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Hydrometer Basics For Home Brewing And Wine Making

The Hydrometer

The hydrometer has been specifically designed for the wine and beer maker. It covers a relatively broad range, and therefore, eliminates the need for several instruments of narrower ranges to get the job done.

A hydrometer is an instrument for measuring the density of a liquid in relation to water. Water is given the arbitrary figure of 1.000, and other liquids are compared to this figure. The result is said to be their specific gravity (often abbreviated to SG).

As you add sugar, malt extract, honey, or other soluble solids, the numbers after the decimal point increase. As the beverage ferments, the sugars are converted into carbon dioxide and alcohol which is lighter than water so the specific gravity number decreases.

Determining Alcohol Content

Hydrometers have many uses, but the most common use by wine, beer, and mead makers is determining the alcohol content of a homemade beverage. This is quite simple, actually.

Step 1:Take Reading Prior to Fermentation

It is impossible to accurately determine the alcohol content of a fermented beverage without this initial reading. Your hydrometer should have a scale called the potential alcohol (PA) scale. This scale measures the amount of alcohol that will be potentially produced if fermented to dryness (SG of 1.000 or less).

The easiest way to take a reading is to sanitize a wine thief or "gravy baster", then remove a sample of the must or wort and place this in the test stand (this can even be the plastic tube the hydrometer comes packed in). Fill the stand about 3/4 full, then carefully place the hydrometer in it.

Give the hydrometer a gentle spin with your thumb and middle finger. This should remove any air bubbles that might otherwise cling to the sides of the instrument. When the hydrometer has settled, take the SG (and/or potential alcohol) reading with your eye at the surface level of the liquid. Read the scale inside the instrument at the level where the liquid contacts the glass.

Step 2: After Fermentation Is Complete, Take Another Reading

Subtract the potential alcohol reading at this point from the potential alcohol reading prior to fermentation. The difference between the two numbers is the alcohol content that you have actually produced.

For example: if the initial reading is 13% and the final reading is 1%, then the actual alcohol content is 12% (or 13% - 1% = 12%).

Please note that if your beverage ferments completely dry (SG of 1.000 or less), then the alcohol content is the same as your original potential alcohol reading (in the above example: 13% - 0% = 13%). The reason that the final gravity might end up lower than water is that you are producing alcohol, which is noticeably lighter (less dense) than water.

All dry wines and meads will finish at gravities lower than 1.000 (e.g. .995). Almost all beers and sweeter wines & meads will finish higher than 1.000.

Uses For Wine Makers

The hydrometer can be used to determine the natural sugar content of the must.

In most instances additional sugar should be added to the must to assure that the alcohol content of the finished wine is sufficient for the wine to keep. Alcohol is a preservative, and you should ensure that your wine has an alcohol content of at least 9 - 10%. Lower strength wines will be susceptible to spoilage.

By determining the natural sugar content you can then adjust the sugar content to the desired SG reading. In many cases a SG of 1.090 is desired to begin the must, as this gives a potential alcohol by volume of 12%.

Hydrometer Procedure For Wine Makers

Step 1:

After sanitizing a wine thief or gravy baster, remove a sample of the must and place it in the test stand. Take a reading, then refer to the hydrometer chart below. This will indicate the natural sugar content in the must.

Step 2:

To determine how much additional sugar is necessary to bring the must to the desired SG (let's say 1.090), use the chart below. For example: If the initial gravity reading is 1.040, then each gallon of juice contains the equivalent of 1 pound, 1 ounce of natural sugar content. If you consult the chart, at the desired level of 1.090 (12% alcohol), the sugar content should be 2 pounds, 6 ounces. Now do the arithmetic.

At the desired original gravity (OG) of 1.090, there is 2 pounds, 6 ounces of sugar per gallon
At the initial original gravity (OG) of 1.040, there is: - 1 pound, 1 ounce of sugar per gallon
The difference or sugar to be added is: 1 pound, 5 ounces of sugar per gallon

By subtracting the two sugar contents, you determine how much additional sugar should be added per gallon. It is not necessary (but still not a bad idea), to dissolve the sugar in some boiling water before mixing into the must.

Step 3:
Note that as a general rule of thumb, 1 pound of sugar dissolved in 5 gallons of must will raise the potential alcohol content by approximately 1%. Therefore, if you check the gravity of the must and it reads a potential of 9%, and you wish to produce 12%, simply add 3 pounds sugar. Note that this is for 5-gallon recipes.

Hydrometer Chart

Specific Gravity (SG)

Potential Alcohol (PA) % by Volume

Amount of Sugar Per Gallon

1.010

0.9

0 lbs. 2 oz.

1.015

1.6

0 lbs. 4 oz.

1.020

2.3

0 lbs. 7 oz.

1.025

3.0

0 lbs. 9 oz.

1.030

3.7

0 lbs. 12 oz.

1.035

4.4

0 lbs. 15 oz.

1.040

5.1

1 lb. 1 oz.

1.045

5.8

1 lb. 3 oz.

1.050

6.5

1 lb. 5 oz.

1.055

7.2

1 lb. 7 oz.

1.060

7.8

1 lb. 9 oz.

1.065

8.6

1 lb. 11 oz.

1.070

9.2

1 lb. 13 oz.

1.075

9.9

1 lb. 15 oz.

1.080

10.6

2 lbs. 1 oz.

1.085

11.3

2 lbs. 4 oz.

1.090

12.0

2 lbs. 6 oz.

1.095

12.7

2 lbs. 8 oz.

1.100

13.4

2 lbs. 10 oz.

1.105

14.1

2 lbs. 12 oz.

1.110

14.9

2 lbs. 14 oz.

1.115

15.6

3 lbs. 0 oz.

1.120

16.3

3 lbs. 2 oz.

1.125

17.0

3 lbs. 4 oz.

1.130

17.7

3 lbs. 6 oz.

 

Correcting For Sample Temperature Deviations

Most hydrometers are calibrated at 60 degrees F, and sample temperatures higher or lower than this need to be corrected. Consult the accompanying correction chart to determine the amount of the adjustment. For example: if your sample reads 1.045, but it is at 84 degrees F, then you need to add .003 for an adjusted reading of 1.048.

Temperature Correction Chart

 Temperature
of Sample (degrees F)

Specific Gravity (SG) Reading
Correction

50

-.0005

60

.000

70

+.001

77

+.002

84

+.003

95

+.005

105

+.007