September, 2011

The hardest part of cooking is knowing when to stop. Gummy pasta, rubbery squid and dull mushy vegetables are the sad victims of rampant intemperacy. Instead of receiving a clear signal announcing "done", we are expected to divine a food's intentions by thumping on a loaf of bread, pressing a steak for doneness, or discerning the subtle difference between soft and hard peak mereigne. Sometimes, only an extra minute of cooking divides success from failure.

But with a little science, and a hint from low and slow barbecuing, we can often stretch this window from minutes to hours. And even discover a new way to cook bread along the way.

Normally, time or temperature are the main signals to move from stove to table. A hamburger is rare at 125F, medium at 135F and well-done at 145F. Chilis or stews, are ready in "six or seven hours", shrug off hours of gentle bubbling on the stove.

But other foods resist simple metrics.

Most breads are baked in relatively hot ovens- typically around 350F, but sometimes more than 800F for pizza. A pizza may cook for only 90 seconds at these blistering temperatures- as you can imagine, it moves from soggy to burnt in the blink of an eye. Even a loaf of bread only offers a narrow window of success- out of a 35 minute baking period, perhaps a 5 minute window.

This graph follows the internal temperature of a roll and a loaf of bread during baking in a 350F oven. Note how the temperature rises quickly to nearly the boiling point of water (212F) around the time the bread is perfectly cooked. A hand-held instant read thermometer is nearly useless in this situation- you would have to constantly open the oven, stab the bread and repeat mulitiple times, around that 5 minute window. While letting humidity and temperature escape. Not a likely scenario.

You *could* bake bread by inserting a tethered digital thermometer into the raw dough (as I did to generate the above plots). I've found that most breads, depending on the recipe and taste preferences, are ready just as the temperature is reaches 205F to 210F. But you still have to watch the thermometer- because, as you can see from the above plot, once the bread reaches 210F or so, it "stalls" at this temperature, even while it moves from perfection to a floury brick.

This plateau is remeniscent of the stall meat experiences when cooked "low and slow" in barbecue. The physical origin of the stall is simple- moisture migrates from within the meat to the surface, where it evaporatively cools, supressing the meat's internal temperature below the oven's temperature.

Meat contains "free" water that is not chemically bound to proteins, so it can be released at low temperatures. But bread absorbs almost all the water into hydrating starches and glutens. Only near the boiling point of water is this gently bound water freed up to evaporatively cool the bread.

We can see this difference in the following plot- comparing the stall temperature for a tray of water to a lump of bread dough:

Pure starch follows the dotted lines- bread dough contains milk and fats which somewhat stretch the stall out in temperature.

Still, this curve does provide a bit of inspiration- if meat develops strong flavors and tenderness by low and slow cooking around 225F, why not bread?

--------------------------------------------------------------------------------------------------------

Additional articles on kitchen science can be found HERE.
  Or follow me on twitter for (very occasional) alerts of new food science postings at @KitSci
In the practice of all-things barbecue, we appreciate the support and conversations with Meathead at AmazingRibs.com, Sterling at BigPoppaSmokers, along with numerous competition pitmasters and backyard chefs.