How to Read a Hydrometer When Making Wine

Most hydrometers come with three units of measure, all indicated by a single reading.

One of the most common tools used in beer and wine-making is the hydrometer. The hydrometer is a measuring device that is suspended in a sample of wine to measure the "gravity"--or weight--of the wine as compared to water. This tells how the fermentation is proceeding and the current strength of the wine. Most hydrometers come with two or three measurements, most commonly the SP.GR (specific gravity range) and the potential alcohol by volume scale. Some hydrometers also come with a Balling scale, which measures the sugar percentage of the fermenting wine.

Things You'll Need

• Wine
• Hydrometer
• Hydrometer sample tube
• Brewing sanitizer
• Pen and paper
• Logbook

Instructions

Reading the Specific Gravity Scale

1. Measure your wine's SP.GR by free floating the hydrometer in a sample tube and reading the numbers that appear just above the center of the wine level.

2. Calculate the weight of your wine as it compares to water. The SP.GR of water is 1.000, so your fermenting wine is measured in relation to that. This measurement will change over time, giving you a final reading.

3. Record your starting SP.GR and repeat the measuring process throughout fermentation. SP.GR is measured starting one space past the decimal point. So if a wine starts at 1.080 and ends at 1.010, it has lost 90 percent of its volume, and therefore has an alcohol percentage of 9 percent.

Reading the Potential Alcohol by Volume Scale

1. Compare your SP.GR reading to the potential alcohol by volume (PAV) scale on the other side of the hydrometer. Your initial measurement of 1.080 SP.GR indicated a PAV of just more than 10 percent.

2. Rerecord your PAV each time you remeasure your fermenting wine. Just as with the SP.GR scale, the amount by which the measurement goes down in the percentage of alcohol in the final product.

3. Aim to have a final alcohol percentage above 10 percent, as this is the minimum needed to properly preserve wine. A batch that has an initial PAV reading lower than 5 percent will need to have additional sugar added.

Reading the Balling Scale

1. Calculate the percentage of sugar in your fermenting wine by using the Balling scale on your hydrometer. This is a simple percentage scale, with the number floating at the surface directly translating into sugar percentage.

2. Use the Balling scale to adjust the sugar percentage of your wine as needed. Pure water will read at 0 percent sugar, while wine will need sugar to create alcohol. Additional sugar can be added if the Balling scale, SP.GR and PAV all read to low.

3. Compare your Balling scale to your PAV and SP.GR scales by simply rotating the hydrometer in the sample tube. Recording these comparisons before fermentation will be a great guide for tweaking recipes in the future.

Tips & Warnings

• Repeat your measurements as the fermentation process continues. This will both educate you about the process, as well as tell you when fermentation is complete.

• Draw your sample of the wine using a pair of sanitized tongs wrapped around the sample tube, a sanitized "wine thief" or even a turkey baster. You'll want the tube full about two-thirds of the way, leaving room for the hydrometer to float.

• Most hydrometers are calibrated for 60 degrees Fahrenheit. Measurement made outside this temperature will have to be adjusted up or down by 0.001 SP.GR per seven degrees.

• Carefully sanitize the hydrometer and the hydrometer testing tube. Make sure you use brewing sanitizer that will not pollute your fermenting wine.

• Make sure your hydrometer is floating freely and not touching the sides of the sample tube.

References

• Grapestompers: How To Use A Hydrometer in Winemaking
• Winemaking: Using Your Hydrometer
• Fermentarium: How to Read a Hydrometer

Resources

• Fermentation Trap: Testing Supplies