As most people will know, aluminium cooking foil has a shiny side and a dull one. This is not deliberate, and is simply a result of the shiny side being in contact with smooth rollers when it is manufactured.
Personally, I prefer the shiny (smooth) side to be in direct contact with food because it seems logical that the smooth side is likely to stick to food less than the dull (and rougher) side. I have no evidence for this, and I am not claiming it is true – because it quite possibly isn’t. It just makes sense to me as a Chemist.
Another thing that makes sense is that if the dull side is rougher, then it has a greater surface area, so contact with anything acidic might result in more aluminium getting into the food.
About a month ago there was a story in the media where the chef Tom Kerridge claimed the shiny side should always face towards the food ‘because it radiates more heat back’.
I immediately thought that this was nonsense. If you are placing something in a metal tray, and lidding it with more metal, radiant heat is not really in the equation while cooking it. Yes, the shiny side will reflect more radiant heat than the dull one, but you are only using radiant heat to a significant degree in the oven if the food is uncovered and directly facing the flame or heating element. The rest of the time you are using conduction and convection heating – mainly the latter. There is certainly no radiant heat (as infra-red waves) trapped inside your foil parcel.
Incidentally, you can purchase non-stick foil. This has a coating on it which reduces sticking to food. Interestingly, they put the coating on the dull side – presumably because it sticks better to the rough side during manufacture of it. The packaging for this product specifically tells you to use the dull side against the food solely because that’s the side with the coating on it.
The funny thing was, I was listening to Planet Rock this afternoon and I heard Darren Redick ask Wyatt about this and they didn’t know. They asked people to email in with the answer, but I was just about to start a lesson so didn’t get to find out what had been said. Though I can guess.
The answer is that it doesn’t matter what side you have facing the food as far as cooking and heating is concerned. However, the shiny side might be less sticky and react slightly less with acid foods. And with non-stick coated foil, the side with the coating should be in contact with the food.