refractometer readings

[RAZ]

Brewed a Scottish Ale today. Everything goes great according to recipe. All numbers add up during mash, sparge, boil, etc. OG is to reach 1.077, refractometer reads just where we are suppose to be. Start cool down and rack into primary, checked OG again and refractometer is now reading 1.074. What would cause lower reading on a refractometer that has ATC?

 

[ArcLight]

Brewed a Scottish Ale today. Everything goes great according to recipe. All numbers add up during mash, sparge, boil, etc. OG is to reach 1.077, refractometer reads just where we are suppose to be. Start cool down and rack into primary, checked OG again and refractometer is now reading 1.074. What would cause lower reading on a refractometer that has ATC?

How did you reach 1.077 with your refractometer?

1. What was the measurement (in Brix?), and what formula did you use to convert to SG?

2. Maybe the temperature of your sample was a bit warmer than expected and this threw the reading a little?

3. Measurements are based on a localized sugar content, maybe several inches lower its higher or lower. You need to bix it well to get a uniform reading.

 

[ktblunden]

I had the same thing happen on my last brew (first with my new refractometer). Got one reading right after the boil and a slightly lower reading after cooling. I chalked it up to not allowing the sample to cool enough the first time.

 

[ArcLight]

I had the same thing happen on my last brew (first with my new refractometer). Got one reading right after the boil and a slightly lower reading after cooling. I chalked it up to not allowing the sample to cool enough the first time.

That's my main thought. Another is the conversion from Brix to Plato involves dividing by 1.04 up to around 1.050, if you leave that out you "mysteriously" drop a few points.

Its more complex than that:

=1.000898+0.003859118*BRIX
+0.00001370735*BRIX^2
+0.00000003742517*BRIX^3


=1.000019+(0.003865613*Plato+0.00001296425*Plato^2+0.00000005701128*Plato^3)

 

[RAZ]

How did you reach 1.077 with your refractometer?

1. What was the measurement (in Brix?), and what formula did you use to convert to SG?

2. Maybe the temperature of your sample was a bit warmer than expected and this threw the reading a little?

3. Measurements are based on a localized sugar content, maybe several inches lower its higher or lower. You need to bix it well to get a uniform reading.

Thanks for the reply ArcLight. The refractometer we have has both Brix and SG scales with ATC. I believe you are correct at when we took the measurement and having sugar content at different levels. When we are testing during boil the localized sugar content shouldn't be an issue since it's basically mixing itself. Our last test was after cool down and before we added oxygen, so sugar content was more than likely not uniform. Thanks for that observation. We are going to make a similar batch in a couple weeks so we can verify that theory, but I think you are correct.

RAZ