Copied with permission from https://www.arishtam.com/product-page/aristam-homebrewing-guide and https://www.amazon.in/Arishtam-HomeBrew-Probiotics-Indias-homebrew-ebook/dp/B07WSXSCQY
The first question in any home-brewer’s mind is “Will I get a kick out of it?” “How much alcohol it has?” Without a precise scientific answer to this question, it becomes difficult to invite people over to taste. 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.
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. This can be done either with a hydrometer or by pycnometer. This is the method preferred by FSSAI, Excise and tax authorities because it is simple (high school chemistry laboratory) and conclusive.
Ebulliometer: Some home-brewers don’t want to keep an illegal moonshine distillation apparatus at home. Hence, the next best option for them is Ebulliometery. 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.
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 measure the surface tension of the wine and that is used to compute the alcohol content. Fill the cup with a teaspoon of the sample, allow a few drops to drip and then flip it over and read it like the analog thermometer.
Please note that dissolved CO2 interferes with the reading. Hence, it is not used for beers and sparkling wines. Also the surface tension method is indicative at best and cannot be used to measure conclusively the alcohol levels. It is still popular, because it is easy and yet intriguing experiment.
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:
Reading: 15 BRIX and 1.065 specific gravity)
Refractometer: Here 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.
Hydrometer: Take 250ml sample of the liquid in a measurement cylinder and drop the glass hydrometer in it. The change in density is measured by the buoyancy of the glass bulb of the hydrometer. Please remember that the fragile hydrometers are made of toxic lead and can break into glass shards. Hence don’t leave them in the fermenter for long. The best option is to use a tall glass cylinder.
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:
We need to make sure that oxidation has not happened (i.e. sugar is converted to alcohol and not acetic acid).
We need access to the original gravity and final gravity of the brew/ wine (hydrometer or refractometer).
If 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.
Dissolved CO2 will cling to the hydrometer and introduce errors. Hence wait for a couple of minutes before taking down the reading.
Always take the reading of the lower meniscus of the hydrometer.
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)
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.
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 commercially marketed kombucha, fermented health drinks and probiotics have been found to 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.
As per ISO 9000: Measurement is the key to standardization.
Management Guru Drucker once quoted “You cannot manage what you cannot measure.”