Why Not Just Use a Blender? Because It Leaves the Skins Behind

A blender reduces everything put into it, so skins become flecks, seeds become grit and fibre becomes a gritty suspension, all of which remain in the finished product. This device works by pressure and separation instead, with a curved blade sweeping food against a perforated disc so that the soft material is forced through the holes while anything that will not pass is left above. Tomato skins, apple peel, raspberry seeds and the fibrous parts of cooked vegetables are removed rather than incorporated. The output is smooth without being homogenised, since the material is pushed through rather than beaten, which is a different texture that cooks distinguish immediately.

The distinction is decisive in a small number of preparations:

• •Tomato sauce, where skins and seeds make a blended sauce bitter and gritty
• •Apple sauce, made from unpeeled fruit with the peel removed afterwards
• •Mashed potato, which a blender turns into glue and this device does not
• •Fruit purees for jelly and coulis, where seeds must be excluded
• •Soups thickened by their vegetables rather than by cream
• •Baby food, where fibre and skin are unwanted

Potatoes are the clearest illustration of why the mechanism matters, and the chemistry is specific. Potato cells are packed with starch granules, and the cells hold together in a cooked potato until they are ruptured. Beating with a blade ruptures them wholesale and releases free starch into the mixture, which then absorbs water and forms an elastic glue, and no amount of further work recovers it. Pushing cooked potato gently through holes separates the cells from each other while leaving most of them intact, so the starch stays where it belongs and the result is light rather than sticky. A ricer does the same job by the same principle, which is why both appear in recipes that forbid a blender.

Several kitchen implements separate or reduce food and confusing them leads to poor results. A ricer forces cooked food through small holes with a lever, producing the same cell-preserving effect for potatoes and doing nothing about skins, since anything entering must fit. A tamis is a drum-shaped fine sieve through which food is pushed with a scraper, giving the finest texture of all and requiring considerable effort. A chinois is a conical fine strainer used with a pestle for sauces and stocks. A colander drains rather than purees. A potato masher ruptures cells enthusiastically and is exactly what recipes warn against for a light result. Each suits a different combination of texture required and effort available.

These devices were standard domestic equipment across Europe and North America until the electric blender and food processor became affordable in the 1960s and 1970s, after which they were largely abandoned as slow and manual. That was a reasonable judgement for most tasks and a poor one for the specific tasks described above, and the tool has returned steadily since the 1990s, promoted by cookery writers pointing out that a machine which chops cannot also separate. Modern versions differ little from old ones, typically supplying three interchangeable discs with different hole sizes. Second-hand examples from the middle of the twentieth century work indefinitely, which is why they turn up constantly in charity shops and markets.

A blade chops everything and leaves skins, seeds and fibre in the mixture, while this device pushes soft material through a perforated disc and holds back whatever will not pass. That matters most for tomato sauce, fruit purees and mashed potato, where free starch released by a blade forms an elastic glue that cannot be undone. The tool was abandoned for electric machines and has returned because those machines cannot separate.