Two kinds of juicers exist—a manual, or hand-operated, version and an electric version.
Juicing consists of placing fruit wedges or vegetable slices cut side-down in the center of the juicer and then pressing down to squeeze the food and moving it back and forth so the juice will run out of the rind and away from the pulp. The pulp and seeds are collected along the edges of the juicer, and the rind it then discarded.
Electric juicers mechanically extract juice from fruits, vegetables, herbs, etc. Proper operation consists of placing the article of food within and pressing the button. The juicer then automatically squeezes juice out of the food. Because of its mechanical nature, electrical juicers are far more dangerous than manual ones, and so it is important that users be taught how to properly use them.
Two kinds of electric juicers are on the market:
Centrifugal juicers—these consist of a blade and sieve to separate juice and pulp from rinds or outer shells or casings. Centrifugal juicers cannot break fibres in food, so their use is limited.
Masticating juicers—these ‘chew’ up the entire piece of food before, or in order to, squeeze juice from the inside. When the food becomes mangled, the juice naturally flows out. Masticating juicers can break fibres in food, so they have a much wider use than centrifugal juicers.
By the way, electric juicers and blender are different in function and purpose. Electric (masticating) juicers are able to separate juice from fibers, whereas blenders, like centrifugal and manual juicers, cannot.
The theory is that since fast-moving mechanical parts of an electric juicer blow air into the food, causing greater and quicker oxidation to important nutrients, electric juicers, especially those having variable speeds, are considered to be of higher quality than manual juicers. This has not been proven, although it is a common belief.