Gin starts as a neutral spirit, much like vodka. Botanicals are added during the distillation process and left to steep. Some producers place the botanicals in a tray over the spirit as it distills. Pure water is then added to reach the required strength of about 45% ABV (Alcohol By Volume).
All gins include juniper as an ingredient. Some other botanicals used include coriander, angelica, orange peel, lemon peel, cardamom, cinnamon, grains of paradise, cubeb berries and nutmeg.
There are basically four types of gin. London Dry, Plymouth, Old Tom and Dutch gin, also known as Genever.
London Dry is far and away the most popular and is found in almost all mixed drinks and cocktails.
Plymouth gin is similar to London Dry but slightly sweeter and fruity.
Old Tom gin is also similar to London Dry in most ways, but is somewhat less versatile. Old Tom is bottled with the addition of simple syrup that gives it an added sweetness.
Dutch gin is smooth-bodied, sweet and flavorful. It lacks the sharpness of London Dry gins, but makes up for it with a nice rounded flavor. This type of gin can be aged up to three years.