Although it might look like a prop from the popular, campy science-fiction show Dr. Who, a refractometer is actually a marvelously handy tool; most commonly associated with brewing and winemaking, it has uses that can extend across the productive homestead.
Just like the more common hydrometer, a refractometer measures the sugar content of a liquid (wort for a beer, must for a wine, et cetera). It works completely differently, however: Rather than observing a calibrated float bob in a vial of liquid, you put a mere drop or two on the refractometer’s glass screen, peer through the eyepiece, and read the results off the scale inside. The science at work relies on the index of refraction—the degree at which light bends when passing through different materials—and how it changes in the presence of sugar. It’s fairly heady stuff, but fortunately today’s refractometers have built-in scales and temperature compensation that makes using one a snap.
Why a Refractometer?
Functionally, a refractometer does the exact same thing as its cheaper compatriot, the hydrometer. Moreover, conventional wisdom says that you can’t use a refractometer to measure the sugar content of a liquid that also contains alcohol such as beer or finished wine (but more on that later). So why keep a refractometer around, then? Is it just for the gadget factor, the mad scientist cachet? No, there is one absolutely spectacular reason for using a refractometer: speed.
When testing your wort with a refractometer, all you need is a single drop and you have your measurement in seconds, making it possible to measure in “real time.” A refractometer makes the idea of in-the-field measurements of grapes or berries possible, as well as prevents squandering your valuable fermented beverage.
While a hydrometer is great for measuring starting and finishing gravities and figuring out final alcohol content, it offers no utility for on-the-fly adaptation. It’s a bit like cooking without ever tasting as you go, following a recipe but never checking doneness, texture, flavor, seasoning, or aroma, and waiting until your guests sit down to eat to find out how things turned out. The responsiveness and convenience of a refractometer means you suddenly can adjust things as you go and test things you never could before. For the homebrewer or winemaker, opens up these dynamic adjustments:
- Stopping your sparge at the desired sugar content rather than just using a fixed amount of water (this is what professional breweries do)
- Adjusting your process based on actual wort extraction (shorten boil times if extraction is low, extend them if it is long) and stopping your boil at the desired specific gravity rather than just relying on timing
- Modifying hop additions to match the actual gravity of the beer
- Harvesting fruit (grapes, berries, et cetera) at a desired level of sugar content (again, this is what goes on at the professional scale)
- Adding sugar to wine must to yield a specific Brix value
Many Homestead Uses
The uses of a refractometer go beyond various forms of alcohol production. Pick it up any time there’s a need to measure the sugar content of a liquid. Depending on your homestead, that might include testing the moisture content of honey from your hives, the quality of milk from your dairy animals, the ripeness of your orchard fruit, the sugar content of your maple syrup flow, or even the consistency of your tomato sauce. The results can be increased consistency, quality and marketability.
A Slight Limitation
As I mentioned above, you’re unable to use a refractometer to measure the sugar content of alcoholic products. This is because alcohol also changes the liquid’s index of refraction, confounding measurement. There are a few online calculators, however, that let you “back out” this factor if you know the liquid’s approximate alcohol content. The math involved is pretty subtle, however, and I wouldn’t regard the results as anything more accurate than an approximation.
When shopping for a refractometer, look for two things: automatic temperature compensation (usually abbreviated “ATC”) and a dual-reading scale with markings both for specific gravity (favored by homebrewers) and Brix (favored by winemakers and essentially interchangeable with the Plato scale used by professional brewers). ATC means you can use the instrument in the kitchen next to your stove or in the field on a frosty morning with equal confidence. Unless you work strictly with Brix or Plato, the few bucks extra that you’ll pay for a dual-reading scale is worth the convenience. For the homesteader, there’s no need to invest in a super-precise electronic refractometer: The common handheld “scope” is fast enough and accurate enough, and it’s a heck of a lot more fun to use!