![]() ![]() And, in order to do a two-point conversion, you need to be introduced to Plato - not the Greek philosopher, but a measure of extract weight frequently used by professional brewers.ĭegrees Plato (°Plato) is the percentage of sucrose (table sugar), by weight, dissolved in a water solution. ![]() To check to see if your hydrometer reads correctly in the range you use it in, you need to do a two-point calibration. However, what if the hydrometer read correctly at 1 but the scale printed on the paper sleeve inside the hydrometer was compressed or elongated compared to what it should be? A two-point calibrationĬhecking the reading of your hydrometer in pure water is a single point calibration, and this is all most homebrewers will ever do for their hydrometers. In other words, if your wort reads 1.050, your corrected reading would be 1.052. This means that it’s reading two “points” low and you should add two “points” from any reading you take in wort or beer. For example, let’s say your hydrometer reads 0.998 in pure water at 60 ☌ (its calibration temperature). If it reads either higher (1.001 or more) or lower (0.9999 or less), simply add or subtract the amount of error from your readings in wort or beer. If you’re lucky, your hydrometer reads 1.000 at the specified temperature. When reading your hydrometer, take your reading from the lowest point of the meniscus - the point where the liquid level intersects with the hydrometer scale gives you your reading. The curved surface of a liquid in a container is called a meniscus. However, it will climb up the sides of the test jar, making the liquid surface look like a “U” or smiley face. You will see that, in the middle of the test jar, the water will be level. Spin the hydrometer to dislodge any bubbles that may be clinging to it and bring the test jar up to eye level. So, to check if your hydrometer accurately measures the specific gravity of water, simply float it in pure water (distilled or reverse osmosis water) at the correct temperature. Tables that take temperature into account can be found in most beginning homebrew books. This temperature is almost always printed on the slip of paper inside the hydrometer. Because the density of water changes with temperature, hydrometers are meant to be used at a specific temperature (either 60 ☏/16 ☌ or 68 ☏/20 ☌). If your hydrometer is properly calibrated, it should read 1.000 when floating in pure water. For example, ale with an original specific gravity of 1.060 can be described as having 60 “gravity points.” A single-point calibration Since homebrewers almost always express specific gravity to three decimal places, many simply express their gravity in “gravity points” - the value of the last three decimals. In other words, the specific gravity of pure water is 1.000, not 1.000 followed by a weight and volume (such as kg/L or lbs./gallon). Because specific gravity is the density of a liquid relative to that of water, specific gravity has no units. Using that convention, the specific gravity of a liquid that was as dense as water would be 1.000. Homebrewers usually express specific gravity to three decimal places. Liquids that are equally as dense as water have a specific gravity of 1. ![]() (“Extract” here means dissolved solids, not malt extract - although malt extract may account for some of the total of your extract.) Homebrewers tend to express this in terms of specific gravity, which is the density of a liquid relative to pure water. When we use our hydrometers, we are measuring the density of extract in our wort or beer. Oddly enough, when you cool it below this temperature, it also expands. If you heat it above this temperature, it expands slightly. (In this column, I’ll mostly be using metric units and will only give conversions to English units if that knowledge is useful.)Īt 4 ☌, water is at its maximum density. Expressed in English units, the density of water is roughly 8 lbs. In other words, if you had exactly 1 L of water at 4 ☌ and placed it on a (properly calibrated) scale, it would weigh exactly 1 kg. Water has a density of one kilogram (kg) per liter (L) at 4 ☌. Density is the weight of an object divided by the volume it occupies. ![]()
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