Hydrometer Reading Confusion

[KthuluBrew]

We have created a brew of cider. Our initial hydrometer readings goes as follows:

• 1.056 Gravity
• 7.5% ABV
• 13.8 Brix

Our problem is we are getting two different readings off the the same internet calculator for ABV.

• Brix Calculator https://www.brewersfriend.com/brix-converter/ at 7.5% ABV
• Gravity Calculator https://www.brewersfriend.com/abv-calculator/ at 7.35% ABV

What would be the best way of calculating ABV of a brew?

 

[Silver_Is_Money]

Alcohol calculators can only provide estimates. The two estimates you indicated above are in close agreement, but neither is (or can be) correct in the analytical sense of the term "correct", sans for the case of blind squirrel luck, since they involve zero chemical analysis.

 

[Silver_Is_Money]

The above said, the immediately below linked more sophisticated BF refractometer calculator (which allows for a corrective factor, generally presumed on first assumption to be 1.04 for beer and 1.00 for wine) delivers 7.35% when one assumes a corrective factor of 1.00, and a final Brix of 5.21 (an ending gravity of 1.0000).

https://www.brewersfriend.com/refractometer-calculator/

As an aside, I ran this through Novotny's quadratic method and it also derived 7.35% for a corrective factor of 1.00, and a final Brix of 5.21 (an ending gravity of 1.0000). This may indicate that BF has transitioned their refractometer math-model at this link from Terrill to Novotny. Novotny quadratic is (in my opinion) a better math model.

This improved agreement does not alter the fact that they are all merely math-model estimates.

 

[RPh_Guy]

You need to also measure the FG to determine ABV.

 

[Silver_Is_Money]

You need to also measure the FG to determine ABV.

Agreed! I made the presumption that the OP is looking forward to (I.E., presuming) an ending gravity of precisely 1.000...

This idealized FG indeed may not be the case. Also, the case for cider in conjunction with the OP's specific refractometer may not be that the corrective factor of his instrument is 1.000.

 

[cubalz]

Starting gravity - Finished gravity x 131=abv

 

[Silver_Is_Money]

Starting gravity - Finished gravity x 131=abv

This is the weakest of the math models. And least accurate.

 

[cubalz]

This is the weakest of the math models. And least accurate.

I appreciate you taking the time to bash me. I was just trying to help.

 

[RPh_Guy]

I was just trying to help.

I think you did help by bringing up a commonly used equation. Silver also helped by pointing out that it isn't very accurate compared to others. Discussion is healthy. I'm sure he wasn't trying to hurt your feelings.

 

[Silver_Is_Money]

I think you did help by bringing up a commonly used equation. Silver also helped by pointing out that it isn't very accurate compared to others. Discussion is healthy. I'm sure he wasn't trying to hurt your feelings.

There was zero intent to bash. This is after all the science forum, and on this forum things are often expressed rather directly and bluntly, albeit that often this seems a bit terse to those from a non-scientific background. Our lot would certainly not make for the best group of socialites, comedians, or human resource types.

 

[KthuluBrew]

There was zero intent to bash. This is after all the science forum, and on this forum things are often expressed rather directly and bluntly, albeit that often this seems a bit terse to those from a non-scientific background. Our lot would certainly not make for the best group of socialites, comedians, or human resource types.

I appreciate the both of your answers. I have actually seen that equation while researching online but did not use it. I also did not know that it wasn't the most accurate of the formulas available!

 

[KthuluBrew]

The above said, the immediately below linked more sophisticated BF refractometer calculator (which allows for a corrective factor, generally presumed on first assumption to be 1.04 for beer and 1.00 for wine) delivers 7.35% when one assumes a corrective factor of 1.00, and a final Brix of 5.21 (an ending gravity of 1.0000).

https://www.brewersfriend.com/refractometer-calculator/

As an aside, I ran this through Novotny's quadratic method and it also derived 7.35% for a corrective factor of 1.00, and a final Brix of 5.21 (an ending gravity of 1.0000). This may indicate that BF has transitioned their refractometer math-model at this link from Terrill to Novotny. Novotny quadratic is (in my opinion) a better math model.

This improved agreement does not alter the fact that they are all merely math-model estimates.

Thank you, I'll have to do some research on this!

 

[KthuluBrew]

You need to also measure the FG to determine ABV.

My apologies. FG was 1.000

 

[dmtaylor]

This is the weakest of the math models. And least accurate.

Pretty damned close for most intents and purposes, and elegant in simplicity.

For refractometer measurements, I'm very much a proponent of Novotny, which is what Brewer's Friend uses. Note: In my experience, the Correction Factor for cider is different from that of wort. For wort, my factor is 0.99. For cider, it is 1.04. YMMV.