Starch occurs in the form of granules. See Fig. 39. In boiling water, the granule expands and finally bursts, and frees the content, the pure starch, and the whole mass thickens.

Boiled with an acid the starch is changed to dextrin, a sub-stance resembling a gum, and the mixture becomes thin; and this process continued changes the dextrin to dextrose.

With intense "dry" heat, as in toasting, the granule expands and opens, and the contents change to dextrin. Continued heat reduces the starch to pure carbon. The brown color and pleasant flavor in toast are a stage on the road to carbon.