How do tamales cook?

Question

We just steamed a couple dozen tamales and I'm entirely baffled by the idea that they cook over hours. How? Why? What's happening?

I initially figured I could check for doneness with a temperature probe. After less than 30 minutes, the probe read 212 degrees throughout -- and obviously the tamal cannot heat beyond this point as we're steaming.

It was doughy and undercooked.

We left the tamales for another couple hours, as instructed, and voilà, the husk fell off neatly and the tamal was solid.

I don't understand.

212 degrees is well below the point where the Maillard reaction takes place. Is something else chemical going on? Is it purely physical -- maybe as simple as water boiling off?

I'm at a total loss as to the science behind cooking tamales, and it's driving me crazy.

Answer 1

To be specifically clear, what takes an hour (or more) is the starch gelatinization of the masa:

During heating and in the presence of excess water, starch granules initially imbibe (bind) water causing them to gradually swell and form a viscous slurry. As heating continues and temperature increases, the granules start losing their crystallinity becoming amorphous ...

Subsequent heating causes the granules size to increase until they can no longer absorb more water and burst. Rheologically, this is accompanied by maximum viscosity build up followed by a drop to a plateau. As molecules making up the granule start to leach out from the swollen granules and disperse/solubilize in the aqueous medium, yield a gel or paste whose properties depend on the concentration and type of starch in the slurry.

Just as the case for baking bread, it takes a considerable amount of time for the starches to go through these chemical and physical changes, and convert from a paste of cornmeal and water to a firm medium. The time required is further extended by the addition of ample fat (lard or butter) to the masa dough, which slows down the gelatinization.

Don't do the tamales with no fat, though, they really aren't good. Trust me on this one.

Answer 2

Cooking isn’t instant. You don’t just bring food to a particular temperature and then the physical reactions have happened and the food is done. Many of the processes happen slowly at the target temperatures. In fact, many of them also happen at room temperature - just way too slowly.

In the case of tamales going from squishy to not-squishy, that’s the starch granules hydrating, absorbing some of the water from the dough and cohering. This isn’t instant because it takes a while for the water to diffuse into the granules.

Answer 3

There are dozens, if not hundreds, of things going on, physically and thermodynamically, during cooking. The Maillard reaction is not especially important. It is just one of several types of browning, and it only serves to improve the taste somewhat, not to cook your food through.

The most important types of chemical and physical processes during cooking (and by "cooking", I mean applying heat to food, not other modes of preparation) are the denaturing of proteins, the breaking down of cellulose and hemicellulose in plant cell walls, the hydration and gelatinatization of starch, the dissolving of different molecules (e.g. sugars) in your cooking liquid or in the "own juice" exiting the cells, and the changes in aggregate state of lipids (which are much more complicated than the three phase transitions you learned in high school, with their amorphous solid state and tendency to emulsify). This is a rough list of what makes noticeable changes to texture and digestibility; there are also tons of reactions which influence flavor, or are unnoticeable by the eater.

Also, you seem to think that chemical and physical reactions are quick. Maybe high school chemistry is also to blame for this; the teachers tend to demonstrate quick-and-spectacular ones; sitting around watching iron rust does not make for good teaching. In fact, many chemical reactions are slow, and some of those in cooking are also slow.

In many cases in the kitchen, slow cooking is even preferred. It creates a much nicer, rounder taste, and sometimes a more pleasant texture. Tamales are intentionally designed for slow-cooking; both the steaming (which is slower than boiling) and the wrapping in leaves slows down the heat transfer, and ensures that they can sit around for a long time at heat without overcooking. So yes, it is perfectly normal for them to need a few hours even for the reactions which would be quicker in other dishes, such as the starch gelatinization, which is responsible for the sensory transition from "doughy dough" to "cooked-through-dough".