Hydrometer/Refractometer (Agree but don't...)

[Franky]

I just purchased a new hydrometer a couple days ago. This one has Brix included on it. I purchased it because I was afraid my refractometer might be off.

I brew small 1.5 gal batches so taking hydrometer readings take up to much of my beer.

Anyway...to the point. Yesterday I bottled a batch of beer. I took my sample and my hydrometer read 1.013. Took a sample from that and put it on my refractometer and got 10 brix. Entered all the info in at Sean Terrill and got exactly 1.013. Great I thought everything is right on.

However, while putting my hydrometer away I happened to notice on the Brix side of it that 1.013 is less then 5 Brix.

Could anyone explain why this is. Again, when I took all my measurements both the hydrometer and refractometer agreed. However, the Brix on the hydrometer does not agree with my refractometer.

Have I confused you enough yet? Hopefully this makes sense to someone and they can explain it to me.

I'm guessing that it has something to do with the wort correction factor that is used on Sean Terrill...

Thanks in advance to those who can explain this to me.

 

[McKnuckle]

This is because of the alcohol in your post-fermentation sample. In really simple terms, multiply Brix x 4 to get approximate SG. But that only applies when no alcohol is present. That's what the scale on your hydrometer depicts - straightforward liquid with no alcohol.

The 10 Brix you measured is in a fermented sample with alcohol in it. I imagine that the calculator on the site you reference takes that into account, and produces a corrected value for SG. (This is not wort correction; that's something else.)

See if this site helps produce a similar result. You'll need your OG in Brix, too - or estimate it by dividing OG in SG by 4:
http://www.northernbrewer.com/learn/resources/refractometer-calculator/

 

[Franky]

Thanks McKnuckle for the reply. Northern Brewers calculator is giving me the same thing pretty much as the other calculator.

OG: 1.083 or 21 Brix
FG: 1.013 or 10 Brix

What I still don't get is...How come my refractometer reads 10 Brix and my Hydrometer reads 4.7 Brix for FG. That is pre entering anything into any calculator or formula.

Again if I enter it into either calculator at 10 Brix (my refractometer reading) then both the refractmeter and the hydrometer agree that it is around 1.013. Sean Terrill calculator says 1.013 and Northern Brewer's says 1.010.

 

[balrog]

I think because the paper in the hydrometer is set to show you Brix and SG in sugar solution. No alcohol. Same reason you need to use Sean Terrill's (or NB's) calculator for when you are not measuring a sucrose or sugar solution but have alcohol present.

 

[BlueHouseBrew]

As previously noted, the reason for the discrepancy is the alcohol in the solution; however, it is your refractometer that is giving you the (most) "flawed" reading. The refractometer measures the refractive index of the solution. More sugar = higher refractive index = higher brix reading. However, alcohol in the solution will also increase the refractive index. Therefore, when measuring a fermented product, the refractometer will read higher than the actual sugar content. The post-fermentation calculator you are using to get the SG of 1.013 corrects for this.

To see what the (roughly) equivalent brix of a SG of 1.013 is, you would need to use the pre-fermentation type calculator. The Brewer's Friend calculator shows a brix of approximately 3.2, which is likely about what your hydrometer reads.

 

[Franky]

Would that not be the same for the refractometer? Which then should also be reading 4.7 as the FG along with the hydrometer or the other way around hydrometer read 10 like the refractometer.

The reason I ask is aren't both the hydrometer with it's brix scale and the refractometer set to show you brix and sg in sugar solution, not alcohol. In which when I measure my FG both the brix on the hydrometer and brix on the refractometer should say the exact same thing. However they are not just a little off they are way off from each other.

Unless the people who manufactured the hydrometer already put their own correction in for alcohol. However, this would not make any sense I don't believe.

 

[Franky]

Thanks BlueHouseBrew. I was starting to think that might be what it is. I think you just explained it to me. Although it still seems odd as I got a reading of around 4.7 Brix on the hydrometer.

I guess the important thing is I'm not going crazy and my refractometer plus the calculator is giving me consistent readings with my hydrometer. So I guess I need not worry to much.

 

[BlueHouseBrew]

The measurement "error" would not work the same with the hydrometer, because it measures the density of the solution, not the refractive index. Indeed, the error works the opposite way with the hydrometer; i.e., it reads lower than the actual sugar content; because alcohol is less dense than water. This is usually disregarded, however, because taking the SG of the final product with no correction for the presence of alcohol gives you the apparent attenuation (versus the actual attenuation) which is the measure most frequently used.

All of the reference materials that I have seen, calculators and charts, state that the brix equivalent of 1.013 is 3.3 (my earlier estimate of 3.2 was a little off). So, if you look at your hydrometer's scale, 1.013 SG should be roughly 3.3 brix. If it isn't, I would guess that the scale is off.

 

[Franky]

BlueHouseBrew you are right and I'm wrong. I just fished out my hydrometer from storage and it is indeed 3.3. Thanks so much! Truly appreciate it.

 

[pablosbrewing]

Would that not be the same for the refractometer? Which then should also be reading 4.7 as the FG along with the hydrometer or the other way around hydrometer read 10 like the refractometer.

The reason I ask is aren't both the hydrometer with it's brix scale and the refractometer set to show you brix and sg in sugar solution, not alcohol. In which when I measure my FG both the brix on the hydrometer and brix on the refractometer should say the exact same thing. However they are not just a little off they are way off from each other.

Unless the people who manufactured the hydrometer already put their own correction in for alcohol. However, this would not make any sense I don't believe.

Neither instrument corrects for alcohol presence - a 1.050 wort fermented down to 1.010 does not mean you fermented out 80% of the sugar

They both require a calculator to measure either actual sugar remaining, or alcohol present.

For a hydrometer the correct scale is specific gravity, for a refractometer the correct scale is Brix. Dual scale of either instrument is a crime in my opinion

 

[Franky]

Neither instrument corrects for alcohol presence - a 1.050 wort fermented down to 1.010 does not mean you fermented out 80% of the sugar

They both require a calculator to measure either actual sugar remaining, or alcohol present.

For a hydrometer the correct scale is specific gravity, for a refractometer the correct scale is Brix. Dual scale of either instrument is a crime in my opinion

I hear you...that is why I didn't even look at the brix on my hydrometer at first. It only caught my attention as I was putting it away. That got me to thinking why are they so off. Then BlueHouseBrew helped me sort it out. Explaining about refraction etc.

I agree that is why my refractometer is only in brix. All the hydrometers that my LHBS sell have brix on them...