guess that probably fell back in.

I did read this post elsewhere in this forum.

Although very informative, and I'd like an easy answer, I don't think this is my issue for this reason: I took two samples for the post-boil readings. The first was a pipette extraction directly from the kettle (stupid thing to do - risks infection - I don't usually do that) and then cooled. The second was from a little spillage that came out of the chiller when I was switching hoses (don't ask). Both readings agreed at 11.2 Brix/1.045. I then used the post-chiller wort (at 65F) in my hydrometer and got the same.

According to the post above, the post-chiller sample could have been missing a few points due to cold-break, but then I would expect the kettle-direct sample would not have agreed.

Oh, and BTW my pre-boil and post-boil vols were dead-on at 7.5g and 6.2g.

Still puzzled. It's a wheat beer with about 50% of the bill in wheat. Did I mention that?

 

[philipCT]

I will check the calibration on my refractometer though. I didn't realize those could be calibrated (!)

 

[philipCT]

I'm also kicking myself because this is the first time in a long time I haven't taken first runnings gravity measurements so I don't have that to refer to. Arrrgh!

FWIW - the final runnings gravity was 1.008 - exactly what I would have expected.

 

[LLBrewer]

Obviously it's not possible for the post boil gravity to be lower than preboil unless you somehow added water during some phase of the process. Do you use a leaking immersion chiller?

 

[brewkinger]

Obviously it's not possible for the post boil gravity to be lower than preboil unless you somehow added water during some phase of the process. Do you use a leaking immersion chiller?

Exactly this.. simply not possible for your gravity to go down like that.
You'd have to remove a lot of sugar for the gravity to do that.
So either you introduced water to dilute it or your refractometer needs to be checked and calibrated.

I will check the calibration on my refractometer though. I didn't realize those could be calibrated (!)

Each and every time that you brew!!!!

It does not really have to be done every brew, but as a scientist if I can take 30 seconds and calibrate a measurement tool then it is a must do for me.
The fewer things that can go wrong in my brew day the overall better a brew day it is!

 

[Natdavis777]

Yes. I make sure to stir pretty well, and mix the lower strata of wort upward to counter vertical stratification.

Even the first reading was strange to me, so I went back and stirred some more, and then resampled, and took a new measurement. I took 4 separate readings and got:

Brix - S.G. Equiv
11.2 - 1.045
10.0 - 1.040
12.1 - 1.049 and finally
12.0 - 1.048
​

I wasn't comfortable with those readings coming in so far apart, so since the last two were from a second-stirred separate sample and they agreed, that's the one I went with.

Even if the pre-boil SG was 1.040, I would expect to 10-15 points during the boil. The whole thing is weird.

Well this is what I was going to point on as well but looks like you have that strategy down. I ran into this issue when I first started, and it was because I wasnt stirring, just pulling from the top.

 

[ArcaneXor]

When using refractometers, take three successive readings of well-mixed wort. Hop particles, break material, or air bubbles can significantly throw off the reading.

 

[philipCT]

Obviously it's not possible for the post boil gravity to be lower than preboil unless you somehow added water during some phase of the process. Do you use a leaking immersion chiller?

No, I use a CFC.

I have to simply assume that my original readings were screwy somehow. I'm guessing that because this was my first grist with a lot of wheat, and I didn't "cut the mash" or stir a bit more, that I just had a lousy mash efficiency and actually ended up with a real low pre-boil gravity, and those readings were just whack.

Still bugs me that the Brix reading of the final runnings were right where I thought they'd be though. I will NEVER skip the first runnings reading again.

 

[thekraken]

Does your CFC have a leak? I imagine this would be easy to test with some food coloring.

 

[tootal]

We never take a reading out of the mash. We know where to fill on our kettle to get what we want after a 90 minute boil. We recirculate, cool and then take a reading with the clarified wort going to the fermenter. That's the reading that's important for figuring alcohol. If that reading is not what you wanted then change the recipe.

 

[philipCT]

To add fuel to the fire here, I brewed a Rye Ale the following weekend and experienced the same weird phenomenon. That recipe also had a pretty good amount of wheat in it. I'm really going to have to consider what's going on with the freakin wheat...

 

[thekraken]

What were your pre and post boil volumes?

 

[philipCT]

What were your pre and post boil volumes?

They were as expected. From the brew-log:

7.5g pre-boil. SG 1.042
This was measured with a freshly calibrated refractometer. Three readings: 1.040/1.042/1.042. So I felt pretty comfortable with it.

6.2g post-boil. SG 1.045. This was measured on a sample taken from the BK after flameout, and on a separate sample taken from the fermenter just before pitching a day later using a hydrometer.

Never seen anything like it. I can't believe no one has ever seem this before brewing with wheat. Do I have some funky wheat? Did I not grind the wheat fine enough? I grind everything at 0.045. And I did not grind the wheat twice.

FWIW - gravity readings on previous brew sessions were as expected, and gravity readings on the following weekend's brew session (Belgian Pale Ale) were also normal. No wheat in those grists.

 

[Natdavis777]

They were as expected. From the brew-log:



7.5g pre-boil. SG 1.042

This was measured with a freshly calibrated refractometer. Three readings: 1.040/1.042/1.042. So I felt pretty comfortable with it.



6.2g post-boil. SG 1.045. This was measured on a sample taken from the BK after flameout, and on a separate sample taken from the fermenter just before pitching a day later using a hydrometer.



Never seen anything like it. I can't believe no one has ever seem this before brewing with wheat. Do I have some funky wheat? Did I not grind the wheat fine enough? I grind everything at 0.045. And I did not grind the wheat twice.



FWIW - gravity readings on previous brew sessions were as expected, and gravity readings on the following weekend's brew session (Belgian Pale Ale) were also normal. No wheat in those grists.

Well, I brewed an American Wheat yesterday, 60/40 pale malt to what ratio. Pro-boil volume is 12.7gal and measured at 1.042. This was taken after the entire volume was in the BK and while waiting for the volume to come to a boil. Sample was cooked to ~ 60F when taken.

OG ended up boing 1.046 @ 10.25 post boil volume. Again, sample was taken at the end of the boil, and using my spoon to vigorously mix the wort before taking a same (same process as pre boil).

So maybe it's a wheat thing. I had to use white wheat this time as my LHBS was out of red wheat.

For the record, my past brews have all hit the numbers on the head, give or take .02 points

 

[philipCT]

Okay, so now I'm feeling slightly less insane! Thanks, Natdavis777!

I just wonder why I've never heard of this weird deal with wheat before. I'm going to post this in another thread and call it something like strange gravities with wheat.

 

[LLBrewer]

Well, I brewed an American Wheat yesterday, 60/40 pale malt to what ratio. Pro-boil volume is 12.7gal and measured at 1.042. This was taken after the entire volume was in the BK and while waiting for the volume to come to a boil. Sample was cooked to ~ 60F when taken.

OG ended up boing 1.046 @ 10.25 post boil volume. Again, sample was taken at the end of the boil, and using my spoon to vigorously mix the wort before taking a same (same process as pre boil).

So maybe it's a wheat thing. I had to use white wheat this time as my LHBS was out of red wheat.

For the record, my past brews have all hit the numbers on the head, give or take .02 points

Specific gravity is the ratio of the density of the dissolved substances in your wort to water. If your SG is 1.042 in 12.7 gallons of wort then it MUST be higher after you boil off water. It's a pretty simple concept. In your case you should have ended up around 1.052 so there is some error in your measurement process, I would guess either temperature or refract calibration/error.

 

[Natdavis777]

Specific gravity is the ratio of the density of the dissolved substances in your wort to water. If your SG is 1.042 in 12.7 gallons of wort then it MUST be higher after you boil off water. It's a pretty simple concept. In your case you should have ended up around 1.052 so there is some error in your measurement process, I would guess either temperature or refract calibration/error.

I am aware of this. Took readings with both refract (calibrated with distilled) and the hydro @ 60F. Both were the same. I even made sure I vigorously stirred the wort before taking the sample. The only other time I have ran into this issue is when I first started brewing. I wasnt stirring my solution when taking a sample, so stratification was the culprit.

Only thing I can deduce it down to is that there was an error in the Pre-boil reading. In the end, its still beer.