Why do you cook with the shiny side of the tinfoil in?

June 17, 2006 4:28 PM

When cooking with tinfoil, why do you put it with the shiny side towards the food?

If we cooked food by shining bright lights on it, it would make sense to put the light-absorbent side out — but we don't (usually) cook food that way. If we cooked food until it became glowing hot, it would make sense to put the reflective side in — but we don't do that either.

In fact, I was under the impression that most cooking techniques worked by conduction or convection, not radiation. So why do the reflective properties of the foil matter at all?

posted by nebulawindphone to science & nature (17 comments total)

I never pay any attention to it, but I'm not much of a cook. I suspect the idea is to maximize reflection of IR from the food. But it also might be to decrease the amount of aluminum that gets dissolved by acid from the food. (Not that aluminum is poisonous in small quantities, but just to try to avoid it changing the flavor of the food.)
posted by Steven C. Den Beste at 4:35 PM on June 17, 2006

It just doesn't matter. The difference in the shiny/dull side is simply a result of the manufacturing process.
posted by walleeguy at 4:41 PM on June 17, 2006

As said earlier, it doesn't matter at all. When aluminum foil is manufactured, it's so delicate that the presses that flatten it will tear it unless two sheets are pressed together. Thus, the shiny side is the side that presses against another sheet. Neither side conducts heat any better or worse than the other.
posted by trey at 4:42 PM on June 17, 2006

I had always understood this to be about reflecting whatever heat is radiated from the food. I had also always understood that the effect, if any, was so miniscule as to make no detectable difference whatsoever.

You can confirm this by wrapping two similar potatoes, one shiny-side in, one shiny-side out, and baking them side by side in an oven. They both bake fine. They also bake fine if they are double-wrapped or not wrapped at all.
posted by ikkyu2 at 5:06 PM on June 17, 2006

When I bake and line a pan with foil, I do it shiny-side to the food because I assume that its smoother and therefore less likely to stick to the food. I doubt it really makes much difference though, especially since I grease the foil anyway.
posted by Good Brain at 5:15 PM on June 17, 2006

Because we are trained to do so. We know sheets have 2 sides and the better side needs to be up, blankets, etc... A infoil has 2 sides too, the better looking side might as well be up or touching the food. Even if it does not make any difference.
However, Good Brain is correct, I also believe that the shiny side will be less likely to stick to food, even on a micro level with heat and leave residents stuck to the food that I don't want to consume. The latter might as well be not true, but it is a reason nonetheless.
posted by convex at 5:27 PM on June 17, 2006

We are trained from birth to believe that Shiny == Good. You don't want The Bad Side touching your food, do you?
posted by SPrintF at 5:46 PM on June 17, 2006

I put the dull side towards the food.
posted by thirteenkiller at 7:35 PM on June 17, 2006

shiny-side in helps keep the secret mind control transmissions IN the food.
posted by ab3 at 7:55 PM on June 17, 2006

It matters not.
posted by caddis at 8:06 PM on June 17, 2006

I put the shiny side on the outside too. It looks better.
posted by Who_Am_I at 8:44 PM on June 17, 2006

I have never heard any of my chefs at school or work ever comment on this, so I hardly think it matters, as far as the actually cooking goes. Sticking to the foil might be the only consideration...and even then you can spray or oil the foil.

ab3 might be closest to the real answer.
posted by BradNelson at 10:09 PM on June 17, 2006

The Straight Dope says it doesn't matter. From the article:

The truth is that the shiny side is not treated with a dangerous chemical. Mineral oil is used as a lubricant during the rolling process, some trace of which may remain on the finished foil--but it's not dangerous. The shiny side is shiny because of the way foil is made. During the last pass through the rolling mill, a double thickness of foil is run between the rollers. The side of each sheet that comes in contact with the polished steel rollers comes out shiny. The other side has a matte finish.

Having dispensed with the paranoid rumors, let's get down to heart of the matter. Are you supposed to wrap stuff shiny side in or shiny side out? (We'll pass over the issue of whether you ought to be wrapping spuds with foil in the first place, a practice that many regard as folly.) The official word from the Reynolds aluminum people is as follows: "It makes little difference which side of the Reynolds Wrap aluminum foil you use--both sides do the same fine job of cooking, freezing, and storing food. There is a slight difference in the reflectivity of the two sides, but it is so slight that laboratory instruments are required to measure it."
posted by lekvar at 10:53 PM on June 17, 2006

We wrap with shiny side in because those are the rules of this household, young man!

Actually, I was never taught that either side was better, and I've never paid any attention. I suppose I have a mild preference for shiny side out because it looks cooler that way.

Being only moderately knowledgeable about how heat transfers through foil, if I'd ever bothered to think about it, I'd probably have put the matte on the outside, assuming that it would absorb heat a little better. Wouldn't surprise me if other people thought the same way.
posted by Malor at 11:24 PM on June 17, 2006

Walleeguy got it. I just saw the Reynolds Ladies on tv and they said this exact thing.
posted by Terminal Verbosity at 6:37 AM on June 18, 2006

Wow. I've never heard of anyone putting the shiny side in, and I've worked in plenty of kitchens.
posted by Mr. Gunn at 7:47 PM on June 18, 2006

Cooking, it matters not. All in the creation process.

But it does matter when making protective hats and garments, as ab3 alluded to.....shiny side out!
posted by mattfn at 1:24 PM on June 20, 2006