The common juniper tree (Juniperus communis) is a coniferous plant and a member of the Cupressaceae (cypress) family. It has the widest geographical range of any tree in the world, taking up residence in western Alaska, throughout Canada and northern parts of the USA, in coastal areas of Greenland, in Iceland, throughout Europe, north Africa, and in northern Asia and Japan. Juniper is quite content in either acid or alkaline soils and examples can be found across a variety of landscapes. At its southernmost extent it has been recorded at elevations of up to 3,500m. Suffice to say that if you live in the northern hemisphere, you probably live close to some juniper.
Common juniper can grow up to 10 meters in height and live for over 100 years, but those cultivated for gin production are engineered to be much shorter and bushy.
Juniper is a slow-grower, it takes a leisurely ten years before the plant produces flowers and fruit. Juniper is dioecious (as well as being delicious) which means that individual plants are either male or female, unlike most tree species, where both male and female flowers occur on the same tree. Male flowers present themselves as yellow blossoms near the ends of the twigs in spring and disperse pollen in to the wind. Female flowers are in the form of very small clusters of scales, and after pollination by the wind, these grow on to become tiny cones. It’s these cones that soften and develop in to the juniper berry that we know and love.
Shaped like irregularly-sided spheres, juniper berries are green at first, but ripen only after 12 - 18 months to a dark, blue-purple colour. They’re about 0.5 - 1cm in diameter when fresh. Each berry contains 3 - 6 triangular seeds, which are dispersed by birds which eat the berries. Given that it takes so long for the berries to ripen it’s normal to see both ripe and unripe fruit on the plant at any one time. This means the same tree may be harvested three times over a two year period.
Most of the juniper used to make gin is sourced from Italy or Macedonia, although there are examples of juniper sourced from Netherlands, Bulgaria and Albania. Juniper can still be found in the UK, especially Scotland, but the fungus Phytophthora austrocedrae has decimated up to 70% of Britain’s juniper in recent years and in general the tree is at risk of extinction throughout the British Isles.
It’s surprising to find that most juniper trees are not farmed or cultivated and picking is more akin to foraging than harvesting. In the traditional manner, pickers will circulate around a tree, beating the branches and catching the falling berries in a round flat basket. On a good day, an experienced beater might be able collect their own bodyweight in berries.
The earliest recorded use of juniper medicinally dates back to ancient Egypt and around 1500 BC when the brown coloured fruit of Juniperus phoenicea was used as a poultice to treat musculoskeletal disorders (joint and muscle pain), consumed orally as a cure for tapeworms, and used to induce child birth — the effectiveness of which has been validated by modern pharmacological studies. Athletes in Greece’s ancient Olympic games gobbled up juniper berries, believing they would improve performance. The Roman’s used juniper for a range of digestive ailments, and famous mediaeval herbalist Culpepper used juniper infusions for the relief of trapped wind, for which juniper oil is still used today. During the 1918 Spanish flu epidemic, hospitals experimented with spraying vaporised oils into the atmosphere of flu wards in an attempt to prevent airborne infection spreading, and juniper was one of those found to be particularly effective. Extracts of juniper are still used today in alternative medicine for the treatment of skin problems like dermatitis, acne and athletes foot.
The highest concentration of juniper oil is actually found in the seeds of the fruit, rather than the flesh or skin.
The volumes of both juniper oil and its constituents can change quite dramatically according to the the berries ripeness, the age of the plant, period of harvesting, and terroir. In general, the essential oil content of juniper cones peaks at around 3% just before the fruit reaches full ripeness. Over 70 different components have been identified in the oil of juniperus communis, but it is largely made up of five flavourful terpenes:
Pinene is the predominant terpene in juniper, and there’s no prizes for guessing the aroma that it imparts. There are actually two types (isomers) of pinene in juniper: α-pinene, the principal of the two, is one of the most widely encountered aromas in nature, and used by coniferous trees as an insect repellant. It has a woodsy cedar-like aroma. β-pinene is found in much smaller quantities in juniper, generally one-tenth than of α-pinene, and it can be distinguished by a green, Christmas tree type aroma.
Mycrene is perhaps the second most important terpene in juniper after pinene. It’s also found in thyme, bay and hops, and gives us a lingering herbal, mossy, aroma. Sabinene gives juniper a warm, slightly nutty aroma. Limonene provides freshness and citrus notes.
One 2011 study conducted jointly by the University of Vienna and University of Food Technoligies in Bulgaria found that levels of α-pinene across 13 samples of Macedonian juniperus communis ranged from 16-43% (the modal average being about 22%) of the oils total composition. Pinene content has arguably the biggest impact on gin flavour intensity, so where infrastructure permits producers will carefully assess samples before committing to buy.