used to crush the tissue Mashing by hand leaves large cell aggregates intact; the screens in food mills and strainers produce smaller pieces; machine-powered food processor blades chop very finely, and blender blades, working in a more confined space, chop and shear more finely still Persistent celluloserich fibers can be removed only by passing the puree through a strainer 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 oxygensensitive 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 (p 269) 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 Foams and Emulsions The cell-wall carbohydrates in purees and juices can be used to stabilize two otherwise fleeting physical structures, a foam of air bubbles and an emulsion of oil droplets (pp 638, 625), which are especially easy to prepare with modern electrical blenders and mixers If a puree or juice is whipped to fill it with air bubbles, the cell-wall carbohydrates slow the flow of water out of the bubble walls, so the bubbles take longer to collapse This allows the cook to ... just the traditional ones Foams and Emulsions The cell-wall carbohydrates in purees and juices can be used to stabilize two otherwise fleeting physical structures, a foam of air bubbles and an emulsion of oil droplets (pp.. .and change rapidly Apple and pear juices turn brown, for example, thanks to the action of browning enzymes and oxygen (p 269) If not used immediately, they’re best kept chilled or... 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