The following block diagram shows the production steps in bread processing using different dough systems.
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The style and type of bread dictates the dough system to use as well as the processing conditions during mixing, makeup and baking. A baker would not like to produce ciabatta with a close crumb structure, or to produce a loaf of white pan bread with an open crumb structure and texture like a ciabatta.
All steps in bread processing are important for a successful operation, but most bakers would agree that the three truly vital process steps are mixing, fermentation and baking. They are commonly described as the heart and cornerstone of breadmaking operation and can also determine the finished product characteristics, both internally and externally.
The objective is the blending and hydration of dry ingredients, air incorporation and gluten development for optimum dough handling properties. Variables to monitor and control include mixing time, energy input, dough temperature:
The objective is yeast growth, production of CO2, ethanol and organic acids, development of flavors and aromas, and modification of dough handling properties. Variables to monitor and control include fermentation time, temperature, titratable acidity (TTA), pH, microbial count:
Makeup stage mainly encompasses four operations:
The divider cuts bulk dough into single pieces of proper weight (with as little stress exerted on dough as possible) so that these can be rounded and rested prior to taking their final shape. The divider must process the entire dough load quickly to prevent excessive gassing that creates scaling errors.
The sheeter and moulder encompass the sheeting stage, curling chain, pressure board, and guide bars. These influence the gas bubble structure, shape and length of the dough piece to place in the pan.The moulder should be adjusted to achieve the desired shape with a minimum amount of pressure and stress on the dough to avoid damaging cell structure obtained during mixing and fermentation.
The objective is to convert raw dough into bread, set structure of product, crust and crumb formation, kill-step and shelf-life extension. Variables to monitor and control include temperature, time (governed in continuous ovens by conveying speed). Other relevant variables include heat flux (burners), humidity (dampers) and air velocity or flow.
The baking process transforms an unpalatable dough into a light, readily digestible, porous flavourful product.
As the intense oven heat penetrates the dough the gases inside the dough expand, rapidly increasing the size of the dough. This is called &#;ovenspring&#; and is caused by a series of reactions: Gas + heat = increased volume or increased pressure. Gas pressure inside the thousands of tiny gas cells increases with the heat and the cells become bigger.
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A considerable proportion of the carbon dioxide produced by the yeast is present in solution in the dough. As the dough temperature rises to about 40°C, carbon dioxide held in solution turns into a gas, and moves into existing gas cells. This expands these cells and overall the solubility of the gases is reduced.
The oven heat changes liquids into gases by the process of evaporation and thus the alcohol produced evaporates.
Heat also has an effect on the rate of yeast activity. As the temperature rises the rate of fermentation increases, and so does the production of gas cells, until the dough reaches the temperature at which yeast dies (approximately 46°C).
From about 60°C, stabilisation of the crumb begins. Starch granules swell at about 60°C, and in the presence of water released from the gluten, the outer wall of the starch granule cell bursts and the starch inside forms a thick gel-like paste, that helps form the structure of the dough.
From 74°C upwards the gluten strands surrounding the individual gas cells are transformed into the semi-rigid structure commonly associated with bread crumb strength.
The natural enzymes present in the dough die at different temperatures during baking. One important enzyme, alpha-amylase, the enzyme which breaks starch into sugars, keeps on performing its job until the dough reaches about 75°C.
During baking the yeast dies at 46°C, and so does not use the extra sugars produced between 46-75°C for food. These sugars are then available to sweeten the breadcrumb and produce the attractive brown crust colour.
As baking continues, the internal loaf temperature increases to reach approximately 98°C. The loaf is not completely baked until this internal temperature is reached. Weight is lost by evaporation of moisture and alcohol from the crust and interior of the loaf. Steam is produced because the loaf surface reaches 100°C+. As the moisture is driven off, the crust heats up and eventually reaches the same temperature as the oven.
Sugars and other products, some formed by breakdown of some of the proteins present, blend to form the attractive colour of the crust. These are known as &#;browning&#; reactions, and occur at a very fast rate above 160°C. They are the principal causes of the crust colour formation.
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