Brix and SG

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MattGuk
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Re: Brix and SG

Post by MattGuk » Tue Mar 16, 2021 11:03 am

I am now wondering if I had been chasing something that may not have been a problem.
Yes my efficiency has been lower before but looks to be around 70 for the last 3 brews.
But yesterday I saw my lower than anticipated pre boil gravity and thought my efficiency was going to be an issue, however by the end of the boil I had the right volume and pretty much hit my post boil gravity.

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Eric
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Re: Brix and SG

Post by Eric » Tue Mar 16, 2021 12:40 pm

MattGuk wrote:
Tue Mar 16, 2021 11:03 am
I am now wondering if I had been chasing something that may not have been a problem.
Yes my efficiency has been lower before but looks to be around 70 for the last 3 brews.
But yesterday I saw my lower than anticipated pre boil gravity and thought my efficiency was going to be an issue, however by the end of the boil I had the right volume and pretty much hit my post boil gravity.
Yes, you might have been chasing your tail.

If, for a moment, we ignore the complications of measuring gravity or density of beer wort with a refractometer, there is a further potential trap in readings taken from bulk wort towards the end of a sparge. Such runnings are less dense and are prone to only partially mix with more dense wort collected earlier.

I only realised this when monitoring progress on 3V, when despite extracting more from the mash, the total collected appeared to reduce. Next time, give the wort a good mixing before taking your reading.
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Re: Brix and SG

Post by guypettigrew » Tue Mar 16, 2021 1:00 pm

Eric wrote:
Tue Mar 16, 2021 12:40 pm

If, for a moment, we ignore the complications of measuring gravity or density of beer wort with a refractometer, there is a further potential trap in readings taken from bulk wort towards the end of a sparge. Such runnings are less dense and are prone to only partially mix with more dense wort collected earlier.

I only realised this when monitoring progress on 3V, when despite extracting more from the mash, the total collected appeared to reduce. Next time, give the wort a good mixing before taking your reading.
Good advice. The same is true in the fermenter. I've found that, when the wort has been slowly run from the boiler to the FV, a good stir is needed to ensure a true gravity reading is taken.

Guy

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Re: Brix and SG

Post by Trefoyl » Tue Mar 16, 2021 1:59 pm

After the boil I always take the gravity sample from the kettle. Before the boil I mix very well and sometimes boil for 15 minutes before adding hops and then cool a small sample for the refractometer.
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Re: Brix and SG

Post by PeeBee » Tue Mar 16, 2021 2:40 pm

MattGuk wrote:
Mon Mar 15, 2021 1:37 pm
... I know when using a refractometer there is a conversion factor to apply, however, my Refractometer read in both Brix and SG like most do I imagine. ...
I wish they never put those "SG" scales on refractometers. They only create confusion and do little to display anything useful.

A refractometer measures "refractory index" (an optical thing) and is generally calibrated in "Brix" (a scale derived from sucrose solutions).

A hydrometer measures density (a mass-volume thing) compared to a "reference" (usually water at the same "calibration" temperature - 20C on most brewing hydrometers).

Completely different!

For a new wort containing no alcohol and an assumed mix of sugars (mostly maltose and malt dextrin) a "SG" scale can be drawn to correlate with the Brix scale. But as soon as fermentation starts the correlation fails (alcohol is created and the sugar ratios change). The refractometer's "SG" scale become entirely useless! So the results (in "Brix") have to be passed through a calculator to allow for alcohol (but they don't allow for changing sugar ratios).

Do yourself a favour and stop using the refractometer's useless SG scale!
Cask-conditioned style ale out of a keg/Cornie (the "treatise"): https://drive.google.com/file/d/0BwzEv5 ... rDKRMjcO1g
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Re: Brix and SG

Post by PeeBee » Tue Mar 16, 2021 3:03 pm

And as Eric was saying ...

I too have recently figured out the sparged wort emptying into my boiler has an SG that is different from that measured later. Seems the slow channelling of low gravity spargings creates layering (striation) in the boiler - give it a good stir before taking readings.

(And unlike Eric, I didn't ignore the complications of measuring density of beer wort with a refractometer - hopefully I explained those complexities concisely?).
Cask-conditioned style ale out of a keg/Cornie (the "treatise"): https://drive.google.com/file/d/0BwzEv5 ... rDKRMjcO1g
Water report demystified (the "Defuddler"; removes the nonsense!): https://drive.google.com/drive/folders/ ... sp=sharing

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Re: Brix and SG

Post by MattGuk » Wed Mar 17, 2021 8:49 am

Thanks guys, so basically refractometers are useful for using as a quick reference but may not truly be gospel?
I do no sparge brewing so running of sparged wort isn't and issue and I always take my samples once everything is mixed, end of boil I whirlpool for a good 25 mins over an immersion chiller so that should be evenly mixed prior to FV transfer.
My hydrometer matches the SG on my refrac but I find it's much easier to use a refrac at higher temps as it only takes a few second to cool the 3 drops needed.

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Eric
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Re: Brix and SG

Post by Eric » Wed Mar 17, 2021 11:47 am

MattGuk wrote:
Wed Mar 17, 2021 8:49 am
Thanks guys, so basically refractometers are useful for using as a quick reference but may not truly be gospel?
We use refractometers for measurement in a complex medium, types that are so comprehensive in their formulation, untangling them might better be left to scientists, allowing brewers and beer lovers alike to concentrate on matters more easily understood and controlled. Let's just accept that using a calibrated refractometer to measure wort prior to fermentation will give a good enough approximation for our purposes.

When calibrating your reflectometer, do so with the instrument at the temperature it is used and stored to maintain that temperature. It is worth doing a comparison at zero setting and the instrument both hot and cold. An instrument calibrated from cold storage will not give meaningful readings after being sat on top of the mash tun for an hour.
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Re: Brix and SG

Post by Carnot » Wed Mar 17, 2021 9:24 pm

Just remember that your £35 (or less) refractometer is measuring an SG based on sucrose at a specific temperature. Your wort will not be anywhere near the refractive index of sucrose so do not get too hung up. Take an intial RI (refractive index) and when you think you are done a final RI. Then wait and repeat. If it is constant then do a density with hydrometer and see how it compares with the expected. I would not waste time trying to correlate RI with SG. I would rather be brewing something tasty, not ant f*cking.

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Re: Brix and SG

Post by guypettigrew » Wed Mar 17, 2021 9:51 pm

Carnot wrote:
Wed Mar 17, 2021 9:24 pm
I would rather be brewing something tasty, not ant f*cking.
Interesting hobby!!

Guy

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Re: Brix and SG

Post by MashBag » Fri Mar 19, 2021 7:59 am

guypettigrew wrote:
Wed Mar 17, 2021 9:51 pm
Carnot wrote:
Wed Mar 17, 2021 9:24 pm
I would rather be brewing something tasty, not ant f*cking.
Interesting hobby!!

Guy
LOL.
I think it might mean chase the taste not the numbers :D

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Re: Brix and SG

Post by Carnot » Fri Mar 19, 2021 7:51 pm

Mashbag

Spot on. Life is too short.

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