Aluminium foil is produced by repeated thinning of a large block of aluminium.
To begin with, big blocks are melted at 750 oC for hours, impurities are removed and small amounts of other elements are added.
Then this pure aluminium mixed with other elements is solidified and converted into long, thick slabs called ingots (weighing thousands of kilos).
The ingot, which is about 45 cm in thickness, is passed 12-16 times through heated rollers (over 450 oC) to achieve the thickness of 5mm.
When 5 mm thick, the aluminium sheet is rolled on a cylinder-shaped machine and transferred to a set of cold rollers (they roll the sheet from top and bottom).
The foil is then pressed on the cold rollers multiple times to reduce the thickness further (a typical household aluminium foil is 0.016 to 0.024 mm).
By the time the foil gets to the final press, it is so thin that it could break.
So, the manufacturers push through two sheets together at the same time for the final press.
The sides of the sheets that come in contact with each other end up with a matte (dull) finish.
And the sides that come in contact with the highly polished steel rollers become shiny.
So, for wrapping food, we can use either side.
However, there are certain foils which claim to have a non-stick side, i.e. one side of that foil is coated with a substance that will keep the food from sticking to it.
For these foils, we should place our food on the non-stick side.
