Proper Gravity Testing Techniques?

Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum

Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

TronCarter

Well-Known Member
Joined
Sep 5, 2007
Messages
73
Reaction score
0
Location
Kalamazoo, MI
I am just getting into wine making and would like some advice on gravity testing. I see that hygrometers and refractometers are available but don't know which one to choose. If I get a hygrometer and test jar, what is the proper way to use it? What do you do with the test wine you removed from the carboy?

Any help is appreciated.

Tron
 
Hey Tron. The biggest issue is of cost. A decent hydrometer will run you about $12-$25 and a decent refractometer will be anywhere from $50 - $120 (the difference being temperature compensation) and up to $300 for the digital models.

The biggest difference is sample size, since you won't need to cool your must like brewers need to cool the wort. Basically, a hydrometer needs a sample sufficient to float in and a refractometer just needs a couple drops and a light source to look at. I have to say, after having done the wine thing for some time and now into the beer thing, the refractometer is much easier, but the potential for error in the sample selection is a lot higher since you're testing a much smaller sample. Refractometers also are calibrated to Brix, which would require conversion to SG - which is easy. The small sample size is much more useful for tracking fermentation progress, which is also a benefit for a long wine fermentation and tracking the proper time to rack into secondary.

Basically, refractometers are easier but require a little more attention to detail. If you've got the cash, get a refractometer and then get a cheap hydrometer for more precision in original gravity readings. If you don't have the cash, just get a high-quality triple scale hydrometer w/ thermemeter. It'll cost you about $25 and will last a lifetime if you don't drop it like I do all the time.
 
Since you are just getting started, get a hydrometer, a wine thief ,and a graduated cylinder.

its a cheaper investment that still gets you exactly what you need.
 
Ok, thank you for the advice. I would assume that the tested sample is discarded and not returned to the fermenter?
 
I was under the impression that without some sort of advanced formula you can not use a refractometer with fermenting or fermented wort. Ie. you would only use a refractometer for the SG.

Have I been misled?
 
Well, let me back up a little further. What else would I want to be testing besides SG? I want to know the SG so I can check progress or stop a batch at the proper SG. I also want to be able to calculate ABV. I actually own a refractometer for my saltwater aquariums and it should cover the range I need and it is already marked in SG and I won't have to convert from brax. It is even and automatic temperature compensated model, so I think I will try it out.

Also, anything removed with a wine thief could and should be consumed (if palatable) but I was more questioning the potential contamination of putting it back into the fermenter.
 
If you sanitize everything you can put it back in. With wine the ABV is damn high so you are safer then with beer. Or you can just drink it like I do. :D
 
I drink all my samples. The chances of contamination from the sample's contact with the test flask that you float the hydrometer is really really high unless you're diligent about sanitizing it. Also, particularly with wine, you can get pretty good at evaluating the progress of a fermentation by tasting the sample. Also - I'm usually just really curious about what the stuff tastes like.

As far as using a refractometer to measure SG, you just have to convert from "degrees balling" or Brix to SG. The easiest way is to look at a triple scale hydrometer. Its calibrated with SG and Brix and you can just read across the scales for a quick conversion. Also, you can Google hydrometers and get to these kinds of conversion tables.

http://www.ertco.com/hydrometer_conversion_tables.html

Now there's one other aspect that I forgot to mention. Hydrometers measure the density of a liquid in relation to the density of undiluted water. Refractometers are generally calibrated to measure relative concentrations of sucrose in a sample by measuring the deflection of light through the sample. This causes problems when trying to directly convert because 1.) the density of wort is effected by things other than sugar, and therefore hydrometer readings are always reflecting an artificially elevated sugar/particle content and 2.) wort contains maltose, not sucrose.

This first problem is really not that big a deal, and is apparently termed "Apparent extract v. Real extract", and is really a correction factor of only about 2-6%. Likewise the maltose conversion is a tiny number.

The upshot is that if you're looking for real precise SG readings, you're going to need to take both apparent-extract-corrected SG and Brix measurements and factor them together to get a true picture of the actual sugar content of the wort.

In the meantime, I'm not really that interested in getting that precise and although I've been taught how to do all that crap, I really am happy with a quick-and-dirty-and-get-back-to-my-RDWHAHB-pint once I figure I'm floating around the right ballpark. I tend to think the refractometer is a good tool because the sample is small and its a quick read for on-the-fly measurements and when to kill the boil, etc. but I generally rely on SG readings for comparing apples to apples when I calculate the alcohol content.

Sorry... long answer...
 
A Hygrometer is not the same device as a Hydrometer, fwiw. A Hygrometer measures Humidity and a Hydrometer measures the Specific Gravity of a liquid...i.e. it's density with respect to water which has a value of 1.000.
 
As Bobby_M pointed out the alcohol messes up the reading. Remember the refractometer is calibrated to read the change in refraction that sugar in a solution of water makes. After fermentation you have a solution of water + alcohol.

GT
 
Back
Top