Refractometer versus Hydrometer

[Richard Kutschman]

I have a batch of pale ale fermenting.

I used only my refractometer (NorthernBrewer) to test my OG (1.050).

Fermentation appears to have stopped on Day 7, so I took a few drops to sample, again with refractometer (temp 68°). Read 1.024 (target is 1.012). I was confused wh I was so far off.

I drew a larger sample and used my hydro meters (3-pc set from NortherBrewer). First hydrometer read 1.010. I used the second that had a more tights scale that corresponded. It read 1.012.

I retested with my refractometer - 1.024.

I thought maybe it needed calibration, so I used some distilled water - 1.000.

My question is: what could be going on with refractometer? Should I just forget it and use only my hydrometers? Seems way less that can go wrong with them.

Thanks.

 

[Beholder]

I have a batch of pale ale fermenting.

I used only my refractometer (NorthernBrewer) to test my OG (1.050).

Fermentation appears to have stopped on Day 7, so I took a few drops to sample, again with refractometer (temp 68°). Read 1.024 (target is 1.012). I was confused wh I was so far off.

I drew a larger sample and used my hydro meters (3-pc set from NortherBrewer). First hydrometer read 1.010. I used the second that had a more tights scale that corresponded. It read 1.012.

I retested with my refractometer - 1.024.

I thought maybe it needed calibration, so I used some distilled water - 1.000.

My question is: what could be going on with refractometer? Should I just forget it and use only my hydrometers? Seems way less that can go wrong with them.

Thanks.

Alcohol presence adds an offset for refractometers - fortunately, this can be accounted for if you know your OG.

Calculators can do the heavy lifting, such as https://www.brewersfriend.com/refractometer-calculator/

 

[mongoose33]

My question is: what could be going on with refractometer? Should I just forget it and use only my hydrometers? Seems way less that can go wrong with them.

Thanks.

Nothing's wrong w/ the refractometer. They aren't designed to test gravity in liquids with alcohol, which throws off the reading.

 

[dmtaylor]

Very simple answer:

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

 

[Richard Kutschman]

Wow! Now feel dumb! Thanks all. So, refractometer works fine for my OG but need to “correct” if going to use for FG. Need to figure out how to use the brewersfriend app. Confused me a bit.

 

[shetc]

This one is pretty straightforward: https://www.northernbrewer.com/pages/refractometer-calculator

 

[BrewMan13]

Also note that the original refractometer reading may need to be corrected for as well, as there is more in wort than just sugar and water. It's called the wort correction factor. There is no one formula since every tool is a little different, and the way to figure out your own can be complicated. I ended up just measuring the OG with the refractometer and hydrometer side by side for a few batches, and found the refractometer was measuring 3 points high consistently, so I subtract by that amount now.

 

[Beardless]

Don’t feel dumb- if you are part of AHA or get Zymurgy magazine, this question is brought up in the May/June 2019 issue again (page 27- Refractometer Woes).

I never understood it either, so I’ve always used the refractometer between mash and boil only, hydrometer anytime after I add hops (always thought they threw off the number). Really hurts grabbing multiple samples and feeling like I’m wasting volume, maybe now I won’t have to with all these responses.

 

[McKnuckle]

Refractometers seem like a great advanced instrument compared to a floating thing in a plastic tube, but the above idiosyncrasies reveal why they just require too much d * king around for precision measurement of wort/beer.

I find the refract most useful for gauging FG stability, i.e. whether gravity has continued to drop over a few days, but not for measuring an actual discrete numeric value.

As for use during the mash to get pre-boil gravity, I ditched it in favor of the hydro, since I can just dump the hydro sample back into the boil. During the entire life of the beer, I end up taking one full hydrometer sample for OG that I discard.