Sloe gin is a British red liqueur made with gin and sloes. Sloes are the fruit of Prunus spinosa, the blackthorn plant, a relative of the plum.
Sloe gin has an alcohol content between 15 and 30 percent by volume. However, the European Union has established a minimum of 25% ABV for sloe gin to be named as such. Sloe gin is technically a gin-based liqueur, but due to historical prevalence at the time of writing the EU spirit drink regulations, the colloquial name 'sloe gin' was included in the legal definitions and as such is the only gin-based liqueur that can legally be called gin without the liqueur suffix.
The traditional way of making sloe gin is to soak the sloes in gin. Most recipes call for the addition of sugar, but this is not required. The drink develops sweetness when the fruit is left in the alcohol and is allowed to mature. The addition of sugar is actually likely to inhibit the passage of flavor compounds from the fruit into the spirit, due to a reduction in osmotic pressure; a common criticism of sloe gin is that it is much too sweet.
Many commercial sloe gins today are made by flavouring less expensive neutral grain spirits, although some manufacturers still use the traditional method. US distilleries often use close relatives of the sloe, such as the beach plum, or more distant ones, such as the aronia berry, to produce a domestic version of sloe gin.