The microwave is a common household appliance, widely used for reheating food. It allows for very rapid heating without the need for preheating. For this reason, many food manufacturers try to design products that can be consumed after a brief stint in the microwave. However, when it comes to flour-based products like bread, cakes, or pizzas, this is not straightforward.

Why can’t we bake in the microwave?

Before explaining how the microwave works, let’s recall what happens during the baking process in products like bread or cakes. Conventional ovens typically operate at temperatures around 200°C. As soon as the dough enters the oven, the temperature of the outer part quickly rises to 100°C, at which point the energy is directed towards evaporating water. Heat progressively penetrates towards the interior, and some of the evaporating water is replaced by moisture from the inside of the dough. Since the evaporation of external water is faster than its replenishment, the crust forms. This dry layer continues to increase the temperature progressively, facilitating Maillard reactions and caramelization of sugars, which create the typical toasted colours of bread and cakes. Meanwhile, the interior of the dough gradually increases in temperature but never exceeds 100°C, as the water does not completely evaporate. This, combined with the formation of the crust, keeps the dough somewhat moist. We will delve deeper into the reactions occurring during baking later.

In the case of microwave ovens, they rapidly change the polarity, causing dipolar substances to rotate. Most dipolar substances are water molecules present in food. This rotational movement causes molecular friction and subsequent heating. Unlike conventional ovens, this heating occurs uniformly throughout the dough. Since water molecules are responsible for the heating, the temperature never exceeds 100°C, or at least not significantly. Consequently, the interior of the dough reaches this temperature much earlier than in conventional baking, promoting the dehydration of the dough, resulting in microwaved products being drier and harder. Moreover, the exterior of the dough does not surpass 100°C, preventing the Maillard reactions and caramelization of sugars, leaving the outer part whitish. Additionally, the characteristic crust in bread does not form.

Possible solutions

For bread, no suitable solution has been found. Therefore, when you need to heat a baguette, it is preferable to use a conventional oven (also for finishing par-baked bread) or a toaster or griddle. These appliances allow reaching high temperatures in contact areas, creating a crispy texture, brown colours, and toasty flavours. However, some flour-based products can be “cooked” or finished in the microwave. The most common ones are certain types of cakes and pizzas. Let’s break it down:

Cakes

For cakes, there are ready-made mixes designed for microwaving or powders that, when hydrated, can be finished in the microwave. It is essential to note that these products, unlike bread, do not have a pronounced crust (dry outer part). They also incorporate fats and oils in their composition, contributing to juiciness in the final product. If you know of such products, you will notice they are typically chocolate-flavoured. In these cases, cocoa fat enhances the final juiciness, and the colour of the outer part, similar to the interior, depends more on the chocolate than on Maillard or caramelization reactions. Microwave-ready mixes may also include a substance to provide a toasted colour, often using ground cookies or another brown-coloured product. To minimize water loss during baking, hydrocolloids, substances with high water retention capacity, can also be incorporated. With these conditions, a cake can be made in the microwave, which may taste good, although it will never be quite the same as one baked in a conventional oven. If you have a cold cake and want to warm it up a bit, you can also microwave it for a few seconds.

Pizzas

The case of pizzas is different. These products, usually marketed as par-baked, have a lower dough portion that should be toasted and crispy after baking, requiring temperatures above 150°C in this process. On the other hand, the upper area, where the toppings are located, is typically desired to remain juicy, so excessive heating can be counterproductive. If you have seen pizzas designed to be finished in a microwave, you will notice they often come with a metallic cardboard advised to be placed underneath when “baking.” This cardboard is made with materials called “susceptors”. These materials reach very high temperatures when exposed to microwave action, mimicking the effect of the oven floor. Therefore, the combination of a good susceptor material, a juicy topping that will not suffer from possible dehydration during baking, and a thin crust allows achieving pizzas that can be finished in a microwave.

Susceptor materials have also been used to make other products that need to be finished in the microwave, but with much less success. For example, there was once a puff pastry similar to “pain au chocolat” that had to be placed in a susceptor “pouch” for heating. To obtain a quality product, it was necessary to modify the fats used to make the puff pastry, and as the contact between the pouch and the product was uneven, the results were not as good as with pizza. It was eventually withdrawn from the market.

Other considerations

It is also essential to consider that microwave ovens have advanced significantly, and there are now some that can combine different types of heating. In these cases, the possibilities are much greater and require careful study. However, when manufacturers develop a product, they usually focus on appliances found in most homes. In the case of microwaves, they are not usually very complex and, at most, have a resistance in the upper part for toasting a bit, something that is not usually sufficient for obtaining quality bread.

Finally, it should be noted that, no matter how much we regulate it, it is challenging to find two microwaves that work the same way. This makes the time recommendations given by manufacturers, which must be uniform for all consumers regardless of the microwave they have, often unreliable, and we must adapt them based on the equipment we have. This made many manufacturers reluctant to develop microwave products at the time. However, the success of the products launched, thanks to the convenience of this equipment compared to conventional ovens, has encouraged many manufacturers to try to develop products suitable for this type of heating.