heat transfer?

[Donna Manion]

I have a CI skillet that is not a spinner. As a matter of fact, it bows up in the middle about 1/32 of an inch. It has a 9 inch bottom and the burner on my glass top stove is 9 inches--seems like a perfect fit. However, when I cook grilled cheese sandwiches in it, they get done faster in the middle of the pan than toward the edges. I have to flip and move a sandwich around to get it done evenly. That is not a problem with my SS pan.

What causes this?  Thanks!

[Adam Hoagland]

[size=12]I'm guessing it's due to the upwarp.  A downwarp will make a pan spin, since the center contacts the flat stovetop and the edges don't, but if you've got an upwarp, even though the pan doesn't rock around or spin, the (flat) food is pressed against the hot iron in the center of the pan, but is slightly raised (or just not as closely pressed against) the hot iron all the way around the edges.  If there's a miniscule airspace, the edges won't cook as fast while the center burns.  Also, if you're using liquid cooking oil, it may be flowing away from the upwarp to the edges, and that may be contributing the same way an airspace would.

I'm not speaking from experience -- I have a cracked user Wal-Mart Lodge skillet, but I don't think I'm using anything with an upwarp.  It just makes sense to me that this may be what's happening to you.  Is the Stainless Steel skillet also warped, or is it still perfectly flat?[/size]

[Russell Ware]

Stainless steel is much thinner than cast iron; so that can account for the difference in pan performance. The steel pan will preheat more quickly. To try to diagnose cast iron heating issues, I use an infrared laser thermometer. Your burner setting may be too high, and that’s why the center is cooking faster. Cast iron takes a while to heat uniformly, but once heated, it holds that heat very well. Even though you are using a glass top stove, it doesn’t mean that the burners heat evenly. They can have hot spots.

[Donna Manion]

Thanks, both of you, for your responses.  I'll add a few more comments and questions--

1--My SS pan actually has a 1/4-inch bottom; it's pretty heavy for a SS pan.
2--I didn't know the burners could have hot spots; I'll try it on the other 9-inch burner next time.  And of course I guess it's possible that all these burners are just hotter in the center than they are on the outer edges....
3--Is it possible that the small 1/32 inch of upwarp (new word for me--my computer doesn't like it!) would trap heat and make the center of the pan hotter than the edges? 
4--If yes, would the heat level out as the pan warmed up, or would it stay hotter in the center for the duration of the cooking?
5--I buttered the bread for the grilled cheese sandwiches, so there's no oil/butter to run to the sides of the pan.
6--Do upwarped pans work better on gas stoves than they do on electric?  (I have always watched out for wobbly pans but thought I was safe if they "sat flat.") 
7--Is it possible for one person to have more questions??   :D

[Tom Neitzel]

Donna, I've found that for every question you find an answer, there are five more that come with the answer.  You've clearly found the right hobby.

Now to add a little more to the discussion.  I've attached a picture of some current advertising from a major Swedish foundry.  They say a pan like yours is best for the glass top stove.  I believe they are stating that as the pan heats it will bow down and make flat contact with the heat.

I tend to agree with Russell's comment, it may be the uneven heat from the element.  Harbor Freight has thermometers that will measure up to nearly 1,000F at a pretty reasonable price.  They have 20-25% off coupons all the time in magazines and newspapers.

http://www.harborfreight.com/non-contact-infrared-thermometer-with-laser-targeting-60725.html

Tom

[Valerie Johnson]

1--My SS pan actually has a 1/4-inch bottom; it's pretty heavy for a SS pan.

Many newer pans have these thick bottoms which is used to distribute the heat evenly.

The 6mm stated in Skeppshult ad translates to apx 1/4" thick.

[Donna Manion]

Tom and Valerie, thanks for the information. 

Tom, there's a Harbor Freight not far from me, so I'll look for a coupon, then go over there and see what they have in the way of thermometers.  I guess I can shine it on different places on my burners to see what's up with the heat.

It would be interesting to see one of those Skeppshult skillets, wouldn't it!

[Jim Glatthaar]

Donna, for a while I used an infrared thermometer to make sure my vintage cast iron pans were properly preheated.  But now I know that 10 minutes over low or medium low heat will suffice.  But the infrared thermometer is a great tool to learn with.

[Ken Davis]

Is it possible for the upwarp to cause the heat to concentrate toward the center?

[Russell Ware]

Is it possible for the upwarp to cause the heat to concentrate toward the center?

An upward warp means the center of the pan is farther from the heat source. Therefore it would be cooler than the rest of the bottom. A spinner has a downward warp, so the center on that pan should be the hot spot.

[Keith Rumgay]

Lots of information for a toasted  cheese  sandwich  ;D ;D