refractometer or hydrometer for FG

bobukbrewer · Dec 15, 2018

both are inaccurate due to the alcohol in the beer - if anybody has both they could easily calibrate one with the other - I think a final gravity hydrometer reading of 1.040 should be recorded as 1.042

xozzx · Dec 15, 2018

Not sure how a hydrometer is not accurate from alcohol? It is measuring the gravity based on displacement which should be accurate whatever the liquid.
Where are you getting this conversion from?

-Bezza- · Dec 15, 2018

xozzx said:
Not sure how a hydrometer is not accurate from alcohol? It is measuring the gravity based on displacement which should be accurate whatever the liquid.
Where are you getting this conversion from?

I think op is right. Alcohol has a lower specific gravity than water, so the act of turning sugar to alcohol means you can't truly know how much sugar is left based on the linear hydrometer scale.

peebee · Dec 16, 2018

Cor! Fight? Lets stick my oar in:

The OP isn't right! @xozzx is. Gravity measured as "specific gravity" (SG) is an absolute measure of gravity in reference to pure water (1.000). Doesn't matter what the liquid is.

Refractometers measure "BRIX", a scale based on sucrose (sugar) dissolved in water and how much that solution bends light. The relationship between BRIX and SG does change if the liquid isn't pure water (e.g. water and ethanol) and if the dissolved solids aren't sucrose (e.g. maltose, or malt sugar) hence we have to use the calculators. But I reckon using the calculators is much less inconvenient than using fragile hydrometers.

History dictates we use SG for monitoring fermenting liquids and hydrometers measure that very well.

The Baron · Dec 16, 2018

Peebee is bang right on this one. HMRC tell you to use hydrometers to measure the Specific gravity and FG for duty reasons and I am sure they would have something to say if that was not accurate

bobukbrewer · Dec 16, 2018

ok lets just focus on hydrometers the FG reading is of a liquid containing sugar and alcohol, if we assume the sugar reading is 1.040 then the say 4% alcohol solution in water will depress the hydrometer reading by say .002

commercial brewers have to have the alcohol measured chemically once a year and the HMRC allow a tolerance of 0.5% which is far wider than the discrepancy I am talking about. Theoretically a brewer could say his beer is 5%, price it as though that rate of duty has been paid, and brew it to 4.51% - perfectly legal !

Honk · Dec 16, 2018

bobukbrewer said:
both are inaccurate due to the alcohol in the beer - if anybody has both they could easily calibrate one with the other - I think a final gravity hydrometer reading of 1.040 should be recorded as 1.042

I'm curious what are you brewing with a final gravity reading of 1.040 (or 1.042 :laugh8:

) what did it start at?

love my refractometer but if I want accuracy (rarely) would use a hydrometer.

peebee · Dec 16, 2018

bobukbrewer said:
ok lets just focus on hydrometers the FG reading is of a liquid containing sugar and alcohol, if we assume the sugar reading is 1.040 then the say 4% alcohol solution in water will depress the hydrometer reading by say .002 ...

You are reading way too much into this. Your sugar solution is reading 1.040 is because it is 1.040 whether the solution is 4% alcohol, 40% alcohol or mostly sea-water. You'd be right arguing that the amount of sugar in those various liquids will be different, but that is not what you're arguing - you are saying that 1.040 is wrong. But we've always used SG and continue to do so even if it doesn't tell us exactly what we want. It's "close enough".

bobukbrewer · Dec 16, 2018

1.040 was a typo I meant 1.010

Why is a hydrometer more accurate ?

bobukbrewer · Dec 16, 2018

peebee - measure your FG with a hydrometer, add 10 ml vodka or gin to 90 ml of your "beer" and measure again............

GerritT · Dec 16, 2018

Refractometer before and during the boil, hydrometer afterwards.

bobukbrewer · Dec 16, 2018

in the UK 0.5% abv beer is labelled alcohol free..............

ACBEV · Dec 16, 2018

peebee said:
pure water (1.000). Doesn't matter what the liquid is.

peebee is spot on... A good hydrometer is calibrated to 1.000 (pure water). It doesn't matter whether you start with pure water or notionally mud puddle water which reads 1.002. The measurement is between the starting and ending of the process, you don't need to account for the mud content, if you did the calculation would be wrong.

peebee · Dec 16, 2018

bobukbrewer said:
in the UK 0.5% abv beer is labelled alcohol free..............

I'm giving you a bad day?

0.05% can be considered alcohol-free in the UK. 0.5% is in the low-alcohol bracket. Once-upon-a-time kids could buy "shandy" and the like at 0.5%ABV but that changed a while back (some countries do still consider 0.5% alcohol-free).

https://www.drinkaware.co.uk/alcohol-facts/alcoholic-drinks-units/alcoholic-and-non-alcoholic-beers/

bobukbrewer said:
peebee - measure your FG with a hydrometer, add 10 ml vodka or gin to 90 ml of your "beer" and measure again............

Are you trying to prove what I was saying or what you were saying?

bobukbrewer · Dec 16, 2018

I have a bottle of beer in my hand, Panther Hopsta. The label says 0.5% alc.vol. ALCOHOL FREE

bobukbrewer · Dec 16, 2018

peebee - as always I am seeking opinions on my thinking - say one of your beers finishes at 1.010 measured with a hydrometer - take 1 ml of it and add 99 ml vodka - take another hydrometer reading - what would you expect it to read ?

Honk · Dec 16, 2018

Bobukbrewer. I think you are misunderstanding what your hydrometer is measuring.

Normally you would use a hydrometer to measure the amount of sugar in a brew before fermentation compared to the amount of sugar afterwards and the difference can be used to calculate the sugar that has been converted into alcohol. In your example your adding additional alcohol. That is Not how a hydrometer works.

(Hydrometer s do exist to measure alcohol but these are affected by the presence of unfermented sugars ie only useful for distilled spirits)

GerritT · Dec 16, 2018

Gentlemen, would the results differ by more than a few stripes? Really?

foxbat · Dec 16, 2018

bobukbrewer said:
Theoretically a brewer could say his beer is 5%, price it as though that rate of duty has been paid, and brew it to 4.51% - perfectly legal !

Carling actually did this. Their measurement methods are far more accurate than +/- 0.5% and they used that to their advantage by continuing to label the lager at 4% while actually brewing to 3.7% and paying lower tax as a result. Reference.

peebee · Dec 16, 2018

bobukbrewer said:
peebee - as always I am seeking opinions on my thinking - say one of your beers finishes at 1.010 measured with a hydrometer - take 1 ml of it and add 99 ml vodka - take another hydrometer reading - what would you expect it to read ?

Okay. I can play along to this game …

It will fall (99% vodka - will probably fall well below 1.000). And the hydrometer will correctly register that fall.

refractometer or hydrometer for FG

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