The fireless cooker is particularly desirable in the cooking of cereals.
In experiments made with rolled oats at the Minnesota Experiment Station, it appeared that cooking (four hours) did not make the starch much more soluble. However, it so changed the physical structure of the grains that a given amount of digestive ferment could render much more of it soluble in a given time than when it was cooked for only half an hour.
On the basis of the results obtained, the difficulty commonly experienced in digesting imperfectly cooked oatmeal was attributed to the large amounts of glutinous material which surrounds the starch grains and prevent their disintegration. When thoroughly cooked the protecting action of the mucilaginous protein is overcome, and the compound starch granules are sufficiently disintegrated to allow the digestive juices to act. In other words the increased digestibility of the thoroughly cooked cereal is supposed to be largely due to a physical change in the carbohydrates, which renders them more susceptible to the action of digestive juices.
Pastry. Pastry is usually difficult of digestion because the fat it contains interferes with the proper solution of the starch. The objectionable features apply to such pastry as is made by rubbing fat into flour, as in pie crust, crust for meat pies, apple dumplings, etc. It does not apply to most puddings. Butter or fat is used in cakes, cookies, etc., but it is not rubbed into the flour; it is mixed with sugar and eggs which hold it in suspension until the flour is acted on by the liquids.
The coating of the starch granules with fat prevents them from coming in contact with liquids. The fat does not furnish sufficient water to enable the cells to swell and dissolve the cell wall and so coats the starch granules as to prevent them from absorbing water in mixing, or saliva in mastication. This coating of fat is not removed until late in the process of digestion, or until the food reaches the intestines.
The same objection applies to rich gravies, unless the flour is dissolved in water and heated before being mixed with the fats.
Pastry and biscuits require a somewhat hotter temperature than bread, because the process of cooking consumes less time.
Cooking of Vegetables
Since the root vegetables contain a large proportion of carbohydrates, they should be well cooked, in order that the crude fiber may be broken and the cells fully dissolved. Most vegetables are unpalatable and indigestible unless, by the cooking process, the starch granules are broken.