Specific Gravity Question

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Specific Gravity Question

Postby tony b » Sat Sep 23, 2017 8:14 am

I started another batch of Purple Crack yesterday. My initial wort sample was 14.1 Brix (1.056) just before I pitched the yeast. My estimate was that the wort was around 75F - 78F. I kept the sample with the intent of double checking it later after it cooled. I spaced and forgot until this morning. Second reading had gained 2 points Brix (16.1) for an IG of 1.064. Room temperature is around 62F. So, was the SG change due to the approx 15F temperature shift OR did I get some evaporation overnight (only about a 3 or 4 ml sample) that caused the increased reading in gravity? If it's most likely the temperature, then the reading is valid and I'll use it to estimate the ABV of the beer. If it's more likely due to some evaporation of the sample that increased the concentration, then I'll stick to the original reading.

Thoughts?
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Re: Specific Gravity Question

Postby Schwerkraftbrauer » Sun Sep 24, 2017 5:39 am

Really tough too say with a 4ml sample i wouldn't think the evaporation would of made the big difference, my vote would be the temp change
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Re: Specific Gravity Question

Postby daryl » Sun Sep 24, 2017 7:07 am

The Brewer's Friend tool shows only a two point movement for an 18 degree temperature shift for a hydrometer reading.

But that may no indication as to how the refractometer will react to the increased temp.

Can you estimate the expected OG?

SG temp.JPG
SG temp.JPG (28.07 KiB) Viewed 78 times
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Re: Specific Gravity Question

Postby karl » Sun Sep 24, 2017 7:23 am

Most refractometers have decent temperature compensation. A small sample of 4-6 ml will likely have a high surface to volume ratio, making evaporation a significant contributor to the change. I'd vote for disregarding the later measurement and using the 1.056 mg/cl as your original gravity estimate. That is, unless that number does not make sense with respect to what you expect from the extract potential and your usual process efficiency. In that case, I'd disregard both measurements and go with the expected original gravity calculated from the recipe and your typical brewhouse efficiency.

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