Cereal chemist George Lookhart at the chief government science agency, the Agricultural Research Service, is trying to determine how and why staling happens, something that scientists have been struggling to explain for more than 150 years.
"At the heart of the staling process is moisture movement throughout the tortilla via the protein matrix and starch molecules," said the chemist.
Lookhart and his colleagues at the Hard Winter Wheat Quality Laboratory, in Manhattan, Kansas, have developed a laboratory-scale method that can predict whether a flour type will yield the perfect tortilla - about 2 millimeters thick and evenly opaque, with ample diametre and at least a 3 week shelf life, a boost for the $5 billion tortilla industry.
The new tortilla test could lead to development of wheat varieties that have just the right gluten strength and protein makeup to be grown exclusively for tortilla production.
"With just a small amount of flour from early-generation wheat plants," said the scientist, "the test allows breeders to use small-scale, lab-produced tortillas to compare and distinguish tortilla quality in wheat breeding Lookhart, bases a tortilla's quality partly on how strips of the flat breads perform when being stretched across a special plate. He then measures the forces involved in this stress test and determines the level at which they cause the tortilla strips to break.
A wheat tortilla's tenacity is largely dependent on the kinds of proteins that are found in its flour. Known as gluten, the proteins can impart strength to a tortilla, allowing it to endure the stress of being rolled up without cracking.
But when flour from a particular wheat variety has excessively strong gluten, says Lookhart, the tortilla made from it will have too much 'spring' - causing it to shrink in and lose valuable surface area when the dough is released from the tortilla press. Finding the right balance of proteins is an important part of the wheat-breeding research.
The US researcher is now planning to examine the chemistry of the staling process in other grains, such as sorghum.