Refractometer vs Hydrometer Reading

[ThatYodaGuy]

I was brewing an APA and broke my trusty hydrometer before the final OG reading (pre-boil was 1.051), and of course it was a saturday, so I saved a sampling a cup and covered it in glad wrap and waited for my new Hydrometer from fleaBay.

I was given a refractometer on Monday and thought I'd give it a crack, however it was a Salinity refrractometer that SG readings and ppt (for salt I assume). it read 94ppt and 1.070, quite high I thought. However, I've just picked up my new hydrometer and it is reading an OG of 1.044!!

What is going on here? Has the sweet wort collected some random strain of yeast and stated fermenting in my trial cup?

Back to the fermenter I take an fermenting wort (5 days) reading of 1.054 from the refractometer and 1.029 from the hydrometer.

Both hydrometer and refractometer have a reading of 1.000 for water.

Anyone got any idea which instrument is out or what is going on inside the cup/fermenter?

Cheers!

 

[manticle]

Firstly your refractometer needs to be corrected for the presence of alcohol if it is fermenting. Otherwise it will read high.
Secondly if your sample was in the fridge and cold, it will read lower on the hydrometer.

Try a known sample of unfermented wort (something like 100g DME ) in 1L of water and compare the two.

Forget the salinity hydro.

 

[ThatYodaGuy]

Gah! I meant salinity refractometer. The readings were all at 20*C

 

[ianh]

You need a Brix refractometer not a salinity one, measuring sugar not salts.

 

[ThatYodaGuy]

You need a Brix refractometer not a salinity one, measuring sugar not salts.

I get that. But, as it was free and has a density measure I thought it'd do just fine. The SG matches up with the ppt on a calculator I found, so for all intents and purposes it should measure the same, and if I punch the SG (or ppt) into a calculator I should get an adjusted measure for Brix, no?

 

[ianh]

I get that. But, as it was free and has a density measure I thought it'd do just fine. The SG matches up with the ppt on a calculator I found, so for all intents and purposes it should measure the same, and if I punch the SG (or ppt) into a calculator I should get an adjusted measure for Brix, no?

Sorry my bad, I was thinking the salinity one would not have the range (was thinking sea water rather than salinity). But cannot explain your measurements, whilst once fermentation starts the refractometer reading needs a correction applied but in any case the reading is going to be lower than the initial reading. Just put it down to experience and trust the beer turns out fine.

 

[stuartf]

You may need to calibrate the refractometer. There should be a little screw somewhere on the body, make a couple of different % solutions of dex in water and see what it reads then adjust as needed.

 

[greggo]

This was explained to me some years back. Your refractometer measures sugar in water. Wort has high amounts of maltose in it so it will refract light at a slightly different angle. Usually around 3 points. Take a hydro reading of your wort and set your refracto to same.

 

[ThatYodaGuy]

Okay, so if anyone still cares...
Refractometer's definitely bust.

But, what's the go with the hydro reading 7pts lower than the pre-boil? Post boil was supposed to read 1.059, so has the unfermented wort found some yeast or what?

 

[dkaos]

Was the wort cool when you took that reading? Hydro's are calibrated at a certain temp so it may have been skewed off by that.

 

[hellbent]

You may need to calibrate the refractometer. There should be a little screw somewhere on the body, make a couple of different % solutions of dex in water and see what it reads then adjust as needed.

I agree, I test and calibrate my refractometer to 0 with distilled or tank water every time before use and nearly always need to adjust it.