I want to measure the sugar content of several brewed beers. What is the best equipment to use for this (e.g., Brix hydrometer) and how accurate would the result be using this technology?
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Unfortunately, you're not going to easily achieve the solution to your question. Your best bet would be to find the nutritional information for the beer you seek. It isn't readily available, though, legislation has passed requiring craft beer producers to provide this information. While this sounds logical - this can significantly impact smaller craft brewers. :(
You can't actually tell what the sugar content is of a beer without knowing the Final Gravity of the wort before fermentation giving you the Original Gravity. These difference in OG-FG tell you the Alcohol By Volume of the beer in question. Specific gravity is measured in kg/(m^3) - I'm sure there is some math that could be done to figure out how to convert a known Final Gravity into know sugar amounts.
- The downside becomes knowing what type of sugars were in the original recipe. Without knowing exactly what went into the beer (and recipes can be quite proprietary) - you'll be hard pressed to figure out exact sugar content.
I've been holding off answering this question because it's very complicated. First, I am assuming the original poster wants to know sugar content in finished beer, not in pre-fermented wort. If that is not the case, I will pull my answer.
In the wine industry it's pretty straight forward to measure residual sugar since all you are dealing with is leftover fructose from the unfermented portion of the wine. One sugar, easy. It's pretty accurate with a Clinitest (now Aimtabs).
But with beer, it's different story because you are dealing with several types of sugars and frankly brewers don't have the same problems with unfermented sugars that winemakers do. (This is how we have fizzy wine!) So, finding a test for residual sugar in beer is not only more complicated but rare.
You cannot use a refractometer or hydrometer to measure residual sugars directly since alcohol influences the end results. One method is to evaporate the alcohol content and then with the alcohol gone you could measure the sugars directly. This would have to be done with vacuum distillation so you don't lose the water content.
I did find an old paper from 1977 which describes several scientific methods but these are generally too hard for the average person to take on.
MEASUREMENT OF CARBOHYDRATES IN WORT AND BEER
By G. K. Buckee and R. Haroitt (Brewing Research Foundation, Nutfield, Redhill, Surrey) Received 20 May 1977
Methods are reviewed for measuring total wort and beer carbohydrate and carbohydrate fractions, such as dextrins, oligosaccharides, fermentable sugars, jS-glucans, total fructose and fructosans, pentose and pentosans. The methods are conveniently classified under the following headings: reductometry, colorimetry, enzymic procedures, automated analyses, paper and column chromatography, thin layer chromatography, gas liquid chromatography and high performance liquid chromatography. Techniques involving chromatography are particularly useful for separating and estimating individual sugars.
I found this device on Amazon - which I believe will do what you want.
Brix Refractometer Measure Sugar content for Beer Wine
It determines the sugar content not just in beers, but in wines as well (also fruits etc.).
What is a refractometer?
A refractometer is an optical device that, like a hydrometer, measures the specific gravity of your beer or wort. It does so by sampling a small amount of liquid, and looking at its optically. The main advantage over a hydrometer is the small sample size needed – typically only a few drops.
Most brewing refractometers measure samples in Brix, which is a scale used to measure specific gravity primarily by wine makers. Some also use a Refractive Index (RI) scale. Both the Brix and RI indexes need to be converted to standard specific gravity or Plato scales using a formula, as wort does not have the same reflective properties as plain sugar water.
Using Your Refractometer when Beer Brewing
Using the refractometer is very similar to what you just did when calibrating it. Open the sample plate, make sure it is clean and dry, then add a few drops of your wort. Again, if the wort is hot allow it to cool to room temperature first (ideally 68F). Close the sample plate, check for bubbles, and then hold the refractometer up to a natural light source.
Reading the refractometer is easy – just take the reading directly from the sight scale. The reading you take will most likely be in percent/degrees Brix or RI. - How to Use a Refractometer, Brix and Beer Brewing
You can measure it through distillation process, Take 100ml of beer and distill it approx 20-30 min at 85 degree Celsius. In this process the ENA will be collected separately and then the remaining content will be Sugar solution + other traces of Barley. Measure the brix of this solution, you will have your answer.!
Comparing the original gravity (OG) and final gravity (FG) will give you a sense of the calories left in a beer. There is an online calculator here: http://www.mrgoodbeer.com/carb-cal.shtml
This will not give you an accurate number for say labeling purpose, but it will get you in the ballpark. There are well-established tests that can determine caloric content in foods, but they require a lab and some knowledge.
Unfortunately, at home you won't be able to measure the alcohol content 100% correct, BUT there are devices available today that are going to give you pretty good estimation of alcohol content in your finished beer. Remember that after fermentation your beer contains alcohol which has lower density than water.
Hydrometer You can measure specific gravity of your wort and your finished beer using the hydrometer. There are calculators avaliable online to tell you how much alcohol your beer has. You just enter OG and FG into calculator and it will give you estimated ABV. There is no need to adjust for alcohol density using hydrometer.
Refractometer You can buy a refractometer and measure specific gravity (SG) of your wort pre and post fermentation. Pre-fermantation reading is going to be an accurate one (for example, if you see 1.050 then you write down 1.050). With refractometer you need to adjust for alcohol density. Or you can use an online calculator that does it for you: https://www.brewersfriend.com/refractometer-calculator/ You just enter OG and FG as you see it on your refractometer and it will give you Adjusted FG and estimated ABV.
Pycnometer This is the method I prefer (altough few people use it) because it is the most precise measurement tool that you can have at home. You need a pycnometer and an accurate scale (better accuracy, better measurements -> 0.1 gram accuracy should be more than enough). What you do is you calibrate your pycnometer. Fill it with distilled water at X Celsius (usually it is 20C but you can choose different temperature -> choose one that is close to your usual wort pitching temp) up to a marked level in the pycnometer and measure the weight. Then, at the same temperature you weight your wort which will allow you to determine the exact amount of sugar in the wort. You do the same with the fermented beer. After that you have your OG and FG estimated by pycnometer instead of refractometer and can use the same calculator for estimated ABV. Pycnometer is just more accurate then refractometer but requires more work.