(Digital) Refractometers and Haze

[butterblum]

I have been brewing hazy IPAs only for about the last 8 months, but have noticed a repeated issue and am curious if others have run into the same thing.
I bought an Anton Paar SmartRef - which I have been mostly happy with - except that I have found it to be unreliable when measuring the gravity of a hazy wort sample.
All samples are free from trub, are at room temperature, and were pulled from the fermenter right after filling (no stratification) - so no issues there. However, my starting gravity persistently reads low if I try to measure it after the dry hop. For example - I measured the post-boil gravity of a recent session beer to be 1.051. After chilling (and adding dry hops), the final beer should have measured 1.053 (based on cooling shrinkage) - however the refractometer spit out 1.048 for the now hazy sample. The same thing just happened again on a recent batch - I have been using quite a bit of adjuncts, and have also used heavy whirlpool additions - 4 to 5oz for a 6.5 gallon batch.
And no - there is not a leak in my counterflow chiller diluting the wort.
Is this a known issue with refractometers (analog or digital)? Any ways around it? Would it be better to treat the post-boil sample as the correct value and then calculate OG manually, using the pre-chill and post-chill volumes?

 

[doug293cz]

Refractometers don't measure specific gravity, they measure the refractive index of the sample. Anything that affects the optical properties of the liquid can affect the "measured" specific gravity. Use a hydrometer if you want an accurate specific gravity, as those respond directly to density of the liquid.

Brew on

 

[tracer bullet]

I've found if I let my sample sit 10-15 minutes, the refractometer will match the hydrometer. Close enough for me to move on anyhow. Otherwise, yes, they are off, for the reason Doug mentioned.

 

[FogHTX]

You'll likely find that they match if you filter the sample. I generally use either a V60 coffee filter or a syringe filter. Removes suspended particles and also degasses the sample which is helpful as well. I have both the EazyDens and SmartRef and they agree very well on filtered samples.

 

[tracer bullet]

You'll likely find that they match if you filter the sample.

Interesting idea. I'm sure you're right. I usually have time to wait but if I'm ever in a hurry I'll try this.

When I check pH I'm typically not expecting to make any changes. It's more for record keeping, if I repeat a recipe I'll have the pH recorded for the next time and know if I should try to change the additions a bit to bump myself up or down, or leave things alone.