What happens if you cook chocolate pudding too long on a double boiler?

Question

I am having some troubles getting my pudding consistency right.

The kind of pudding I am trying to make is of just milk, cream, sugar, cocoa and cornstarch. The double boiler I use is a small pot in a slightly bigger pot, filled with water.

Until now my pudding almost always turned out runny, like a thick sauce. Then I had the revelation that this happens when the water level in my big pot drops below the smaller pot, so that only the vapours are transferring heat to it (I am guessing in my case it doesn't work, since there is a gap between the pots and thus the temperature can't escalate much in this way). So I sort of solved this problem by adding more water. This allowed me to get one pudding right (or so I think) but then the next one was runny again. I got pissed and thought I simply hadn't cooked it enough (I usually take it off the stove when I think it is the right thickness, wait for it to cool down and refrigerate overnight). So I put it on the stove again and left it there for a whole lot of time ~50 minutes or more (I have an automatic stirrer to stir it, first fast, then slowly to let the starch coagulate). And THIS time it became so thick I think it can rightfully be classified in a solid body state. There is no hint of runny-ness, but now it is really hard and gooey, when pulled it stretches sort of like taffy or thick gum, it holds a solid shape and you can't "scoop" it with a spoon, instead you only pull it. It is also a darker color than usual, so I am wondering if I might have burned it or just added too much starch or sugar (this time I was experimenting with more sugar)?

All I knew, the double boiler prevents any burning (in my case there are no burn marks, but maybe the milk got burned/heated too much?) and cornstarch, once heated to the sufficient temperature, would just thicken and further heating it wouldn't change anything, unless it is TOO much heating.

My recipe is:

• cocoa 150ml
• sugar 500ml
• cream 50ml
• cornstarch 100ml
• milk 800ml

(I measure in ml, don't ask)

So, if nothing was burned or heated too much, it could be that roughly a third of the entire mixture is sugar, while only half is milk and maybe 1/16th of the entire mixture's volume in cornstarch is too much? I have never gotten a definite valid correct sample with this recipe to be able to compare to anything and it will be some time before I can experiment again.

Answer 1

Try using a heat diffuser for your hot plate/burner. You can get them quite inexpensively on Amazon and other places.

Answer 2

It is a bit difficult to address all the points in your question, as it mixes up observations, assumptions and a very strange recipe, but I'll try.

There are three types of sweet dessert relevant here. I'll call them custard, pudding and taffy, although the names are not used with perfect consistency everywhere.

Custard is dairy thickened by egg yolk. It requires very tight temperature control, as it starts forming at 60 Celsius (but that won't be sufficient for a standard custard) and overcooks somewhere around 85 Celsius, turning grainy and unpleasant. To prevent that, custard is cooked in a double boiler, which makes the mixture heat up slower and more evenly. So the answer to your title alone would be, "it curdles".

A pudding is dairy thickened by starch. It needs to arrive at close to 100 Celsius to thicken properly (there are a few degree Celsius difference for different types of starch, all work between 95 and 100 Celsius). Your yolkless pudding shouldn't be in a double boiler in the first place, as it normally keeps the temperature way too low. A starch pudding is prepared by mixing the starch into a small portion of the cold dairy, heating the main portion of the dairy and adding the starch mixture, then mixing constantly until it has boiled. At that point, it thickens and the boiling actually consists of a few blubbs. The thickness/runniness is controlled by the amount of starch you choose (10% of the dairy for standard pudding), not by reducing the temperature. It is a bit more difficult for chocolate pudding, as cocoa powder is partly made up of starch, you might need to experiment with ratios. Also note that ratios are measured in weight, not volume.

A taffy is caramel softened with some dairy. The more typical way to make it is to make the caramel first, then add the dairy. But there are also methods for heating everything together and waiting until a large proportion of the water in the dairy evaporates and the sugar manages to darken. It has the side effect of also caramelizing the milk sugars, giving it a more dulce de leche like effect. While I would have expected it to need a bit more temperature, this is the best explanation I see for your experience. "Stretches" and "can only pull it" are prime examples for describing taffy, and I cannot imagine any other reason for getting this effect with your ingredients. Starch certainly doesn't behave this way no matter how overheated (it simply chars).

The best advice I can give you: decide what you want to have (custard, pudding or taffy), find a recipe for it and follow it. It will have both the ratios and procedures. Then you won't end up doing counterproductive stuff like using a boiler on a starch pudding or oversugaring it.