Source
r/Homebrewing•
beardedbread

Refractometer Reading Variance

I just brewed a big double NEIPA. Usually, I pull a sample directly from the boil right after 60 minutes and put the dropper end into some cold tap water while I whirlpool. After about 20 minutes, I checked the reading and it was 1.076. Another hour or so passes and check it again. It's 1.080. What's the more accurate reading? It's difficult to check the temp with that little amount of liquid. Has anyone else encountered this? Any insight is appreciated.

Posted Apr 20, 2018, 9:44 PM UTC

413
Oginme•

Unlike hydrometer samples, refractometer samples usually do not need to be chilled down. The thermal mass of the refractometer will quickly chill the few drops of wort down to room temperature.

I usually take about 3 to 4 readings on the refractometer to make sure that I am getting a good sampling of the wort when taking a sample for gravity. Also make sure the wort is fully cleaned from the refractometer. I've found that just wiping often leads so some dried sugars left on the surface of the prism which slowly causes your reading to increase. This will happen much quicker when you use it as I do with hot wort, but it happens with room temperature wort as well.

5
Stringbean1982•

100% agree on taking more than one sample. How much fluid is actually in a drop?

2
Busted_Knuckler•

Approximately 1/30 of a ml. Depending on the SG of a liquid, 25 to 35 drops from a standard dropper is 1 ml.

Source - wife is a pharmacist.

3
sxeQ•

Does bits of grain floating in the wort throw off the reading?

1
Wadofmeat69•

What was the temp difference between the readings?

2
beardedbreadOP•

I'm not sure. I thought they were both very close to room temp, probably about 68?

1
Wadofmeat69•

Could be a sugar concentration issue. The first may have had poor distribution compared to the second. About the only thing I can think of.

2
Stringbean1982•

Most refractometers are already adjusted for temperature. I would be venture that it is due to the small sample size that you are using to check your concentration. Wort is not a homogeneous substance, so there will be variations. You should take more than one reading when using a refractometer and I always rely on a hydrometer when checking my actual OG.

1
Wadofmeat69•

Mine is ATC but there are variances in hot wort temp and room temp wort. Online calculators work to hash it out. For the OP my guess is it’s a sugar concentration issue between the 2 samples.

1
LukeWarmCage•

How are you pulling your samples, and how are you delivering the samples to the refractometer?

Also how are you zeroing the refractometer and how often do you check it?

1
h22lude•

Evaporation! The reading that you take closest to removing the sample will be the most accurate.

Edit: And I am assuming you checked the same sample that you saved from the first reading

1
beardedbreadOP•

That makes too much sense. 1.076 it is. Thank you!

1
i_cant_mathematics•

The gravity will increase as you boil off water.

-1
h22lude•

The sample was pulled at the end of the boil. Both readings were taken with the same sample just 20 minutes apart.

1