reading a hydrometer and hydrometer vs. refractometer

I have recently read we should read from the highest water line. Totally not what I have been doing for the longest time.

Also wonder what is there pros and cons using a refractometer vs. a hydrometer?

thanks

 

A hydrometer should be read according to the manufacturers directions. Some instruct that it be it be read at the base, some at the top of the liquid run up on the stem.

A refractometer is a sometime thing. It is certainly easier to use and faster, you are less likely to drop it and it is a snap to clean. But it doesn't always agree with a hydrometer. If you are thinking of transitioning to a refractometer you should make many comparative readings between refractometer and hydrometer to determine the conditions under which the agreement is acceptable to you (and acceptability is an individual determination).

 

I calibrated my hydrometers using known percents of sugar in water, and carefully created a calibration curve for each one. After using it a couple times I realized that reading at the top of the meniscus instead of the bottom as instructed by the manufacturer was the same as using the curve, for one of my 2 hydrometers. This won't work for yours, but the point I am trying to make is regardless of the manufacturer's instructions, calibrating your hydrometer is a good idea.

I did the same with my refractometer and happily it was right on from 0 to 20 B.

 

Really? That obviously impairs accuracy, and from what I remember from chemistry class, is wholly non-standard. 100 ml measuring glasses for instance, are always calibrated to be read from the water surface base.

 

My Hydrometer directions say read from the upper Meniscus. It's from France. Since I'm making beer for my personal enjoyment I'm not too worried if it's upper or lower as long as I read it consistently.

 

Hydrometers that are read from the top of the meniscus are usually for specialist fluids of known and constant surface tension, such as milk; fluids in which you cannot reliably see the baseline through the fluid. Okay, I suppose, as long as the surface tension of the fluids are comparable.

 

Or wort. Follow the manufacturers directions.

Also - making accurate sucrose solutions for calibration purposes is not so simple as it might at first seem. Tare a volumetric flask, add 1 gram of sugar, add enough water to make up to 10 grams, stopper and agitate. That will get you close to 10 °P but not spot on. To get spot on you would have to have lab grade sucrose, dry it in an oven, cool it in a dessicator and weigh it out somewhere other than Northern Virginia (where I live - the humidity is terrible). What I do is skip the oven and dessicator and make a solution of approximately 10 °P whose density I check with a more accurate instrument. Anyway, the "sensititivity" of a hydrometer (change in amount of stem out of the liquid per unit change of density) is wholly determined by the weight and geometry of the instrument so all you really need to do is check the 0 in distilled water. Note that the instrument will not read 0 in distilled water if it is calibrated for beer as the best brewers hydrometers are. This is that surface tension thing again.

Finally, a refractometer calibrated against sucrose solutions of known strength is great for measuring sucrose solutions (that what they are sold for) and will give an approximate reading in wort most of the time. But I've seen them read off by as much as 1 °P (1 Bx which, by the way, now a deprecated unit) in wort and of course as we all know they are way off in beer (i.e. once alcohol becomes a factor).

 

Sounds like a lot of fuss for .001 accuracy in you measurements. I'd be willing to bet that actual wort temp vs. calibrated liquid temp of the hydrometer would throw your accuracy off more than the point on the meniscus at which you read. I just do it the same and call that good.

 

aj,

Based on your knowledge and approach to these questions, I have to believe you were trained as a physical chemist. I am a simple synthetic organic chemist (i.e. a cook) and the way you poop out clear, correct and scientifically sound answers to all manner of questions here constantly impresses me.

I will continue to toss out my half-arsed answers to questions here, waiting eagerly for you to gently fill in the blanks, nudge me off the guardrails of chemistry, and complete the answer.

To illustrate, I did my calibration solutions on a lab balance I bought off eBay, good to 0.1 gram, calibrated with a set of weights from the lab at work, didn't bother to dry the sugar, and was happy to have made close enough calibration solutions that showed good agreement between my two hydrometers and one LHBS-sourced refractometer. I used RO water because I had some, to check 0 and since have found that my tap water is close enough to keep me happy.

Good enough for this old cook...

 

Certainly for the majority of home brewers 0.001 accuracy is more than enough but some of us are the geeky types. We own narrow range hydrometer sets that are easily read to 0.1 °P and with a little care to 0.05 °P which corresponds to 0.0002 SG. The lowest range member of the set starts at 0 °P and can, thus, be calibrated with DI water. The others do not start at 0 and thus must be calibrated against something other than water. I'm just pointing out that it is difficult to control the strength of a sucrose solution to 0.05 °P and that the only practical way to check such hydrometers is with solutions of approximately known strength against a more accurate means of measurement such as pycnometry or U-tube densitometry. The former is feasible for a home brewer who is interested in this (i.e. the lab/science) aspect of brewing. The latter isn't unless you have access to a brewery or distillery lab with the instrument.

 

I'm not a chemist - but do pretend to be one when I use hydrometers and refractometers.

I have used a hydrometer since I started brewing and to me, the difference between the top and bottom of the meniscus probably something less than my eyes can make out unless I bother to put my glasses on.

Getting back to your original question - I just bought a refractometer a few weeks ago and have done 4 brew sessions with it. It is very handy during the mash and boil. I found myself taking readings of first runnings last runnings, pre boil during the boil etc. The abilty to take a reading without having to worry about temperature and only using a drop or two of wort is very handy indeed.

The refractometer is best used before there is alcohol involved. Once gravity has started to drop (you've made some alcohol, you have to use a calculator to correct the reading. The same 4 batches of beer are fermenting right now and I learned the stupid way that the refractometer reading has to go through a correction process once sugar has been converted to alcohol (remember when I said I'm not a chemist?). The advantage during fermentation is that you only sacrifice a few drops of beer for gravity sample instead of a cup or so to get your hydrometer floating. There is also much less sanitizing involved - only the tip of the dropper touches the beer.

I tested all for batches with hydrometer and used refractometer and the brewmate correction calculator and they all came out the same.

For me, unless there is some compelling reason to use the hydrometer, it will probably stay in it's jar from now on. I love my refractometer.

 

The only reason I go to the hydro after fermentation is that I'm already itching to taste a few ounces to the sample is far from wasted.

 

I was trained as an electrical engineer but electrical engineers do lots of measurements too and the theory of measurement is the same whether it be the gain of an antenna or the temperature of beer in the fermentor.

As noted in my previous post much of what I throw out is moot because homebrewers, by and large, don't care or don't have the resources or time to worry about such arcana but I find this subject interesting, feel the world would be a better place if people knew how to deal with measurement better than they do. I hope some readers at least find this stuff interesting.