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Am I using my refractometer wrong?

It seems stupid, but I don’t know how I’m regularly so far off. It reads 0.0 (brix) with clean water @ 60 F. So I THINK it’s calibrated right, but when i take a pre-boil reading, it ends up higher than the post boil. Today i did a ryepa, the PBG was 15 brix (1.061 spec. grav.) and the O.G. after an hour boil was 10 (1.040). Clearly something is off. I thought that I didn’t need temp. correction with a refract, am I wrong? I don’t think it’s even possible for the PBG and the OG to be the same, so what’s going on here?
big mess.
Any help you can offer to unstupid my brewday would be awesome.

First thing is you need to do it with distilled water second does yours have ATC .

I haven’t used distilled water, but it does have ATC.

Regardless of ATC, be sure to ensure that the sample is cooled to room temperature.

Will taking a sample of hot wort mess up the test? or is it more a concern for cracking the glass on the refractometer?

I’ve found that hot wort will evaporate enough as you put it on the glass to change the reading by several 1/10s of a Brix. That is a source of error, but obviously not the problem you are seeing.

The most obvious cause of most gravity measurement errors is stratification. Do you mix your wort pre-boil before taking the gravity reading? If not, you might be taking your sample from a highly concentrated area and that could be the cause. Post boil that isn’t a problem, as the boil is very effective in mixing the wort.

for a long while I WAS taking my sample right from the mash, before it gets sparged. That was very high, however, I’ve since let the sparge process finish and let the wort start to boil before taking my sample, and STILL have a higher reading on the PBG than on the OG. After thinking about it overnight, it seems impossible that I’m getting the reading that I am… but I am. The only thing I can think of is that the wort temp is somehow screwing up my readings, my refractometer does have ATC, but I wonder if near boiling wort is too much for the refract to handle.

Try chilling a large enough sample for a hydrometer, then compare the cooled hydrometer reading to the refractometer while the wort is still hot and again once the wort has cooled. That should tell you whether you can trust your ATC refractometer to do its ATC thing.

If the refractometer is not ATCing, it isn’t a great chore to cool 10 drops of wort to 60 F before transferring a couple of drops.

If I’m right the wort has to be under 130 deg for the ATC to read it. I always cool mine down to about 80 deg or less .

I cool my refractometer sample using a steel shaker that is used for mixing drinks. I have a small container filled with ice water. I use a small measuring cup to pull a very small sample of boiling wort. Put the hot wort in the shaker, put the shaker in the ice water ant swoosh it around for just a few seconds, and there you have it. Cooled wort. Real fast, real simple. Even though my refractometer is ATC also, I find that this method works good.

I’ve got a buddy that had the same issue. Turns out the pipette the was using to take the post boil sample was retaining too much sanitizer.

Are you making sure that after you sanitze your pipette (Or whatever you are using to pull a sample from your post boil wort) is sanitized… and then making sure that you get as much sanitizer out as possible? I told him to squeeze several samples in and out of the pipette before drawing his true sample.

For some reason he still seems to come in a little low (Could be not using distilled water to calibrate) but he is doing much better.

Just my 2 cents…

I usually use my stir spoon, to drop a few drops onto the refract. it should be clean having been in the boil, I think my issues might be temp. related?

I keep meaning to boil a pound of sugar in a gallon of water, so I have a known value, then test the refract in hot sugar water, and again in cooler water, and see what the difference might be.

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