Brix and SG

[MattGuk]

Hi all, just a quick thing really.
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 just realised while brewing today that my pre boil gravity seems way down and reads about 1.030 on the SG scale of my Refractometer, however it's just a smidge under 8 Brix, and according to brew father that should translate to about 1.036.
What scale would be correct?

[guypettigrew]

Possibly both--it's the Brewfather conversion which is out. Using the Northern Brewer site a brix of 8 converts to a SG of 1.032.

In fact, looking closely at your picture, the Brix looks to be 7.9 and the Gravity 1.031. Which is exactly the conversion result on the Northern Brewer site.

Superb photo, by the way. Can't even begin to imagine how you took it!

Guy

[MattGuk]

Thanks guy, it was hard to get the focus but managed in the end.
I thought that I must be going wrong somewhere as usual.
I'm really struggling for consistent efficiency with my brew monk.
Some days like today, my gravity is quite low, other days its a fair bit higher, never seem to get the same BHE % which is frustrating as I am constantly adjusting my hopping rates based on what my gravity is reading.

[MattGuk]

Actually, this turned out fine, my gravity based on 70% BHE has been reached, just my pre boil hadn't for some odd reason.
Anyway 22 liters of golden ale @1.038 so should be a nice sessionable drop

[MattGuk]

Got a lovely colour

[WallyBrew]

Taken from a spreadsheet where D59 is the cell with the Brix value

=(D59/(258.6-D59/258.2*227.1)+1)*1000

this calculates 8.000 brix as 1031.80

[guypettigrew]

Definitely looks like the Brewfather calculation has an error in it somewhere.

Guy

[Cobnut]

S'funny, Brewfather is telling me that 8 BRIX = 1.031 SG and 7.9 BRIX = 1.030 SG

You sure you read that right? Or typed the right number into the calculator?

(this is with the wort correction factor left at the default value of 1.04)

[Galena]

I can confirm that Brewfather with the default correction of 1.04 gives 1.031 for 8 Brx and 1.030 for 7.9 Brix

[MattGuk]

My brew father correction was set to 0.89 which I guess was default as I never set it there.
How does one go about determining the correction factor?

[WallyBrew]

MattGuk

You might want to check your refractometer with a 10% by weight sugar solution (say 50g sugar made to a total weight of 500g with water). This is 10 brix and has a SG of 1040.

Your picture shows 10 brix as having an SG between 1038 and 1039 and I suspect if you enlarge it and draw a line across it will be 1038.6.
1038.6 is the specific gravity of a 10% by volume (g/100nl) sugar solution which is not 10 brix as brix is % by mass (g/100g).

Without checking it you will not know which scale is correct.

[Carnot]

This might help. What you are measuring is the apparent Brix.

Brix is defined as percent-weight containing in pure sucrose solution. For sugars other than sucrose, it is called the "apparent Brix" and is always a relative value. Although the designation of Brix is strictly valid only for solutions whose solids are entirely sucrose, the industry uses the measurement somewhat loosely as a reference value to measure any sweet solids in a product .( From Fischer Scinetific)

Sucrose is of course is a mixture of glucose and fructose - a di-saccharide. The wort will contain a different mixture of sugars. Its a bit like using CaCO3 for water tests. The only way to be more accurate requires calibtating the reading against known standards which is not so easy

[MattGuk]

Thanks guys, really helpful info as always

[MattGuk]

I also did one at post boil and checked against my hydro and it showed just under 10 Brix at I would say 1.037.5 as SG

[MashBag]

Thanks guy, it was hard to get the focus but managed in the end.
I thought that I must be going wrong somewhere as usual.
I'm really struggling for consistent efficiency with my brew monk.
Some days like today, my gravity is quite low, other days its a fair bit higher, never seem to get the same BHE % which is frustrating as I am constantly adjusting my hopping rates based on what my gravity is reading.

So have you got an issue with consistent efficiency or was it just the testing made you think you had a problem?

Like the Old Chinese proverb " man with two watches never know right time"