On Taking a Temperature

Reader Annemarie writes:

So Joe, can you enlighten me where in a pan are you supposed to take a thermometer reading? I was making a lemon tart (Heston Blumenthal’s recipe sorry) at the weekend and it says to take the custard to 62C, I was using my thermometer but depending on where I put it I got different (like much different) readings. I was bringing this custard up over a pan, and I must have stood there for an hour stirring stirring stirring until I finally thought “oh blow it” and bunged it all in the tart case and put it into the oven…it came out perfect by the way, but what a faff!

I think pretty much everyone has had a similar experience, Annemarie. Glad it worked out in the end. Temperature variations like that occur in all pans, especially if they’re broad and shallow. So to begin with you want to select a saucepan that’s thick, deep and with high sides, hopefully one that fits squarely over the heat source. The idea here is that a thick-sided pan will distribute the heat more evenly, and keeping the custard (or whatever it is) compact will not only help with heat distribution, but will cut down on evaporation which cools the mixture (my feeling is that evaporation is what was causing the extended cooking in your case).

Next, even with the thickest, tallest pan you’re going to get temperature variations to some extent. Personally I try to combat that by gently whisking the liquid I’m measuring to try to compensate for any hot spots. Tipping and swirling the pan also helps in this regard, especially if the liquid is only a couple of inches deep. I then insert the thermometer smack in the middle of the liquid, about two inches down at the deepest point. That to me is the most reliable place to take the temperature.

Of course being uptight I’ll usually swizzle the mixture a little more with the thermometer and wait another couple of seconds to see if there’s much variation. That’s pretty much how I do it, but I’ll welcome any other insights from readers. Thanks for the question, Annemarie!