Hops contain many biochemical compounds which partially defend the plant against all kinds of possible adverse environmental factors. These protective substances are concentrated in external organs, the lupulin glands, behind the bracts of the hop cone. Only the lupulin glands are of interest for beer production and for their health-giving properties. Each gland - a sort of little ball - is covered with a fine yellow resinous powder called lupulin. Lupulin powder contains, among other things, hop acids, essential hop oil and hop polyphenols. These constituents are present in varying concentrations in the different varieties of hop. Each hop variety therefore has its own intrinsic properties, which differ from all other hop varieties. The wholesale division of hops into bitter types and more scented types does not do sufficient justice to these finer characteristics.

Hop acids

A distinction is made between two related series of hop acids: alpha-hop acids, or humulones and beta-hop acids, or lupulons. The humulones have no direct application but, when hops are boiled with wort (a sugar solution obtained from the enzymatic decomposition of starch from malted barley or added grain), the humulones are converted into so-called isohumulones, which are present in all beers (from about 10 to 100 milligrammes per litre, sometimes more). These isohumulones give beer its typical characteristics. They are responsible for the bitter taste of beer, they are essential for the stability of the beer froth and they contribute to the shelf-life of beer by repelling Gram-positive bacteria. During the Middle Ages hops were used mainly to lengthen the storage life of beer rather than for their taste.

Beer must be stored in the dark. The influence of produces an unpleasant “light taste” (“cat’s piss”). Beer must therefore be stored in brown or green bottles and is best kept in a cellar. With today’s advanced hop products, developed in specialist laboratories for use in breweries, the influence of light is limited to a minimum or even completely avoided. High-technology hop products now allow the fine calibration of the bitterness of the end-product, improved foam stability and even storing beer in colourless bottles without the risk of producing the light taste.

Beta-hop acids, of lupulons, have a powerful antibacterial effect. They give Gram-positive micro-organisms little chance to multiply in beer. Derivatives of lupulons protect beer against oxidation.

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Essential hop oil

Essential hop oil - the volatile fraction of the hop - consists of more than 300 components. These include the so-called hydrocarbon-terpenes that give the hop its pleasant aroma. Humulene is one of the main terpenes in a high-grade hoppy aroma but, most of all, the interaction between the various aroma components is important. The essential hop oils are subdivided into a number of aromatic fractions with properties such as flowery, estery, citrussy and spicy.

A hoppy aroma is extremely important to appreciate the quality of the beer. Brewers traditionally use a bitter type of hop for the beginning of the wort-boiling to obtain the desired bitterness, then an aroma-type hop towards the end of the boiling process to bestow a hoppy aroma. To modify the beer flavour they may then add hop oil fractions obtained from hops via high-tech procedures. A brewer is thus able to modify the aroma of the beer any way he wishes.

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Hop polyphenols

There are at least 100 components in hop polyphenols. The properties of these substances are important for beer. Certain polyphenols protect the beer from oxidation, others are thought to be responsible for the cloudiness of the beer after long storage. Brewers are therefore not so happy about the presence of large quantities of polyphenols in their beer. Most polyphenols are therefore removed during the production process. This procedure guarantees a longer shelf-life.

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