Buying guide for best hydrometers
If you make beer, wine, hard cider, mead, spirits, or liquor at home, a good hydrometer is essential. Professional brewers wouldn't be without one. While some people assume that it is just for checking alcohol content, a hydrometer is also invaluable for assessing yeast fermentation, measuring the sugar content of must (skin and pulp) when making wine, and telling you when the brewing process has finished. Without a hydrometer, you’re just guessing, and it's virtually impossible to produce consistent quality.
The hydrometer is a relatively simple instrument, but there are various models on the market, and that can make choosing the right one difficult. BestReviews has been busy researching what's available and assessing your options. We've made some recommendations that represent a a good cross section of the hydrometers for sale, and we've assembled the following hydrometer buying guide to focus on the the details.
If you’re ready to buy, check out our top picks in the matrix above.
Key considerations
Components
A hydrometer is composed of a thin glass tube with one or more scales marked on a plastic or paper insert. Below that is a larger bulb for buoyancy. At the bottom is a weighted plug, usually containing steel balls, to balance and calibrate the instrument. In the past, the plug was filled with lead or mercury, but both of these metals are extremely harmful, and in the event of a breakage could get in your brew! We haven't come across any hydrometers that still contain lead or mercury, but do check that your instrument is nontoxic.
Along with your hydrometer you need a testing tube, jar, or other vessel to hold the liquid to be measured. Many hydrometers require a minimum of 250 milliliters (ml), though some come with their own tube that only requires 125 ml. Because you should never return the sample to your brew, the latter reduces the amount of brew you waste.
Glass is preferred for its clarity. Plastic has a tendency to fog or distort. Also, while some manufacturers supply graduated jars, an unmarked one makes it easier to see the hydrometer readings. Tubes are often quite slender and easy to knock over. Some come with a plastic “bumper” ring to help protect them if this happens.
Case and care
Cheap hydrometers can be very fragile and don't usually have a case. A hard case or padded box is a definite bonus. A cleaning cloth and brush are nice extras, too.
Certification
The National Institute of Standards and Technology (NIST) traceability/certification is a guarantee that the hydrometer was made to the same standard as a reference product that's known to be accurate, so the certified instrument has the same level of accuracy.
Digital hydrometers
A few digital WiFi hydrometers are now available. Most are designed to be used as an integral part of the brewing equipment and stay in situ during the whole process. These relay information wirelessly to a smartphone, tablet, or via a website. They deliver detailed information to wherever you happen to be, whenever you like. However, these are expensive and so will probably only appeal to serious enthusiasts or professionals.
Common hydrometer terms
ABV: Alcohol by volume; the percentage of alcohol in a given liquid.
Specific gravity scale: Standard marking system for all hydrometers; used to measure not just alcohol but also properties of all kinds of liquids, from milk to gasoline.
Brix/balling scale: Indicates sugar content of a solution; used particularly in winemaking.
Tralles scale: Also known as “Proof and Tralles”; often marked on hydrometer as simply “potential alcohol”; used to estimate alcohol content/ABV. A useful guide, but not completely accurate because it makes certain generalizations about the process. Precise calculations of alcohol content can only be made once fermentation is finished.
Triple scale: All three scales provided on the same hydrometer; the most popular model.
Borosilicate glass: Contains boron trioxide and silica; stable and resists thermal shock (far less likely to crack when heated or cooled than ordinary glass).
Hydrometer prices
You can find hydrometers that offer a reasonable degree of accuracy for $5 or $6, but these tend to be fragile. You really need some kind of case to protect them. Hydrometers with cases start at around $10 to $15.
For about $30, you can get a nice boxed set with hydrometer, glass sample jar or test tube, cleaning brush, and cloth. True scientific precision hydrometers – which only have a single scale – start at around $40.
There's quite a jump to digital hydrometers, with those currently available costing between $100 and $150 or requiring a monthly subscription.
Tips
Hydrometers are calibrated for use at a precise temperature, normally either 60°F or 70°F, which should be noted in the leaflet that comes with your instrument. If your sample isn't exactly at that temperature, the reading will be slightly off and you'll need to use a correction chart and some quick math to get the proper value. Many hydrometers include a chart, or you can find them online on brewing and winemaking websites.
Tiny air bubbles can attach to your hydrometer when you put it into your brew. This will give a false reading. Giving the hydrometer a quick spin will release the bubbles.
A hygrometer must be floating freely to provide an accurate reading, so make sure your sample vessel is large enough so the instrument doesn't touch the sides and deep enough so it doesn't touch the bottom.
It's tempting to check your brew regularly, but every time you open your equipment to take a sample, you risk letting in airborne bacteria or fungi that are especially attracted to the fermenting liquid. Depending on what you're making, there will be specific times when a measurement is necessary. Stick to proven guidelines to minimize any potential problems.
FAQ
Q. How do I know if my hydrometer is accurate?
A. You can test it using distilled water. It should read 1.000. If it's under, you can apply tape to the top. If it's over, some experts recommend filing away some of the glass. However, there's considerable risk of damaging your instrument. It might be safer to note the error and include it in any calculations.
Q. What exactly is specific gravity?
A. Strictly speaking, it's the ratio of the density of a substance when compared to a standard. It can be used for liquids, gases, or solids. For brewers and winemakers, it's the ratio when compared to water. You can use specific gravity to calculate the percentage of alcohol content (ABV) by measuring before fermentation (original gravity) and after fermentation (final gravity). ABV = OG - FG ÷ .00753. It's not scientifically precise, but it’s close enough for home brewers.
Q. Do I need a different hydrometer for distilling spirits?
A. You can use a beer/wine hydrometer for the initial mash, but you need a separate Proof and Tralles hydrometer (also called a proofing or spirit hydrometer or alcoholometer) for assessing alcohol content after distilling. Standard triple scale hydrometers tend to read to about 35% alcohol, often not high enough for spirits and liquors. However, the larger scale makes them less accurate than required for brewing or winemaking, so the two are not interchangeable.
