Hops are the flowers of the hop plant (Humulus lupulus). The plant is a dioecious, climbing, herbaceous, perennial, usually trained to grow up strings in a field called a hopfield, hop garden or hop yard. There are many different varieties of hops around the world and production is concentrated in moist temperate climates. Hops are usually dried in an oast house before they are used in the brewing process.
They are used primarily as a flavouring and stability agent in beer, to which they impart bitter, zesty, or citric flavours; the plant part used in brewing beer is the hop flower, a delicate, pale green, papery cone full of perishable resins. Additionally, they are also used for different kind of purposes, like other beverages and herbal medicine. As a reward hops work as a preservative, and extend the life of beer.
In the past brewers flavoured their beer with a complex mixture called “gruit” that combined herbs and spices in recipes that varied from place to place.Nowadays when brewers add hops flavours and aromas, this are described appreciatively using terms which include “grassy”, “floral”, “citrus”, “spicy”, “lemony” and “earthy”.
In addition to water, cellulose, and various proteins, the chemical composition of hops consists of compounds important for imparting character to the beer. The composition of hop essential oils can differ a lot between varieties and between years in the same variety. About 250 components of essential oils have been identified and 22 of these are known to have a significant influence on the flavour and aroma of the beer.
These are some of the most important compounds:
- Alpha acids: Probably the most important chemical compound which are responsible for the bitter taste of beer.
- Beta acids: Hops contain beta acids which may be detrimental to the taste of beer. For this reason, beta acids are considered a negative factor in brewing and many brewers usually choose hops with a low beta acid content.
- Essential oils: The main components of hops essential oils are terpene hydrocarbons, responsible for the pungent smell of fresh hops and may give beer its prominent hop aroma and “nonbitter” flavour.
The effect of hops on the finished beer varies by type and use, though there are two main hop types: bittering and aroma.
- Bittering hops: have higher concentrations of alpha acids. These are boiled for a longer period of time, typically 60–90 minutes, to maximise the isomerization ( the molecule is transformed into another molecule) of the alpha acids. They often have inferior aromatic properties.
- Aroma hops: usually have a lower concentration of alpha acids and are the primary contributors of hop aroma. These are typically added to the wort later before it is cooled down to prevent the evaporation of the essential oils and then yeast is added, to start fermentation, a technique known as “dry hopping“.
The impact of a given amount of hops is specified in International Bitterness Units (IBUs), the measure of the concentration of hop compounds in beer. Beer lovers took pride in seeking out the brews with higher and higher IBUs.
Finally, beer wouldn’t be beer without hops. Hops provide the balance and are the
signature in many styles. The bitterness contributed by hops balances the
sweetness of the malt sugars and provides a refreshing finish.
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