Refractometer reading swings high and low during boil

I'm getting almost a completely different Brix reading every time I use the refractometer, and what's strange is that it will actually lose points during the boil. Is this caused by the heat? Or possibly the hops? Anyone else experiencing similar issues?

Thanks

Is your calibration screw loose? That's not normal. How does it compare to a hydro reading?

How much does your ambient temperature change? My instructions say to re-calibrate if ambient temperature changes by more than 5 degrees. I brew outside in Florida; so I am constantly re-calibrating throughout the brew day.

A lot of refractometers have automatic temperature correction. Maybe the samples are more/less dense depending on when or where you take the small sample from? This is a variation on the new brewers taking a hydrometer sample from the extract brew that hasn't been completely stirred to become uniform density...

If its hot where youre brewing, and you store your refractometer inside, or if the temp increases during the day, your calibration is gonna change. I keep my refractometer in my ferm fridge at 68deg and keep my calibration dH2O there too.. I check my calibration several times during the day.

My refractometer is set to work at 20 deg C, so when Im brewing in a 85-90 deg F garage, my calibration goes way off.

same thing happens with mine. i'll take a preboil reading, say 1050, then another 30 minutes into the boil and it will be way off, like 1075 or more. when i take a reading from the cooled wort going into the fermentor the readings are accurate. this is a pretty recent thing so maybe something has gone wrong with the thing.
.

I calibrate with multiple readings to make sure I have a good calibration right before my sample. Then I measure the sample over and over until I see three consistent readings. Only then will I trust what the refractometer is telling me.
Since I've started doing this, I've had zero questions of strange readings and my readings are usually a lot closer to what I'm expecting.

krazydave said:

I calibrate with multiple readings to make sure I have a good calibration right before my sample. Then I measure the sample over and over until I see three consistent readings. Only then will I trust what the refractometer is telling me.
Since I've started doing this, I've had zero questions of strange readings and my readings are usually a lot closer to what I'm expecting.

Click to expand...

Great advice!
I have similar issue on my last batch (measures was 1 °P off in 5 minutes), pretty illogical... but when I took my hydrometer sample at the end of boil it matches refractometer reading.
I"ll do it your way next time.

I have found that if I get my sample off of say my spoon it will vary a lot, but if I use the pipete that came with the refractometer it doesn't. I accredit it to evaperation of the hot wort before reaching the refractometer.

Grab a few drops in a pipet, invert the pipet and dip the bulb in a small cup of icewater for 5 seconds. Dispense it on the refractometer.

Things mentioned already. Tiny hot wort samples will evaporate water quickly and change the gravity enough to be frustrating.

ATC is not a cure all for dumping any temp sample on the prism. ATC compensates for small shifts in ambient temps, not sample temps. While the prism has enough mass to pull sample temps down pretty close to ambient, it adds enough heat that the reading can shift as you watch.