Using A Hydrometer

The hydrometer is one of the home beer or winemakers most important  and frequently overlooked - tools. Many people find using a hydrometer too complicated. In reality, a hydrometer is a very simple device that measures the density of a liquid. In beer and wine making, the more unfermented sugar present, the higher the density.

During fermentation, the yeast converts sugar into alcohol. As sugar is converted, the density of the wine or beer decreases. Measuring sugar density with the hydrometer before, during and after fermentation will tell you several important things.

First, most beer and wine kit manufacturers provide both starting and finishing specific gravity (S.G.) levels for their products. (Specific gravity is the reading you get from a hydrometer.) If a kit states that the starting gravity should be in the 1.070 to 1.080 range, and you get a reading of 1.076, you know the ingredients are correctly mixed and the product purchased was in good condition. As we will see later, it's important to keep a record of the specific gravity at each stage of fermentation.

Second, by measuring specific gravity during fermentation you can see whether fermentation is proceeding normally. Kit manufacturers indicate how long it should take beer or wine to reach certain S.G. levels. Not reaching those levels within the guidelines could be an indication of problems, like temperature fluctuations, sluggish yeast activity, unsuitable conditions. Most problems are easily treatable, if detected in time by using a hydrometer.

Third, measuring the specific gravity at the end of fermentation is the only reliable way to determine that fermentation has, in fact finished. You must get readings within the manufacturer's range of final S.G. for three days in a row, with no visible signs of fermentation. Possible consequences of unfinished fermentation can extend from difficulty clearing the product and high residual sweetness from the unfermented sugar, to exploding bottles due to continuing fermentation in the sealed bottle. The hydrometer is an absolute necessity.

The hydrometer also lets you calculate the potential alcohol content of your beer or wine. Many hydrometers have a potential alcohol scale built in. Here's how to use it.

On Day 1, when you mix all ingredients, take a hydrometer reading and note the reading on the potential alcohol scale. For example, an English Bitter may have an S.G. of 1.045. On the P.A. scale, this reads as 5.8. The same beer may have a finishing gravity of 1.010. On the P.A. scale, that's 0.9. To estimate the potential alcohol content of the beer, simply subtract the final reading from the initial reading: 5.8-0.9 = 4.9% alcohol per volume. This is the potential alcohol, reached if all the sugar is converted into alcohol, which is not always the case. But the P.A. is reliable enough to use as a guide to the alcohol content of your bottled beer or wine.