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How to Test Alcohol Measurement at Home

The first question in any home-brewer’s mind is “Will I get a kick out of it?” “How much alcohol it has?”. It becomes difficult to invite people over to taste without a precise scientific answer to this question,. There are two methods of measurement of alcohol:

Direct method:

As the name suggests, ABV (alcohol % by volume) is the measurement of alcohol in the final product.

Brewing Refractometer
Brewing Refractometer
  1. The most widely used is the distillation method. Here we take a standard sample (say 250ml) and distil it. The distillation separates impurities (like residual sugar which can interfere with our readings). The clear distillate is measured both in volume and in density. A hydrometer or a pycnometer can be used for this. This is the method preferred by FSSAI, Excise and tax authorities. Because it is simple (high school chemistry laboratory) and conclusive.
  2. Ebulliometer: Some home-brewers don’t want to keep an illegal moonshine distillation apparatus at home. Hence, the next best option for them is Ebulliometer. All we need is a digital thermometer (accuracy 0.1OC or higher). Measure the difference in boiling point of wine (or beer) as compared to that of deionized water. Higher the alcohol content, lower the boiling point is. Use a degree ebulliometer reference table to compute the alcohol percentage.
  3. Surface tension: This is the simplest of all the test. The meter (called vinometer) is a simple cup (few ml in size) and a capillary tube attached to it. The capillary measureS the surface tension of the wine. It helps compute the alcohol content. Fill the cup with a teaspoon of the sample and allow a few drops to drip. Then flip it over and read it like the analog thermometer.

Please note that dissolved CO2 interferes with the reading. Hence, we can not use it for beers and sparkling wines. Also the surface tension method is indicative at best. We cannot use it to measure the alcohol levels. It is still popular, because it is easy and yet intriguing experiment.

Indirect Method

Indirect method: Here we measure the sugar levels (starting and final) and compute the total amount of theoretical alcohol produced when the yeast ferments the sugar. The two most reliable methods of sugar measurement are:

  1. Refractometer: In this case, we take a few drops of the fruit juice on the prism and measure the change in refractive index. In the eyepiece, we see a horizontal blue and white divider line cutting a vertical black axis. The value at the junction is the refractometer reading. Most devices are calibrated to give Brix% but some give specific gravity and potential alcohol as well. The relationship between the three are in the table.

Since it needs just 2 drops, this method is great for wine makers who want to choose the ripest fruit to pluck/ buy. Also beer brewers find it easy and fast to measure the mashing efficiency of the wort.

Measure Alcohol in Beer Wine and Alcohol at home
  1. Hydrometer: Take 250ml sample of the liquid in a measuring cylinder and drop the glass hydrometer in it. We can measure the change in density by the buoyancy of the glass bulb of the hydrometer. Please remember, the fragile hydrometers contain toxic lead. Therefore, they can break into glass shards. So, we should not leave them in the fermenter for long. The best option is to use a tall glass cylinder.
correctly reading hydrometer
correctly reading hydrometer

Where, OG: original specific gravity before fermentation (e.g.: 1.050), and FG: final specific gravity (say 1.010).The potential alcohol = 132.7*(1.050-1.010) or 5.31%

For the indirect method to be accurate:

  1. We need to make sure that there is no oxidation happening.
  2. We need access to the original gravity and final gravity of the brew/ wine (hydrometer or refractometer).
  3. If there is any sugar during fermentation (step feeding in case of wine, or adding honey in some beer recipes in the secondary or even priming sugar during carbonation of beers), their impact on Brix needs to be manually calculated.
  4. Dissolved CO2 will cling to the hydrometer and introduce errors. Hence, wait for a couple of minutes before taking down the reading.
  5. Always take the reading of the lower meniscus of the hydrometer.
  6. Allowing the tall glass (measurement cylinder) to overflow gets rid of the floating debris and surface bubbles which can introduce errors.

Brix = (((182.4601 * SG -775.6821) * SG +1262.7794) * SG -669.5622)

hydrometer brix to specific gravity table
hydrometer brix to specific gravity table

​​Please note that adding excessive sugar (wine) or malt (beer) will not produce a super alcoholic drink. Yeast have an alcohol tolerance level i.e. maximum % of alcohol they can ferment before they become dormant. Also beer yeast have an attenuation, which is maximum % of maltose it can ferment.

Estimating Original Gravity Points

Points are simply the fractional part of the potential – so an extract with a potential of 1.046 is simply 46 points (I have explained about extract potential in the 2nd point). So, for a recipe today we will have 2.6 lbs (which is 1.2 kg that we used) of Pilsner malt (1.037) and 2.6 lbs ( which is 1.2kg) of wheat malt ( 1.036 potential) would give us:

37 points * 2.6 lbs = 96.2 points
36 points * 2.6 lbs = 93.6 points

Total = 189.8 points.

The next step is to apply an “efficiency” factor to our process. The potentials given for the grain are the maximum possible amount you could draw from the grains if you crushed them under laboratory conditions with no losses. Real mashing processes and subsequent sparging, boiling, and transferring are not ideal – so a typical brewhouse has an efficiency number far less than 100%. The brewhouse efficiency number includes all of the losses in the system into the fermenter including mashing, lautering, boiling, trub loss, and transferring the finished wort to the fermenter. A typical brewhouse efficiency number for a home system is 70-75%. In this case we’ll use 72%

189.8 points * 72% efficiency = 136.6 points

Now we just divide by the “into fermenter” volume which in this case is 2.64 gallons( 10L ):

136.6 points / 2.64 gallons = 51.7 points/gal

And that is the original gravity estimate if we convert it back to specific gravity – 51.7 points gives us an OG of approximately 1.052

Often brewers refer to a malt’s “extract potential.” This is typically expressed as specific gravity that can be achieved with 1.00 pound (455 g) of malt mashed in 1.00 gallon (3.78 L) of water.

The following formula can be used to calculate extract potential:

Extract potential (S.G.) = 1 + (DBFG / 100) * 0.04621

The 0.4621 multiplier in the formula is the extract potential of sucrose (1.04621), against which all extract is measured. For example, our pilsner malt with an Extract Yield Dry Basis Fine Grind (DBFG) value of 80.5% results in a calculated extract potential of 1.0372.

And for our wheat malt with a DBFG value of 79% results in a calculated extract potential of 1.036. Extract yield information for the malt is provided by your malt supplier.

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Do check if refermentation has not happened. i.e. the sugar added to back-sweeten (at the time of bottling) has not been consumed by yeast.

Winemakers use Brix (% sugar in the solution) and beer brewers uses degree Plato (% of malt or solids in the wort). Since the formulae and treatment for the two scales is exactly the same. Textbooks use Brix and Plato interchangeably.
Some of the commercially marketed kombucha, fermented health drinks and probiotics contain alcohol over the permissible limits. As per FSSAI norms, food with more than 0.5% alcohol is governed by the excise norms of the state. Hence it is important to get the finished product tested for a potential violation.
Brewing and wine making is a science where people have dedicated their lifetime towards perfecting them. However, let me leave you with two food of thoughts.

  1. As per ISO 9000: Measurement is the key to standardization.
  2. Management Guru Drucker once quoted “You cannot manage what you cannot measure.”
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