Juices

Juices are refined versions of the puree: they are mainly the fluid contents of fruit and vegetable cells, made by crushing the raw food and separating off most of the solid cell-wall materials. Some of these materials inevitably end up in the juice— for example, the pulp in orange juice—and can cause both desirable and undesirable haziness and body. Because juicing mixes together the contents of living cells, including active enzymes and various reactive and oxygen-sensitive substances, fresh juices are unstable and change rapidly. Apple and pear juices turn brown, for example, thanks to the action of browning enzymes and oxygen. If not used immediately, they’re best kept chilled or frozen, perhaps after a heat treatment just short of the boil to inactivate enzymes and kill microbes. Modern juicing machines can apply very strong forces, and make it possible to extract juice from any fruit or vegetable, not just the traditional ones.