Refractometer

[Kronos]

I have a refractometer that reads in Plato does anyone know how to convert this to SG.

I have also heard that you can use a refractometer to record FG but you need to do another calculation, does anyone know what it is.

Thank you.

 

[Horners]

Online calculator will take you from Plato to SG (See Brewers Friend). IMHO only good for wort - so measuring sparge runnings, pre boil, post boil. Once the wort becomes beer and has alcohol in it, things go askew. The second calculation you refer to involves adjusting reading for alcohol content - alcohol having different optical properties. This correction seems to be based on empirical readings over a number of samples to compute an 'alcohol correction factor' so that you can estimate FG.

My conclusion on refractometer is that it is good for determining when to stop sparging, good for getting gravity of unfermented wort and therefore working out any dilution required in FV but once fermentation starts best use a hydrometer.

 

[Bigcol49]

Hi!
To properly find a Correction Factor for your refractometer you'll need about 40 brews, if I recall correctly.

 

[stz]

Irrespective of refractometers plato isn't far off brix, nominally the same to 3 significant figures and are pretty much interchangeable. Brix is the strength of sugar in solution as mass. 1 brix = 1 g in 100g solution which is handy to know if you didn't. Both are pretty much x4 anyway to put it into SG for back of a beer mat maths. Tables, online converters etc exist, but at 'normal' gravities it doesn't drift too far though clearly at 'silly' gravities you'll be quite far off. It is pretty much x4 all around 1.040ish. At lower levels it is a bit less than you'd think and at higher levels a bit more, often a read error amount tbh.

Refractometer adjustment ... man, this falls into the realm of what exactly do you want to achieve? They have a purpose in the brewery certainly, but accurate and definitive readings are pretty low down on the list.

 

[Kronos]

Thank you the comments so it looks like I am best to use the refractometer for testing before the yeast is pitched and once it has been pitched a hydrometer should be used.

 

[Honk]

You can still use a refractometer at end of fermentation to see if it's still coming down or not and using a calculator that takes into account the start reading will give you a pretty good idea where your at. Depends how accurate you need or want to be. I'm not too worried if my beer is 4.5% or 4.7% I know it's around that. Comparisons with a hydrometer reading on the occasions I've done it have led me to believe that my refractometer is pretty accurate, a lot easier to read, and only needs a drip or two to sample