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Measuring beer

There are more than one concept to take the measure of a beer. Hops influence the bitterness, malts determine the sweetness. Finally, the alcohol content provides one last dimension to the brew.

A lesson in hops and color


Who would have thought that something as subjective as 'bitterness' could be measured and quantified? But thanks to the ingenuity of brew chemists, that's just what has been done. 'Brew chemist'. How's that for a career idea to warm the heart of every college sophomore.

Hops are cone-like flowers which grow on vines in temperate regions of Europe and North America. At the base of the petals are lupulin glands that contain the oils that contribute to the brewer's art.

Historically, hops were used more as a preservative than a flavoring agent. With modern brewing technology, that's no longer necessary, but the flavoring aspect is still extremely important.

Bypassing a lot of complicated chemistry and math, hops are bitterness rated by a measurement called IBU, or International Bitterness Units. An important component of IBUs is a factor called AAU, or Alpha Acid Units. It's the alpha acids in hops that provides most of the bittering effect that helps balance the sweetness from the malt sugar used. Beta acids form only about 10% of the total.

When added at the beginning of the boiling process that is the initial phase of fermentation, the hops contribute more IBU than if added later. Knowing the IBU rating for a sample of hops allows home brewers to control, to some degree, the bitterness level of their output.

Calculations are now more or less standardized and ratings range from less than five for a weakly hopped brew, while an India pale ale or Barleywine can reach as high as 50 IBUs or more.

Though the numbers are standardized, the results are not. The largest factor that affects the final outcome is the boiling time. Boiling causes the hop oils to break down and combine with the wort (the malt sugar liquid used for fermentation), which partly determines the amount of bitterness of the final brew.

The second largest factor is the specific gravity (SG) of the wort. Hop utilization decreases as the SG of the wort rises, since the higher concentration of sugars - and thus the greater SG - leads to fewer alpha acids dissolving into the mixture.

Measures of IBUs and tables of the quantity of hops to add are typically on the package or in the brew kit sold by your vendor.


Most beers are made largely from pale malt and a large percentage of specialty brewers prefer the two-row barley malt variety. But other malts are sometimes used to control the color and tailor the taste of the final product.

Like coffee beans, malt is roasted to caramelize the sugars and increase sweetness and produce attractive darker colors. Also like coffee beans, roasts come in all degrees. Some produce only a slightly tanning effect, while others nearly burn the malt giving a very dark brown. Roasted malts are typically added in graded amounts to produce just the degree of browning desired, from amber to chocolate.

Beyond color, special malts - such as carapils - are sometimes used to mix in a larger amount of unfermentable sugars, producing a sweeter final brew. Unmalted barley is even used in some cases to increase head retention.

Malts, like hops, have now a standard rating, in this case the so-called 'Lovibond' scale. Using the Lovibond number can help a home brewer tailor his color, just as IBUs are useful for honing bitterness.

For example, ten pounds (4.5 kg) of 40L malt would produce the same color as 40 pounds (18.2 kg) of 10L malt. The normal range is from as low as about two for very light American beers, to around 40 for a good British stout.

Again, the package or home brew kit should provide the number, which you can use as a starting point for creating your own unique brew.

A lesson in calculating alcohol content

Half-pint, pint, liter, you say? When ordering one to drink, perhaps. But, when it comes to measuring beer, brewers have something else entirely in mind.

Specific Gravity

For reasons known only to history, the term 'specific gravity' refers to a liquid's density. By convention, pure water is assigned a specific gravity (SG) of 1.00 at 15.5C (60F) and is used as a standard. The 1.00 refers to the fact that the density of H2O, in metric units, is 1 kg/liter. So, if a liter of beer has an SG of 1.05 it will have a mass of 1.05 kg.

When used in brewing, specific gravity is broken down further into 'Starting' or 'Original' gravity (OG), which is a measure of SG before fermentation. The number helps brewers measure how much sugar is dissolved in the wort, the malty-liquid that is fermented to make beer.

Normal range for OG is from 1.020 to 1.160. Note that British charts often omit the decimal point. The added density is the consequence of sugars dissolved in the water, which will get converted to ethanol (the alcohol in beer) by fermentation.

Measurements are made of specific gravity after fermentation as well, where the number is called the 'Final' or 'Terminal' gravity (TG). The difference between the final number and the initial number provides a simplified method for estimating the amount of alcohol produced during fermentation. Fermentation converts maltose into ethanol and carbon dioxide, with most of the CO2 bubbling away during the process.

Since ethanol is less dense than the sugary water (wort) the Terminal Gravity is less than the Original Gravity. Pure ethanol has an SG of 0.79 kg/L. One side effect of this is that sweeter beers will have a lower OG, since the yeast doesn't completely convert all the malt sugar available in that case.

Here's a table with common ranges for different styles of beer:

Milds, Wheat Beers: 1.020-1.040 (OG)
Lagers, Stout, Porter, Pale Ale, Bitters: 1.040-1.050 (OG)
ESB, IPA, Oktoberfest: 1.050-1.060 (OG)
Strong Ales, Bocks: 1.060-1.075 (OG)
Barleywines, Belgian Trippels: > 1.075 (OG)

Alcohol Content

Calculating the amount of alcohol in the fermented brew is easy, with a little bit of help from simple chemistry. Skipping some technicalities, we find that the amount of CO2 produced for every gram of ethanol produced during fermentation is 1.05.

Suppose the OG is 1.06 and the TG 1.02. This means 0.04kg/L of CO2 has bubbled off. The alcohol content left behind is therefore:

1.05 x (1.06 – 1.02) = 0.042 kg/L. To calculate the percentage of alcohol is elementary from here. 0.042 / 1.02 = 0.041 or 4.1%.

This is the amount of alcohol by weight. The amount of alcohol by volume (the number you see quoted on cans and bottles) is a little larger. To convert one to the other is also easy. Just divide by the density of alcohol, 0.79 kg/L.

Alcohol by volume: 4.1% / 0.79 = 5.2%.

These simple guidelines can help home brewers estimate how much alcohol is produced during fermentation. Or, you could just use the old-fashioned method and drink.