Measuring Alcohol

How do I deal with measuring alcohol in my beer, wine, mead, etc.?

When measuring alcohol, using a hydrometer, take a Specific Gravity reading before adding yeast and just before bottling.  These are the two minimum times to take a readign to be able to calculate the alcohol content in your fermented beverage.

The hydrometer is used through out the fermentation to determine if sugar is being converted into alcohol. As more sugar is converted to alcohol the Specific Gravity will fall.

The Original Gravity (OG), the gravity just before adding the yeast, of a typical wine will be 1.075 to 1.090. Depending on the temperature and the activity of the yeast, this will change on a daily basis by about 10 points. After a few days the gravity will have typically dropped to 1.040. The Final Gravity (FG) of a wine will be in the region of 1.000 to 0.990.

How does the hydrometer work?

A hydrometer measures the amount of sugar in a liquid. The more sugar in the liquid, the higher the reading. As the sugars ferment and convert into alcohol, the reading gets lower. For example, if the hydrometer is placed in water at 20°C, it should read 1.000. This is always useful to know as you can test your hydrometer and make any necessary adjustments to your calculations.

How do I use a hydrometer?

A lot of people prefer to use a hydrometer with a trial jar. At Brew Craft, we carry a specific tool called The Thief which is used to collect the liquid. It is made of clear plastic and allows you to fill this with the liquid you are about to test. Fill The Thief and simply drop the hydrometer into the liquid.  After taking the SG reading, press the tip of The Thief against the side of your bucket or carboy to return the liquid to your batch.

As illustrated in the image below, you should take the reading from the lower of the two levels you see when looking at the side of The Thief. Be careful that the hydrometer does not stick to the side of The Thief, it’s best to give it a gentle spin to prevent this. If the wine is still bubbling then the reading will only be a guide (as there will be bubbles in the liquid) and if froth (in the case of beer) is present then gently blow this away.

Most people only use the hydrometer as a guide but if you want to be really accurate then this should be done with a liquid temperature of 20°C. If the liquid is 5°C higher then add 0.001 and similarly if its 5°C lower then subtract 0.001.

How do I use this to calculate ABV when measuring alcohol content?

The ABV can we worked out really simply by taking the OG from the FG and dividing this figure by 7.362. For example, the starting point for our wine is 1.080 and this ferments down to 0.990. The drop is 90 points. This divided by 7.362 is 12.23% ABV.

What should my OG be?

For wine, Original Gravity should be 1.070 (normal finished ABV will be 10.5%) to 1.090 (normal finished ABV will be 13%). Final Gravity should be 0.990 (for dry wines) to 1.005 (for sweet wines).

We recommend wine being fermented down to dryness (below 1.000). If you prefer a sweeter wine, then add sugar or grape juice at the end to reach your preference in sweetness. It is a dangerous business stopping the fermentation early.

For beer, this is very difficult to guide as there are so many variations and styles of beer. A typical beer will start at 1.045 and finish at 1.012 giving a 32 point drop (divided by 7.362) making it 4.5%ABV.

The hydrometer is probably the most essential piece of equipment to make wine and beer consistently and with success.

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