'Humulus Lupulus'

The hop is a tall, climbing plant, related to the cannabis family, which includes hemp and nettles. It can grow as high as thirty feet, but is normally cultivated to 15-18 feet high bines (5 metres). Its roots dig their way down into the soil as far as twelve feet. A new hop plant takes about three years to get established, but will live for anywhere between ten and twenty years.

Hops are dioecious, which means that male and female flowers occur on separate bushes - hop farmers grow male hops to the windward side of their hop gardens, to facilitate fertilisation of the female hop flowers. It is the female hop cone, or 'burr', which is used in brewing.

The hops come into flower in July, and are harvested in September, when the bines are cut to about three feet above the ground. After the harvest, the hop plants are cut back to their roots, which remain in the ground over winter. New shoots grow from the roots in April, which are trained up supporting strings. The new bines will take only until mid-June to grow eighteen feet to the top of their support wires.

After being harvested, the cones are separated from the bine and leaves, and taken to the oasthouse for drying. The drying takes place in kilns at 60'C, where the moisture content of the hops is reduced from around 80% to 10-15%. A draught of air is maintained through the drying hops by means of an angled, rotating chimney which always faces away from the wind, so causing a downdraught. The hops are then packed into large sacks, called pockets, weighing in at around 85 kilos.

Lupulin glands develop on the inside of the hop petals. Lupulin is a sticky, resinous, oily substance which is only found in hops. It contains volatile oils, commonly referred to as as lupulins or beta-acids, which give beer flavour and aroma.

Also contained in the lupulin glans are resins, the most important of which are humulins, or alpha-acids. Alpha-acids impart beer with bitterness, and also preservative properties.

English hops are still acknowledged as the finest in the world, but hop farming has dramatically decreased in this country - in 1870, hops were grown on 72,000 acres spanning 53 counties in the United Kingdom; in 1995, there were just 200 farmers growing on 7,630 acres of land in Hereford, Worcestershire, Oxfordshire, Hampshire and the South-East of England. Today, there are fewer still.

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Categories
Hops are grouped in two main categories: bittering (or copper) hops, which are high in alpha-acids derived from the hop resins, and aroma hops.

There is a third category, known as dual (or general) -purpose hops, which are usually hybrid to combine reasonable bittering capability with good aroma.

Bittering Hops
Bittering (copper) hops are used for the main part of the 11/2 - 2 hour boil, to provide the beer its bitterness. However, it is during this period that much of the hops' aroma and flavour are driven off.

Aroma Hops
In order to compensate for the loss of aroma, an amount of hops are added for the last 10 to 15 minutes of the boil. This period is not long enough for the aromatic volatile oils to be driven off, nor for their bitterness to be extracted. This practice is known as late hopping, and it is usual to use a good quality aroma hop.

Dry Hopping
This is where a few hop cones are added directly to the cask when filling. This adds aroma to the finished beer, and is a practice often used by British brewers as it fully 'shows off' the fine flavours of English hops, contributing to the unique character of British cask ale.

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