Refrctometer Calibration Question

I have a new ATC refractometer with % brix and SG scales.

My question: Should I calibrate it each day I use it?

The manual for the refractometer says to calibrate it at 20C (68F). My house is 75-80F in the summer so there is no good way to get the refractometer to 68F.

This weekend I had the following experience.

1) refractometer stored throughout brewday in shade in doors in my kitchen.
2) read refractometer with distilled water. Reading was above zero.
3) dial screw to move reading to zero. Was this the right thing to do or was the reading above zero the ATC doing its job and I actually moved the refractometer out of calibration?
4) OG: refractometer = 12.8 brix (1.052 SG), corrected hydrometer 1.053 SG* I had the same experience with pre-boil gravity readings but I don't remember the numbers.

I repeated steps 2-4 many times that day. I waited varying times between placing sample on the glass and reading the refractometer. I generally waited 30 seconds to 2 minutes.

I know the difference is not much but the refractometer reading is before wort correction factor. I was supposed to divide the refractometer reading by 1.02-1.04 wort correction factor) before converting to SG since the refractometer measures sucrose content not maltose content. Based upon these common wort correction factor values I was expecting the refractometer to always be higher than the hydrometer. So I was expecting a refractometer reading of 13-13.3 brix (pre wort correction factor). That is pretty far from the actual reading and outside of the stated error of +/- 0.2 brix for the refractometer.

* I have previously (months ago) measured hydrometer with distilled water at 60F. The hydrometer was 1 point high. I subtract 1 point from the reading before temp adjustment.

I have since calibrated the refractometer after sitting in a 68F environment for 30 minutes. So my question is should I leave it alone if the reading is not 0 from distilled water next time I use it on a brew day?

Thanks!

I calibrate mine at the start of each batch. It takes a few seconds, so it's not a problem. You should always adjust to 0 if it hasn't stayed there. The thing can only stray if the temperature has changed or the adjustment screw has turned. Either way you need to get it lined back up.

Homercidal said:

I calibrate mine at the start of each batch. It takes a few seconds, so it's not a problem. You should always adjust to 0 if it hasn't stayed there. The thing can only stray if the temperature has changed or the adjustment screw has turned. Either way you need to get it lined back up.

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So am I supposed to follow instructions and calibrate it at 68F? The manual explicitly says not to calibrate at other temps.

Supposedly. The best is to always calibrate and use it at or very close to the proper temp. In case you are wondering, the ATC they advertise it for means that the unit itself automatically adjusts for it's varying temp, not the temp of the sample.

What I do is to get a small cup of ice water and another cup of water at 68. After pulling the sample from the BK I swirl the pippette in the ice water to quickly chill it down and then swirl in the 68 degree water to get it real close to 68. It only takes about 1-2 minutes total to pull a sample and get it on the refractometer.

Homercidal said:

Supposedly. The best is to always calibrate and use it at or very close to the proper temp. In case you are wondering, the ATC they advertise it for means that the unit itself automatically adjusts for it's varying temp, not the temp of the sample.

What I do is to get a small cup of ice water and another cup of water at 68. After pulling the sample from the BK I swirl the pippette in the ice water to quickly chill it down and then swirl in the 68 degree water to get it real close to 68. It only takes about 1-2 minutes total to pull a sample and get it on the refractometer.

Click to expand...

For OG measurement I just pulled the sample after the wort was chilled. It wasn't 68F (more like 75F). Neither was the refractometer. My house was 78F (I live in the deep south) in the A/C that day. I don't have a ferm fridge or other way to cool the refractometer to 68F.

kehaar said:

For OG measurement I just pulled the sample after the wort was chilled. It wasn't 68F (more like 75F). Neither was the refractometer. My house was 78F (I live in the deep south) in the A/C that day. I don't have a ferm fridge or other way to cool the refractometer to 68F.

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If you zeroed it at the same temps before reading, you will be good. Numbers are fun to play with but, in the end, they are only numbers. Be consistent in the way you take measurements and they will be accurate in relation to each other and, in the end, that's all that truly matters.

I do like to play with numbers.

Yeah, ATC is a fancy way of saying it has an aluminum housing in contact with the prism via a thermally transmittent media. This means that the prism will heat/cool the small amount of sample to AMBIANT temperature. Thats assumed to be whatever the room temp is. Understanding that, be conscious of the room temps and if you have to take readings in the AC that you want to compare to the readings you took in the garage in august, give the refract time to reach ambient temp and re-zero with water before taking the readings and don't hold it in your hand by the aluminum housing : ).

My cheap refracto has never gone out of whack, as in, I've never needed to adjust it. Expect the same.