Measuring alcohol in homemade wine
Measuring alcohol in homemade wine
short & simple summary on hydrometers, specific gravity and alcohol by volume
Most of the information in this posting has been collected from sources independent of this site and are not uniquely created by me. Therefore it will be made available to everyone.
The percentage of alcohol in homemade wine is measured indirectly. That is you measure the change in specific gravity from start to finish, and then convert that number to potential alcohol volume (multiply by 131).
A hydrometer measures the specific gravity of a liquid solution. In the case of winemaking, a hydrometer is used to measure must or wine density, which is increased by fermentable sugars and other must/wine substances. During fermentation, yeast breaks down the fermentable sugars, producing ethanol and carbon dioxide. As the sugars break down and are metabolized, the specific gravity decreases. The hydrometer is used to measure this density change.
HYDROMETER BASICS
Hydrometers are made of glass with a weight at the bottom and typically three scales of measurement along the sides of its long narrow stem. Make sure when you take the reading on the correct scale marked as Sp.Gr. I will not cover the other scales in this article.
When placed in liquid, the weighted end is submerged and the top floats above the liquid. Take the reading at the top of the liquid (surface tension will cause the liquid to climb the sides of the hydrometer slightly, creating a “meniscus” — use the reading at the bottom of the meniscus). The specific gravity readings usually range from 0.990–1.120. The specific gravity of pure water at 60 °F (15.5 °C) is 1.000, or 0 °Brix.
HOW TO USE IT
Readings should be done with a sample of the must or wine in a clear cylinder (hydrometers are often sold together with a 250ml cylinder or a protective case that can be used). This allows for an easy line of sight to get a measurement. Your sample may be collected from the fermenter using a clean, sanitized turkey baster or wine thief. Pour the sample into a cylinder. Gently place the hydrometer into the sample, making sure the hydrometer is floating and not sunk all the way to the bottom (if this happens, you need more liquid). If bubbles gather around the top sides of the hydrometer, give the hydrometer a spin or wait for the bubbles to dissipate as they will affect buoyancy. Then record the specific gravity on a notepad or piece of paper.
WHAT IT MEANS
Knowing the specific gravity (and therefore the sugar concentration) of your wine wine can be useful prior to, during, and after fermentation.
Before fermentation, this measurement gives a basis for predicting the amount of alcohol that may be produced during fermentation. During fermentation, measurements will show you how much of the sugar has been consumed by yeast — giving you an idea of how quickly fermentation is proceeding. The hydrometer may also indicate when you have reached your final specific gravity (1.000 or less) and it is time to rack the wine off the yeast and sediment.
With recorded specific gravity at the beginning and end of fermentation, you can use these numbers to determine the approximate percent alcohol in your wine. One of the more popular ones is subtracting the final gravity from the original gravity and multiplying by 131. For example, if the initial reading is 1.100 and the final gravity is 1.000, then 0.100 x 131 = 13.1% alcohol by volume (ABV).
Rule of thumb and guidelines:
one pound of sugar will raise the specific gravity approximately 35 points in one gallon of must
one pound of Honey will raise the specific gravity between 30 to 35 points in one gallon of must
approximately 7.4 specific gravity points correspond to 1% alcohol by volume. OG ≈ 1.0074. or 1.074 would be 10% ABV
approximately 100 grams of sugar in one gallon will raise the potential alcohol by volume (ABV) by 1% or specific gravity 7.4 points