Refractometers & Sediment

[SkyHighBrew88]

So a buddy and I were brewing today and noticed a jump from a preboil 12.5 brix to 16.0 brix over the course of a 60 minute boil (1.047 - 1.065). We were expecting, since we pretty much nailed the preboil gravity, to get a OG of 14 brix (1.057).

Unfortunately we forgot to use the hydrometer to compare before my buddy poured the wort into the carboy.

Anyways, the reason I'm guessing for this jump is from hop/trub sediment on the lens was the remaining cloudy wort from the bottom of the kettle.

This is my first time using a refractometer so I'd appreciate any thoughts on this...

 

[SkyHighBrew88]

My buddy took a quick sample & confirmed a 1.063. So maybe just a bit off...not much though.

 

[erikpete18]

Yeah, its possible that sediment would screw it up, but it sounds like the reading was fairly close. Did you stir everything well before you took the pre-boil reading? Unless you were boiling off more than you usually do (maybe due to the low humidity?), its possible that your wort wasn't mixed completely before the boil started and some of the lower gravity sparge water on the top hadn't mixed well with the higher gravity first runnings. Something to consider for next time at least.

 

[microbusbrewery]

My disclaimer is it's been a while since I was in school, so I may not be remembering things correctly. My understanding is the index of refraction is determined by the amount of soluble solids dissolved in solution. Sediment would be particles in suspension, but they're not in solution (sediment settles out, dissolved sugars do not). That said, I don't think sediment would cause it to read high or low but depending on the amount in suspension it could make it harder to read due to blocking light. Maybe someone with a degree in physics can chime in on this one.

 

[SkyHighBrew88]

I have heard that sediment will make the line a little fuzzy. I think I do remember that. Next time we'll give it a better stir & take a couple readings, maybe average them out just to make sure.

I punched the info into BeerSmith & found I would've had needed a 22% evaporation rate to get that high of a FG from preboil. I boil vigorously but daamn!

 

[rcrabb22]

I'm not sure if you brew inside or outside but most refractometers say they have Auto Temp Correction but the range is limited. Also remember ATC is not for the sample temp but for the temp of the unit itself based on the environment the refractometer is subjected to.

ATC works by the visible scale inside the unit riding on a bi-metal strip sliding the scale up and down based on the temp of the unit. Once the unit temperature is outside the ATC range of the unit the reading can be inaccurate.

I brew in the garage and leave my refractometer in the house when the temp in the garage is out of ATC range. My unit's ATC range is 10C - 30C or 50F - 86F

 

[SkyHighBrew88]

I'm not sure if you brew inside or outside but most refractometers say they have Auto Temp Correction but the range is limited. Also remember ATC is not for the sample temp but for the temp of the unit itself based on the environment the refractometer is subjected to.

ATC works by the visible scale inside the unit riding on a bi-metal strip sliding the scale up and down based on the temp of the unit. Once the unit temperature is outside the ATC range of the unit the reading can be inaccurate.

I brew in the garage and leave my refractometer in the house when the temp in the garage is out of ATC range. My unit's ATC range is 10C - 30C or 50F - 86F

Wow I had no idea about that, thanks for the info. My refractometer does have ATC but I was thinking all this time it was compensating for the sample temperature. We did however take both readings inside so that wasn't a factor. Still, I'll know to leave it inside, it's been anywhere from 16F-40F the last few days. Can't wait for summer.