Proving, baking and cooling

Abstract

Proving, baking and cooling are the stages of breadmaking that convert a fermenting dough into a stable product ready for consumption. There is evidence that leavened products were made in Egypt around 2000 bc and unleavened bread has been made since prehistoric times. The three operations-proving, baking and cooling-have been essentially the same ever since, relying on the properties of the raw materials and the way they behave when heated to produce a staple product that is both nutritious and good to eat. How the process was discovered we shall never know in detail but the huge variety of leavened bread products eaten across the world today all rely on the same basic principles. Proving, or proofing, allows time under favourable conditions for the yeast and enzymes in the flour to be active. Then, during baking, the rate of heat transfer is increased so that the outside of the loaf dries to a crust, and inside, the starch swells and the protein coagulates. Cooling reverses the direction of heat transfer and aims to produce loaves that are ready for wrapping, often with slicing as an intermediate operation. A typical timescale, with process conditions and their effect on loaf core temperature, is shown in Figure 5.1. Like many other processes in the food and drink industries, the details of the physical mechanisms and chemical changes occurring inside the dough during its various processing stages are extremely complex and only comparatively recently has it been possible to argue that breadmaking has become more of a science than an art. Since the mid-1950s, as more sophisticated measurement and microscopic techniques have been developed, understanding of the changes that occur during baking has advanced dramatically, increasing many-fold the resources available to the baker, particularly in ingredients, where flours, enzymes and special yeasts can be obtained, all tailored for specific purposes (Chapter 3). The ready availability of significant computing power means that dynamic models can now be constructed for the heat and mass transfer during baking, and computational fluid dynamics (CFD) can be used to visualize the air flows and heat transfer both in the processing chamber and also around and within (fiqure persented) the product. A plot of air velocity vectors in an oven chamber with a blowing nozzle, strip burners and an extraction point is shown in Figure 5.2. The application of imaging techniques has now extended to the use of X-ray tomography which has enabled the dynamic development of the internal processes which occur during proving and baking to be visualized (Whitworth and Alava, 1999; Cauvain, 2004). A better understanding of these heat transfer mechanisms has not led to any breakthrough in the design of the equipment to prove, bake and cool bread. The basic designs are well established and have developed in an evolutionary fashion, mainly to support increases in output and improvements in consistency and reliability. Every country has traditional breads, for some of which quite special baking conditions are required, but as a popular product spreads around the world, there is a tendency for its characteristics to change slightly to conform to the requirements of high-volume production on modern equipment. This tendency towards standardization makes it legitimate for this chapter to assume that the bread is being baked in tins or pans, as the processes used are substantially the same as for other specialty breads that may be proved and baked on flat plates. Figure 5.3 illustrates a variety of popular bread products and the choice of the range of products to be made, and their characteristics will determine how the plant is configured and adjusted. Some important considerations are as follows: What are the required crust and crumb properties? Is the surface to be glossy?(fiqure presented) Does the loaf have to be sliced? What must the final moisture content be to meet the yield target or legislative requirements? All these properties can be manipulated by changing the heat transfer programme, although they are not, of course, independent of the recipe formulation and mixing regime. This chapter does not contain any formulae, but attempts to explain qualitatively the mechanisms at work, in the belief that an understanding of what is happening during the later stages of the breadmaking process will be of more use in achieving the required product characteristics and in overcoming quality problems than will a list of specific instructions or pages of photographs of defective loaves. The properties of air and water mixtures are fundamental to the understanding of proving, baking and cooling, so a short refresher course on psychrometry has been included after this introduction. Production bakers will also be interested in production costs and in maintaining the performance of their heat transfer equipment, and some routine procedures are suggested to help them to monitor the state of the plant. (fiqure presented) Trends in equipment design are also indicated in each section and the promise of emerging technologies is discussed. © 2007 Springer Science+Business Media, LLC.