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why does aluminum foil have dull and shiny sides

ItБs a well-established question, and one that weБve been too afraid to ask our mothers: Should we use the shiny or the dull side of aluminum foil when we cook? And have we been doing it wrong this entire time?! Concerned cooks, you can breathe a sigh of relief: As it turns out, thereБs no БcorrectБ side of aluminum foil to use when cooking. According to the, theyБre both equally effective at heatingбyour foodБso just choose whatever side you prefer. (Not a cook? You can also. )
If there s no trick to it, then why, exactly, does aluminum foil have a shiny and a dull side in the first place? Experts at say that the difference between the two sides is due to aб manufacturing process called milling, duringб which heat and tension is applied to stretch and shape the foil.

Two layers of foil are pressed together andб milledб at the same time, because otherwise, it would break. БWhere the foil is in contact with another layer, thatБs the БdullБ side,Б ReynoldБs explains. БThe БshinyБ side is the side milled without being in contact with another sheet of metal. The performance of the foil is the same, whichever side you use. Б But pay attention if you are using non-stick foil; in that case, there is a difference between the two sides. Since the non-stick coating is only applied to one side, youБll want to use the dull side.

Side note: There will be a label thatб designates theб Бnon-stick sideБ in case you forget. However, Бso maybe you should stop cooking with it altogether. [Source: ] More:, Why does household aluminium foil have one dull side and one shiny side? SO THAT the shiny side can reflect the heat on to the item to be cooked, using a long-established scientific principle that shiny surfaces reflect heat and light. What has completely mystified me for years, though, is the fact that 99. 9 per cent of people I have come across use aluminium foil the wrong way round - with the shiny side outside - thereby reflecting heat away from what they are trying to cook.

A SIMPLE experiment will show that - contrary to Joyce Masse's suggestion - the dull side of aluminium foil reflects as much heat as the shiny side. Turn your kitchen grill fully on and place your hand by the side of the grill out of direct line of sight of the element. A piece of aluminium foil held in front of the grill may now be used to reflect the heat from the element on to your hand where the warming effect may be easily detected. I have tried this but have been unable to find any difference between the heat reflected by the dull and shiny sides. A surface only appears shiny if its roughness is less than the wavelength of light. Since heat is transmitted by infra-red rays which have a longer wavelength than light rays, it is perfectly possible for a dull-looking surface to be 'shiny' as far as heat is concerned.

IN ORDER to roll aluminium down to the thickness (or thinness) required for cooking foil (approximately 0. 01mm), two coils of aluminium strip have to be passed through the rolling mill at the same time - a process called 'doubling'. The result is that the external side then has a shiny finish and the internal side is matt. The idea that the difference in finish enhances cooking is simply a marketing ploy by the foil producers, who could not make it shiny (or dull) on both sides even if they wanted to.

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