Impossible gravity measurements

[SirSpectre]

Hey everyone,

A few months ago I picked up a Grainfather and a Refractometer.

Both have been great once I worked out the Grainfather quirks and calibrated the refractometer.

Now I have to be doing something terribly wrong in some part of brewing or measuring. I brewed a Belgian Tripel today. I got a Pre-boil Gravity reading 12 brix. Bad news. Stirred the pot a little and tried again. This time I got 15.1 Brix - about 1.061 SG. Great. Only .02 off! Much better! This was taken at about 160 F. Refractometer is temp correcting, or so it says.

Boil, add a pound of candy sugar, I visibly see about a half gallon boiled off. Chilled to 65F and stirred a little and took OG reading. 15 brix. 1.060. WTF? This time I measured with a hydrometer as well. Same reading: 1.061. I've never had this issue before the last 2 batches. Last batch I read 1.045 before and after boil. And that had 2.5lbs of candy sugar added. The FG came out correct though, and it knocks you on your ass, so I'm not sure if its a measurement issue, user issue, or effing magic.

Any ideas?

tl;dr: measured 1.061 pre-boil. Measured 1.060 post boil + lb sugar.

 

[day_trippr]

Are you adding any water post-boil? The math certainly suggests incomplete mixing...of something...leading to a non-representative sample...

Cheers!

 

[SirSpectre]

Nope. Haven't added any water. There must have been some weird stratification. I tested again 6 hours after pitching yeast. 1.076. still not quite what I was hoping, but I also hope the yeast didn't affect that number too much.

 

[day_trippr]

Reading this again, both incidences included late or post-boil sugar additions that apparently didn't register on your testing - but clearly made their contributions. So some kind of stratification on those counts, at least.

Can't explain why the boil-off didn't register a gravity change, though...

Cheers!

 

[BlueHouseBrewhaus]

Sounds like the sugar may have settled and didn't get good mixing.

 

[Biscuits]

Hey everyone,

A few months ago I picked up a Grainfather and a Refractometer.

Both have been great once I worked out the Grainfather quirks and calibrated the refractometer.

Now I have to be doing something terribly wrong in some part of brewing or measuring. I brewed a Belgian Tripel today. I got a Pre-boil Gravity reading 12 brix. Bad news. Stirred the pot a little and tried again. This time I got 15.1 Brix - about 1.061 SG. Great. Only .02 off! Much better! This was taken at about 160 F. Refractometer is temp correcting, or so it says.

Boil, add a pound of candy sugar, I visibly see about a half gallon boiled off. Chilled to 65F and stirred a little and took OG reading. 15 brix. 1.060. WTF? This time I measured with a hydrometer as well. Same reading: 1.061. I've never had this issue before the last 2 batches. Last batch I read 1.045 before and after boil. And that had 2.5lbs of candy sugar added. The FG came out correct though, and it knocks you on your ass, so I'm not sure if its a measurement issue, user issue, or effing magic.

Any ideas?

tl;dr: measured 1.061 pre-boil. Measured 1.060 post boil + lb sugar.

Highlighted in red is where I think your problem is. How I believe the refractometer with ATC works is that it only adjusts for the temp of the refractometer itself...IE if room temp is 70 degrees, then it will adjust readings for samples at that temp. If you read a wort sample at 160 degrees, the reading will definitely be off...same as your hydrometer, except it does not temp correct.

 

[SirSpectre]

Ahh interesting. Wasn't aware thats how it worked. Either way, I think everything did line up pretty good. Smell is amazing and it hit 1.024 in 2 days. Still some left to go but So far its on track. For what its worth, I did hit all my other numbers for the last 2 batches with these odd readings.

 

[Burquebrewer]

I stopped using my refractometer after running into the same puzzle. I tested it with distilled water and calibrated it as necessary. I had used it on at least seven or eight batches with no problem. Then it just stopped being reliable for whatever reason. I thought the reading on a fresh, unfermented wort was strange so I checked it against my hydrometer and there it was?! Not sure why or how it was off after a calibration, but it's been in the box since....

 

[passedpawn]

I've been using a refractometer for years without this issue. I'm usually looking for a ballpark to decide what volume I want to boil to, to reach my desired FG. But it's always worked out perfectly. I usually do a hydro after chilling and when I'm transferring to carboys and everything makes sense.

I'm guessing there's some stratification issue here.

Next time I brew, I'm going to a pre- and post-chill refract measurement and see how they compare. I think there's a 4% volume change over that range, so I'd say that means there should be a 4% density change. However, I'd guess that the sample cools very quickly when it hits the thermal mass of the refract, so the actual difference would be much less than that, maybe negligible.

 

[Burquebrewer]

I'd guess that the sample cools very quickly when it hits the thermal mass of the refract, so the actual difference would be much less than that, maybe negligible.

True. I don't think temperature had anything to do with it. I only add a drop or two of wort to the refractometer. Can the amount and type of light have something to do with the reading (sunlight vs. bulb??) Another thought is that maybe the gravity of the wort varies somewhat throughout the BK while it is cooling?

 

[Bobby_M]

Evaporative concentration of the sample. Pull samples with a pipette and run bulb under cold water for 15 seconds first.

 

[passedpawn]

Evaporative concentration of the sample. Pull samples with a pipette and run bulb under cold water for 15 seconds first.

Maybe. Easy to test. Not obvious to me that the pipette will make a difference unless it's capped immediately. I'm no chemist.

 

[Bobby_M]

I have tested it and it makes a noticeable difference. I try to use the smallest pipette that I can get away with. It matters even more to me now that I splurged on a digital refractometer so the sample doesn't even get protection from the cover.

 

[TheMadKing]

True. I don't think temperature had anything to do with it. I only add a drop or two of wort to the refractometer. Can the amount and type of light have something to do with the reading (sunlight vs. bulb??) Another thought is that maybe the gravity of the wort varies somewhat throughout the BK while it is cooling?

Wort stratifies rapidly in the BK and it requires far more stirring than you would ever think to mix it well. I usually stir for a full 2 minutes before taking a Refrac reading and it has greatly stabilized my readings. Mine were all over the place before someone explained this phenomenon to me too.

 

[Burquebrewer]

Wort stratifies rapidly in the BK and it requires far more stirring than you would ever think to mix it well. I usually stir for a full 2 minutes before taking a Refrac reading and it has greatly stabilized my readings. Mine were all over the place before someone explained this phenomenon to me too.

Thanks!