Hydrometers and Refractometers

[Glenn Mitch]

Hi all, sorry if these questions seem stupid and a little basic, but I'm very confused. Hope you can find time to put me right.

I currently live in Malaysia, which is quite a backward country regards Home brew. In fact, I can't find one home brew store anywhere in country. There are online stores though, that sources most of their products from China (enough said).

I recently bought from one of these online outlets, a dual scale refractometer (Brix + S.G) and also a 3 piece alcohol hydrometer which has scales indicating Alcohol content only.

Ok, onto the questions:-

1. Can the correctly ranged hydrometer, read Alcohol content directly. I used distilled water at 20 deg C to check zero accuracy, and found it spot on. I then tried to check a sample of Guinness stout from a bottle, also at 20 deg C, whose ABV was shown on the label to be 6.8%. The result totally blew my mind. The Hydrometer instead of sinking, rose high above the zero ref. Pic attached. Anybody know what's going on?

2. Re Refractometer. I used same Guinness sample to test the refractometer. I set the zero using distilled water at 20 deg C and all seemed OK. I then used the Guinness sample, also at 20 deg C. The measured Brix was 7.8 and measured S.G was 1.028. Using online calculator for converting Brix to ABV, resulted in result of just under 4% ABV. Then tried another beer sample which has actual ABV of 5% and after calculation, result was 2%. Between the 2 samples, it seems there is a consistent error of 3 % ABV. My question is, am I mistaken in thinking that I can use the refractometer to measure actual S.G of a finished beer and then calculate equiv ABV. From what I've read on this website, I'm starting to think that the only way to use it it measure ABV, is to take 2 readings, one before fermentation starts and one when it's finished prior to bottling. Either that or the equipment I've bought is substandard and useless.

Any help greatly appreciated

 

[Positronic_Matrix]

I believe the issue is that your beer is carbonated. As the carbon dioxide comes out of the beer, the bubbles stick to the hydrometer, lifting it out of the liquid. I bet the hydrometer would be accurate if you let the beer go flat before you took a reading.

 

[Glenn Mitch]

I believe the issue is that your beer is carbonated. As the carbon dioxide comes out of the beer, the bubbles stick to the hydrometer, lifting it out of the liquid. I bet the hydrometer would be accurate if you let the beer go flat before you took a reading.

Big Thanks, I'll give that a go next

 

[BrewnWKopperKat]

Welcome to the forums!

1. Can the correctly ranged hydrometer, read Alcohol content directly?

For most hydrometers, the answer is likely to be "no". Typically, ABV is calculated using OG and FG. https://www.brewersfriend.com/abv-calculator/

2. Re Refractometer.

Refactometers typically do not read FG correctly due to the presence of alcohol. A correction factor needs to be determined for the specific brand of refractomenter. https://www.brewersfriend.com/refractometer-calculator/

 

[RM-MN]

If you need to know the final gravity you would use a hydrometer. Using a refractometer with the proper correction calculation will be close. If all you really want to know is if the beer is done fermenting so it is ready to bottle, either work fine as what you are checking then is if there is a change over 2-3 days or not. No change says it is safe to bottle.

 

[cactusgarrett]

Refactometers typically do not read FG correctly due to the presence of alcohol. A correction factor needs to be determined for the specific brand of refractomenter. https://www.brewersfriend.com/refractometer-calculator/

This. You need to know the OG, and use the correction factor when using a refractometer. The issue related to your first question is the CO2 buoying the hydrometer. Even with an accurate FG, you still need to know the OG to determine the ABV%.

 

[Miraculix]

Aaaand just to add, the correction factor is neither linear nor the same for each beer. In other words, it might give you a result which is fairly close, or far off. That's why refractometers are usually not used to determine fg.

Hydrometer is the best solution imo. Measure og and measure fg after fermentation finished and calculate your abv based on these two numbers.

 

[Positronic_Matrix]

Here’s a great Brulosophy post on the accuracy of a refractometer versus a hydrometer. As folks said in this thread, the refractometer measures sugar in water. The alcohol in the FG reading skews the results and thus requires correction. Using an online tool (a link is in the post), he was able to consistently and accurately correct for the alcohol, although prefers use of the hydrometer.

http://brulosophy.com/2014/09/08/refractometers-are-they-really-worth-it/

 

[cactusgarrett]

Refractometers at the back end of processes are integral for the small-volume brewer, though. Hard to burn a hydrometer's worth of sample anytime you want to take a reading if you've only produced 4L of beer.

 

[Bubbles2]

Hydrometer is what you have that will tell you where you (ended up at, or start at), for sugar start and what is left or end at, and then using math of 13.1 "I think it is" to multiply the difference to get a ABV.

When making Moonshine and you keep distilling it you use an Alcoholmeter. Which is probably what is used to measure or verify what you are doing as you do not know the start value and can only measure the end value and have nothing to subtract to then multiply the ABV.

 

[BrewnWKopperKat]

Refractometers at the back end of processes are integral for the small-volume brewer, though. Hard to burn a hydrometer's worth of sample anytime you want to take a reading if you've only produced 4L of beer.

If you had said "many small-volume brewers", I would have quietly agreed. But you said "the small batch brewer".

So I'll politely offer an alternative (and maybe someone will offer a third) based on the way that I brew.

For small volume brewing (< 2.5 gallon batches), I

1. decide how much beer I want: 6 pack? 12 pack?
2. pick an appropriate fermentation vessel
   • 6 pack? 1 gal carboy
   • 12 pack? 2 gal food grade bucket
3. scale recipe to deliver appropriate amount of wort to the packaging station for either 6 or 12 bottles
4. add additional volume for hydrometer readings, losses during bottling (beer left in siphon, at bottom of bottling bucket, ...)
5. add additional volume if hop additions are "large"

 

[bracconiere]

3 piece alcohol hydrometer

3 piece? so a cylinder some booze and a alcohol hydrometer? alcohol hydrometers are for distilled spirits, not beer...and refractometers don't work with fermented beer....to tell Alcohol content you need both OG, and FG readings....or if it's dry you can use vintometer...might be some tools i'm forgetting

(the reason your alcohol hydrometer was confusing, is because i doubt guiness is fermented dry)

 

[Glenn Mitch]

3 piece? so a cylinder some booze and a alcohol hydrometer? alcohol hydrometers are for distilled spirits, not beer...and refractometers don't work with fermented beer....to tell Alcohol content you need both OG, and FG readings....or if it's dry you can use vintometer...might be some tools i'm forgetting

(the reason your alcohol hydrometer was confusing, is because i doubt guiness is fermented dry)

The 3 Pieces I refer to are 3 separate Hydrometers. One ranged 0-40%, 2nd being 40-70% and last one 70-100%.

Thanks to all for the responses - A bit clearer now, sort of!!!!

 

[Qhrumphf]

Distiller's hydrometers (which it looks like you have) will indeed read actual ABV, but not in the presence of any residual carbohydrate (they're designed for measuring high proof distilled spirit). They won't read correctly in beer, even if you decarb first.

Nor will a refractometer tell you ABV, even if you correct the reading.

You can, with a *specific gravity* and not an *alcohol* hydrometer, and a refractometer, reverse engineer an OG and ABV by manipulating one of the refractometer conversion formulas. But as indicated above assumptions have to be made so while you can get close it's still an indirect approximation.

 

[BrewnWKopperKat]

You can, with a *specific gravity* and not an *alcohol* hydrometer, and a refractometer, reverse engineer an OG and ABV by manipulating one of the refractometer conversion formulas. But as indicated above assumptions have to be made so while you can get close it's still an indirect approximation.

Also a "ready to use" calculator here:

"Approximate ABV and Original Gravity from current Brix and Gravity converter"
https://www.northernbrewer.com/pages/refractometer-calculator​

for those who don't like to manipulate formulas.

 

[bracconiere]

You can, with a *specific gravity* and not an *alcohol* hydrometer, and a refractometer, reverse engineer an OG and ABV by manipulating one of the refractometer conversion formulas. But as indicated above assumptions have to be made so while you can get close it's still an indirect approximation.

damn that's what i couldn't remember, i just learned you can do that myself not long ago....