Refractometer reporting higher OGs than my hydrometer

[kevstev]

So I recently bought a refractometer. I love the precision of the measurements, and the ability to make multiple readings without losing entire beers.

However, without changing my process at all, I am finding that my last two brews have come in at or over the target initial gravity, where my (now broken) hydrometer always used to show me missing by anywhere from .02-.06. I BIAB, so I was never too broken up about it when using kits. Unfortunately my refractometer replaced my broken hydrometer, so I can't do a direct comparison. I should also add that I do check it for calibration before I use it.

Is there an explanation for this? Is it possible that my old hydrometer was off, or maybe I wasn't correcting enough for taking a reading when the wort was around 80 degrees?

 

[ajdelange]

Precision is one thing. Accuracy another. Refractometers are, despite their popularity, not the greatest for use in brewing. For OG they are often pretty close to correct (i.e. within a couple tenths of a °P) but sometimes they are off by a degree or even more. There is no way to tell which worts give the bad readings. After fermentation starts all bets are off as the alcohol pushes readings high. There are lots of formulas out there that attempt to compensate for this but any reading based the the refractometry of fermented beer must be considered approximate. Refractometery can be used for fermented beer but the instrument must be calibrated for the beer being measured by another method (hydrometer, densitomer...). 'The beer' in this context doesn't mean the particular batch but rather the recipe. IOW if you calibrate against one batch of your Burton Ale you should be able to accurately measure subsequent batches of that same beer. Not only can you get AE measurements in this way but ABV (provided that yoy calibrate for ABV as well).

 

[Bobby_M]

Without being able to do direct comparisons, there's no way to be sure it's different. Even so, extraction efficiency varies from batch to batch, especially as OG targets shift up and down.

 

[ChuckO]

Since by definition refractometers measure the refractive index of the solution and not the specific gravity they are an indirect measuring tool. Various sugars have different refractive indexes even at the same specific gravity. A wort with more fermentable sugars will have a different Brix reading from a wort with more body and umfermentables even though they both have the same SG reading.

I use the refractometer for relative readings wile mashing, sparging and pre-boil. I take both refractometer and hydrometer readings after the boil for comparison. During fermentation I will use the refractometer only to see that things are progressing and to check for completion of fermentation. I then take another hydrometer reading before bottling.

I have found pre-fermentation variations of 1-2 Brix for worts of the same specific gravity.

 

[kevstev]

Since by definition refractometers measure the refractive index of the solution and not the specific gravity they are an indirect measuring tool. Various sugars have different refractive indexes even at the same specific gravity. A wort with more fermentable sugars will have a different Brix reading from a wort with more body and umfermentables even though they both have the same SG reading.

I use the refractometer for relative readings wile mashing, sparging and pre-boil. I take both refractometer and hydrometer readings after the boil for comparison. During fermentation I will use the refractometer only to see that things are progressing and to check for completion of fermentation. I then take another hydrometer reading before bottling.

I have found pre-fermentation variations of 1-2 Brix for worts of the same specific gravity.

Wow, that's quite a bit. I guess a refractometer isn't exactly the godsend I thought it is.

 

[kevstev]

Precision is one thing. Accuracy another.

I know, I was quite careful with my words .