Calibrate those hydrometers, people

Get one cup of distilled water, cool it to 60° F (or whatever your hydrometer says it's calibrated for), and then test your hydrometer. They usually only cost around five bucks at the homebrew store, so chances are pretty good the quality control on them is not the best. Here's mine. As you can see, it should be reading 1.000 but it's reading 1.004, so it's .004 points high, so all of the wort / beer I test with this thing has to have .004 points subtracted from the readings.

Looking at that, I see 1.000. I believe you read these from the top of the meniscus.

Good idea to make a sugar solution and do a 2-point calibration. I have 3 hydrometers and tested them @ 1.000 and 1.100. 2 of them were nearly perfect at both ends. The other read 1.002 with water and 1.111 with the 1.100 solution!

Thats an error of 11 points at high gravity. Wow.

I tested against a refractometer.

That looks like 1.000 to me too...

Read from the bottom of the meniscus

The calibration is only as accurate as your thermometer (and ability to read the instrumentation properly).

ABV and attenuation will not change so long as your hydrometer reads linearly, and the samples were taken at proper temp. You may be fooled into thinking that your efficiency is consistently low or high, but let your palate be the ultimate judge, not some lab instrument.

silvery37 said:

Read from the bottom of the meniscus

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Agreed. At least that's what I was taught by my Chemistry professor.

Yuri_Rage said:

The calibration is only as accurate as your thermometer (and ability to read the instrumentation properly).

ABV and attenuation will not change so long as your hydrometer reads linearly, and the samples were taken at proper temp. You may be fooled into thinking that your efficiency is consistently low or high, but let your palate be the ultimate judge, not some lab instrument.

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A few degrees error on a thermometer don't make 1 gravity point of difference. So, while temp does effect the reading, the accuracy of the thermometer is not very important.


As I demonstrated above, the error in one of my hydrometers was not just an offset. This error would have resulted in incorrect ABV and attenuation. I agree we are in the minutia of brewing process, but hell that's what we do here, right?

DarthMalt said:

Agreed. Looks like 1.004.

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Ray Daniels, on page 14 of Designing Great Beers, says this (I've got it opened in front of me here):

Now I'm all confused! I think I always read the top, too. Dammit, I can't even remember. More Google!

passedpawn said:

Ray Daniels, on page 14 of Designing Great Beers, says this (I've got it opened in front of me here):

"Also, read the hydrometer correctly. (The hydrometer reading should be obvserved at the top of the small meniscus thet forms around the hydrometer shaft). While this might seem simple, I did it incorrectly for nrearly six years!" [emphasis is Ray's, not mine]​

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I'll trust a science textbook. Thanks.

Unless, for some reason, beer hydrometers are calibrated differently... I'm not sure of this though.

More Google did not help. I found both answers. Perhaps it's best to read the documentation that comes with your hydrometer and do what it says. Several quotes from hydrometer instructions discussed reading the top of the meniscus. Several university and homebrew sites mention the bottom. Hell, I'll throw mine in 60 degree distilled water and use whichever side is closest to 1.000

I have 3 hydrometers. Here's my test data, all adjusted for 60F. Draw your own conclusions.

From our own wiki, these two conflicting entries:

https://www.homebrewtalk.com/wiki/index.php/Talk:Hydrometer


https://www.homebrewtalk.com/wiki/index.php/Hydrometer

Yuri_Rage said:

More Google did not help. I found both answers. Perhaps it's best to read the documentation that comes with your hydrometer and do what it says. Several quotes from hydrometer instructions discussed reading the top of the meniscus. Several university and homebrew sites mention the bottom. Hell, I'll throw mine in 60 degree distilled water and use whichever side is closest to 1.000

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Haha, I'm doing the same thing and have arrived at both answers as well. Maybe brewing hydrometers are different...

Now I'm confused.

OK, just grabbed the instructions from one of them. It says "At eye level read the figures on the stem of the hydrometer where the surface of the liquid cuts across the stem."

And yes, we're still splitting hairs. I used to care a lot about gravity readings. Now I mostly care about getting close and winding up with a good beer.

All this todo regarding the minescus is certainly splitting hairs.

But, the subject, hydrometer error, isn't: one of mine is off by 5 points at 1.050. Not the end of the world, but that's significant for those that care about measurements.

just read it the same way consistently so all your notes match your method.

the meniscus police wont raid your house if your a top reader.

in labs you read the bottom, with clear liquids or salinity reading this is easy. with beer thats darker or with a pure liquified darkness stout the guess factor is often more inaccurate than just consistently reading the top.

I guess it is splitting hairs, but in my mind if you do it the same way every time, it gives the same spread.

FWIW I read the bottom.

I also agree that if read from the same spot each time it really shouldn't matter. The difference would be noticeable when comparing notes with another brewer though.

The more I think about this, the more it makes sense that brewing hydrometers might be calibrated differently because it's easier to read from the top of a dark beer. Just throwing it out there after some more consideration. You'd think there would be a standard for all hydrometers though...

I've almost pulled the trigger a couple times on the precision hydrometers AHB sells. The range is much narrower, which I would presume (hope) results in more accurate results. Reading this makes me think I'll place an order...

Yuri_Rage said:

The calibration is only as accurate as your thermometer (and ability to read the instrumentation properly).

ABV and attenuation will not change so long as your hydrometer reads linearly, and the samples were taken at proper temp. You may be fooled into thinking that your efficiency is consistently low or high, but let your palate be the ultimate judge, not some lab instrument.

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Temperature doesn't play nearly as critical of a role in this calibration.

Problems arise if you use a refractometer for the brewing process and a hydrometer for the fermenting process, and one of those two devices is not reading right.

Or if your hydrometer doesn't read linearly, so yeah, if you really care about these things, then test the hydrometer at two set points.

So what your saying is that hydrometers are like hand grenades and horseshoes. just need to be close but not spot on

Glynn said:

So what your saying is that hydrometers are like hand grenades and horseshoes. just need to be close but not spot on

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As long as it is off the same at multiple points and you read it the same everytime then you are going to get consistent results.

So we put a man on the Moon, have a rover on Mars, our phones can give us directions, and take great pictures. Why do we not have digital hydrometers?

CBXBob said:

So we put a man on the Moon, have a rover on Mars, our phones can give us directions, and take great pictures. Why do we not have digital hydrometers?

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Even if we did they'd probably be way too expensive. $5 for a glass one that may be a hair off is fine w me. If a company offered calibrated ones that were more expensive I'd pass cuz they break way too easily.

The difference between 1.056 and 1.055 isn't enough ti worry about. As long as readings are stable at the end of fermentation it's doing it's job for me.

from High School chemistry I've always measured to the center of the miniscus:



My hydros read right on at 1.000 - I will have to try them at known higher density and see if they drift. I'm more concerned about the lower gravity readings - I use a refractometer going into the fermenter, hydro later in the process.

passedpawn said:

I have 3 hydrometers. Here's my test data, all adjusted for 60F. Draw your own conclusions.

Refractometer: Water: 1.000 Test Solution: 1.100 (as much as I could discern the fine lines)
Hydro 1: Water: 1.000 Test Solution: 1.101
Hydro 2: Water: 1.002 Test Solution: 1.111
Hydro 3: Water: 1.000 Test Solution: 1.100
​

From our own wiki, these two conflicting entries:

https://www.homebrewtalk.com/wiki/index.php/Talk:Hydrometer

https://www.homebrewtalk.com/wiki/index.php/Hydrometer

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OK, so I just wanted to repeat something that kinda got buried earlier. Hydros can be way off. I have one that is quite bad. See the data below. Hydro #2 is off by 11 points at 1.100. Like the OP says, test your hydros.