ABSTRACT
Commercial low-moisture baked goods, such as cookies, crackers, and hard pretzels, derive their characteristic textural crispness from the glassy solid state of their crumb structures (1–4). In polymer science terms, products of this class can be described as rigid foams consisting of air cells surrounded by a glassy matrix with “fillers,” or discontinuous inclusions. The matrix of a crisp cookie is a continuous sucrose-water glass with embedded ungelatinized starch granules, undeveloped gluten, and fat. Similarly, the matrix of a cracker or pretzel is a continuous glassy network of (partially) gelatinized starch, (partially) developed gluten, amorphous sucrose, and included fat. To achieve the kinetically metastable state of a glass, such products are deliberately formulated and processed so that the possibility for glass-to-rubber transitions within the matrix is minimized; i.e., the glass transition temperature (Tg ) is brought well above ambient temperature. Thus, variations in the crumb matrix—and perceived crispness—of these products are critically dependent on formulation, processing, and storage. For example, commercial cookies formulated with bread flour in place of soft wheat flour (the standard cookie formula ingredient) are typically hard or tough rather than crisp, a sensory difference traceable to the effect on Tg of high levels of damaged starch and pentosans typically found in bread flours (2, 3, 5). In regard to processing, as will be discussed in detail in this chapter, cracker and pretzel matrices can vary considerably, depending on the extent of starch gelatinization occurring 38in the preparation and baking of doughs. Storage conditions play a profound role in baked-goods crispness, because, as many have documented, the matrix is highly sensitive to absorbed moisture (see, e.g., Ref. 6). Since crispness is perhaps the most important sensory attribute of these products (7), the technologist must pay special attention to textural properties, in efforts to create new varieties or to improve the quality of existing varieties.
