The processes taking place in the furnace - Neumann 1929

[Dough changes during baking.]

"PROCESSES OCCURRING IN THE BREAD FURNACE". From the book of Prof. Neumann "Grain and Bread". 1929 g.

Dough changes during baking.
The changes that the dough undergoes during baking are naturally the same as in flour when heated. We know that starch grains in a wet state gelatinize at 65 ° Celsius, that protein substances coagulate at approximately the same temperature, passing from a viscous swelling state to a solid one. Since starch and protein are the main constituents of flour, we will consider these changes the most important. They proceed as follows.

The first effect of the furnace heat will be that the fermentation gases contained in the dough expand, which means they take up more space. Thus, the viscous, resisting mass of the dough rises even higher; thanks to the enlargement of the pores, the dough expands even more. Practitioners say: "bread rises in the oven."

At the same time, in those places where the dough is most exposed to heat, therefore on the underside of the bread, which is in contact with the hearth, and on the surface on which the top heat acts, starch gelatinization and gluten coagulation occur almost instantly. Within a few minutes, the water evaporates so completely that the entire surface of the bread is covered with a strong, although still stretchable and elastic film. With the gradual penetration of heat into deeper layers, more and more new parts of the surface turn into such a viscous shell.
But at the same time, all the outer layers, as they become drier and cannot use the continuing flow of heat to evaporate water, heat up more and more, while changes occur that should be caused by the action of a higher temperature on starch and protein substances.

With regard to starch, we know that it, when heated to higher temperatures, passes into dextrins. During the baking process, the same dextrins are formed. It extends to all parts of the dough piece that are hot enough for these changes to occur, that is, to the entire upper shell. The dextrins in the oven are immediately dissolved and fixed in a thin layer on the surface. Thanks to this, the surface acquires its own gloss.

The transformation of gluten protein due to high temperature has not been chemically studied in more detail. The protein is colored, at first without any significant material changes, when heated, in an increasingly darker tone; if heated too much, nitrogen is lost due to the elimination of volatile nitrogenous compounds, and partial decomposition of the protein occurs.

Upon further heating, the outer layers of the dough lose so much water that they become a dense, no longer stretching mass, called a “crust.” Simultaneously with the transformation of starch into dextrin, the crust takes on a yellow (to brown) color. It becomes darker the longer the heat remains it gets stronger, along with dextrins, and more and more carbon-rich products such as caramel, known as color and a dark brown substance, then appear.

Finally, products of unknown composition are formed, which are colored the darker the stronger the heating, and then charring can occur if heated too much.

Schematically, it looks something like this:

Temperature
Processes in the test

30
Swelling, gas formation, enzymatic sugar formation.

45— 50°
Strengthening these processes. Killing of fermentative fungi.

50— 60°
Vigorous activity of enzymes. Carbon dioxide pressure. Beginning of gelatinization.

60— 80°
Starch gelatinization. Protein folding. Weakening and termination of enzyme activity.

100°
The formation of water vapor, its distribution throughout the crumb. Solidification of the water-releasing crust.

110—120°
Formation of dextrins (light, yellow dextrins).

130—140°
Formation of dextrins (brown dextrins).

140—150°
Formation of caramel (turning brown).

150—200°
Roasting products (dark brown).

Vyc. t
Coal formation (black porous mass),

The temperature of the crust should reach 180-200 ° C in a normally fired oven: We have already said that it is in some places or higher or lower. Accordingly, we will find the greatest change in the substance and thus a darker color on the lower part and on the upper crust of the loaf, while the weaker heating of the side walls (where only the formation of dextrins occurs) will be lighter.

The task of the baker is therefore to arrange the baking process in such a way, by regulating the heat and evaporation of the water in the oven, so that the crust is formed gradually, so that the transition of the dark layers into light breads occurs evenly.

The changes that undergo
when baking, the inner part of the dough, which forms the “crumb” of the bread. The oven heat does not penetrate quickly enough into the inside of the bread and the dry film that forms very quickly on the surface of the bread is such a poor conductor of heat that the temperature rise inside the bread slows down even more. knowledge of the temperature curve is necessary.Already in earlier experiments it was established that the temperature of the inside of bread does not exceed 100 ° C. How this temperature is reached during baking is shown by a resistance thermometer.