Refractometer or hydrometer while sampling?

I'm curious what the experienced wild beer homebrewers do to estimate SG when sampling. I just pulled samples from my first 2 sour beers, both 6 months old and noticed about 4 gravity point variation in different online Brix to SG/FG calculators. I don't want to take hydrometer sized samples at this point since it will create extra head space, however as I get closer to when I think the beer is ready for bottling I would like accurate measures of gravity to avoid bottling too soon.

How often do you all take gravity readings? Do some of you only use refractometers?

(By the way, I'm excited about how these beers are tasting already, the flanders red is already pleasantly acidic and has moderate red wine character and the "lambic" has already taken on a slight lemon flavor and has some light lambic character in the aroma. I wasn't expecting them to taste so good already. Bottle dregs for the win!)

If you are reading gravity of a fermented beer via a refrac, you need to use a formula to account for the error caused by the alcohol present. Here is an example of an online calculator that accounts for the error and produces a corrected value for FG when using a refractometer.

OP mentions knowledge of online calculators.

I'd say, you sort of answered your own question. Only take a large enough sample when you feel you should, based on time/headspace, etc. Otherwise you understand the margin of error is higher but you're seeing at least a fuzzy picture of what's going on. I personally am in the mode of sampling less for the same reason (O2). It helps that my aging beers hide in the closet.

youreanimpulse said:

OP mentions knowledge of online calculators.

Click to expand...

OP only mentioned Brix to SG calculators and that there was variation between hydro and refrac, so I just wanted to make sure he was aware of the additional calculation required when alcohol is present.

I'd say, you sort of answered your own question. Only take a large enough sample when you feel you should, based on time/headspace, etc. Otherwise you understand the margin of error is higher but you're seeing at least a fuzzy picture of what's going on. I personally am in the mode of sampling less for the same reason (O2). It helps that my aging beers hide in the closet.

Click to expand...

Agreed. While more data is always good, gotta reduce O2 exposure, and save volume for when it's ready. It's a balancing act. Personally, I don't check gravity of my sours until after 12 months.

Tiber_Brew said:

OP only mentioned Brix to SG calculators and that there was variation between hydro and refrac, so I just wanted to make sure he was aware of the additional calculation required when alcohol is present.

Click to expand...

Oh sorry, I see what you mean. Cheers!

Tiber_Brew said:

Personally, I don't check gravity of my sours until after 12 months.

Click to expand...

this.

i'm not in a rush to package my sours. by giving them a year i'm confident that they have attenuated sufficiently. if the gravity reading at bottling is higher than i'm comfortable with, i will cut back on the priming sugar (don't think this has ever happened, tho). thick bottles give me a margin of error to play with.

Here's my take on the subject.

Yes, one should understand that once alcohol is present, conversion is necessary to get SG, and even then, it's probably not a greatly accurate number.

However, if you're testing to monitor or verify gravity stability, then you don't need to know what that SG number is, just whether or not it is still moving, or if it's stable. So, take refractometer readings and see if they are the same from test period to test period, or if they're moving. Don't even worry about converting to SG.

When these readings are stable, and if you feel like the beer is where you want it to be for packaging, then you can take a hydrometer reading to get your FG.


With all that said, personally, I'm in the camp of leave it alone for so long that you don't need to question whether it's stable or not, just whether it's tasting right.

Tiber_Brew said:

If you are reading gravity of a fermented beer via a refrac, you need to use a formula to account for the error caused by the alcohol present. Here is an example of an online calculator that accounts for the error and produces a corrected value for FG when using a refractometer.

Click to expand...

I'm not sure refractometer readings mean crap in sour beers. The calculators out there are 'estimates', at best, of conversion to SG in standard beers. They are based on collection of data from multiple brews (basically taking data and drawing the best line through it). No real Science has gone into it, just some mathematical manipulation of collected data.

With regular beers you have basically sugars and alcohol to correct for. Yes, there are higher alcohols and complex sugars in smaller amounts that affect the result; but because they are in smaller amounts, the calculators are resonably accurate.

With Sours, you have the added variable of Lactic acid in decent proportions to affect the refractometer result, along with many other compounds in smaller amounts that are not in regular beers. This just means there is no calculator that will give you any conversion that will be consistent with hydrometer readings for sour beers. So any refractometer reading has no real use.

Agreed, lactic acid will throw off an hydrometer reading if you want to use it for abv, but it still reads specific gravity which is what we baseline everything to.

In short: I don't think refractometer readings mean anything in sour beers.

Calder said:

I'm not sure refractometer readings mean crap in sour beers. The calculators out there are 'estimates', at best, of conversion to SG in standard beers. They are based on collection of data from multiple brews (basically taking data and drawing the best line through it). No real Science has gone into it, just some mathematical manipulation of collected data.

With regular beers you have basically sugars and alcohol to correct for. Yes, there are higher alcohols and complex sugars in smaller amounts that affect the result; but because they are in smaller amounts, the calculators are resonably accurate.

With Sours, you have the added variable of Lactic acid in decent proportions to affect the refractometer result, along with many other compounds in smaller amounts that are not in regular beers. This just means there is no calculator that will give you any conversion that will be consistent with hydrometer readings for sour beers.

Click to expand...

I think you're exaggerating the degree of error in refrac readings of sour beers, especially given the purpose of these preliminary readings. Sure, there's some additional error in a refrac reading containing acid, but exactly what percent marginal error can you really expect? All refrac readings, even OG, have some degree of error, since they are designed for sugar and water - that's it. They are a means for a quick approximation without having to commit enough product to a hydro jar. Besides, anyone taking refrac readings of currently fermenting or post-fermentation beers are just looking to get loose idea anyway.

So any refractometer reading has no real use.

Agreed, lactic acid will throw off an hydrometer reading if you want to use it for abv, but it still reads specific gravity which is what we baseline everything to.

In short: I don't think refractometer readings mean anything in sour beers.

Click to expand...

I disagree somewhat. It's not exact, but it's data that can be of some use until the final reading is done via a hydrometer. Online calculators will provide an approximation which the brewer may decide to use for ballpark figures. If not, decide if it's worth an 8 oz. draw from the fermenter each time. But, like I've said earlier in this thread, it doesn't really matter anyway because I wouldn't bother checking gravity until at least 12 months have passed. Some of my sours sit for 16 months before I even pay any attention to them (other than the occasional picture for the pellicle thread).