Bread freezing water

Fig. 15.53. Decrease in freezing water in the storage of white bread. The bread was stored at room temperature encapsulated to prevent drying (according to Slade, Levine, 1991)...

This recrystallisation releases water. This is probably why, although deep freezing prevents starch retrogradation, refrigeration at temperatures above zero causes bread to stale faster than storage at ambient temperature. 

The caloric behavior of water has been studied by Riedel (1959), who found that water in bread did not freeze at all when moisture content was below 18 percent (Figure 1-16). With this method it was possible to determine the nonffeezable water. For bread, the value was 0.30 g per g dry matter,... 

Figure 1-16 Specific Heat of Bread of Different Water Contents (Indicated as %) as a Function of Temperature. Source. From L. Riedel, Calorimetric Studies of the Freezing of White Bread and Other Flour Products, Kaltetechn, Vol. 11, pp. 41—46, 1959.

Crumb firming is inversely proportional to specific volume of bread. Rate of crumb firming is at a maximum near (but not at) the freezing point of water and decreases as temperature is increased or decreased on either side. 

Staling of white-bread crumb begins with the formation of crystalline structures in amylopectin. The endotherm peak at 60 °C appears again in the thermogram of stored white bread (Fig. 15.52). A state of order arises which corresponds to that of B starch (cf. 4.4.4.14.2) and binds up to 27% of crystal water, which is withdrawn from amorphous starch and proteins. The crumb loses its elasticity and becomes stale. On storage of white bread, the amount of water that can freeze decreases corresponding to the conversion to non-freezing crystal water (Fig. 15.53). 

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