Bread is one of the most consumed items throughout the world. Whether they are flatbreads or risen breads, breads have been a big part of humans‘ diets for thousands of years. They are thought to be the first processed food humans ever created. Modern bread making has taken advantage of the many engineering processes available today.
Bread is composed of a few simple ingredients: flour, water, and yeast, with most breads also including salt, sugar, and other additives. Before bread can be made each ingredient must go through its individual preparation processes.
Flour is the crushed form of cereal grains. The most common flour used in the production of bread is wheat flour, but flour can also be made from other grains such as rye, barley, and rice.
The wheat grain, the seed of the wheat plant, is composed of three parts: the outer husk called the bran; the germ, which contains the structure of the new plant if it were to be allowed to grow; and the endosperm, which is rich in starch and proteins integral to the bread-making process. For white bread, only the endosperm is desired, whereas whole wheat flour uses all the components of the grain, hence the term whole wheat.
Before the grain can be milled it must be at the proper moisture content for the desired milling. This is achieved through storing in a dry environment to allow the grains to dry, checking the moisture content periodically until the desired moisture content is achieved.
The grain is milled using roller mills to crush the grain and separate the endosperm from the bran and germ. There is usually a sequence of roller mills in succession which produce gradually smaller particle sizes, with sifters in between the mills to sift out the bran and germ, the process is shown in the diagram below. If white flour is desired, this powder of endosperm is able to be packaged, and if whole wheat is desired the germ and bran are crushed as well and added to the powdered endosperm.
Yeast is a single-celled microorganism used as the leavening agent in most breads. Yeast is grown by placing a starting colony in a large vat of growth medium, such as sugar and water, and allowing the yeast to reproduce. The yeast eventually precipitates out of the solution, forming a layer of yeast at the bottom of the vat, which can be separated from the liquid. This is then packaged and shipped to the bakeries. There is not much preparation required for yeast, as it can be added directly to the mixture of other ingredients. Yeast can also be kept viable for a few months under cool storage conditions.
Water is a very important ingredient in bread, as it accounts for about 40% of the dough mass. The water used in bread-making must be potable, so usually some form of purification such as membrane filters or adsorbers is used to achieve the desired purity.
The production of bread consists of seven steps: mixing of ingredients, fermentation, kneading, baking, cooling, slicing, and packaging.
Mixing of Ingredients
The flour and other dry ingredients, such as sugar, salt, and other additives, are added to a mixer, followed by the water and yeast. The ingredients are mixed until a viscoelastic dough is formed due to water binding the wheat proteins gliadin and glutenin, which form gluten. Gluten gives the dough its elasticity and structure. This allows the dough to retain carbon dioxide bubbles during fermentation, giving the dough an airy light texture.
Fermentation is the process by which yeast consumes sugars and produces ethanol and carbon dioxide (CO2). The purpose of this step is to aerate the dough and allow it to rise so that the bread will turn out airy and not dense. If a flatbread is desired the fermentation steps are left out and the dough can move straight to the kneading and baking step. There are three options for the first fermentation.
The first and most traditional form of fermentation is batch fermentation, where the dough is placed in large vats. The vats are then taken to a room held at a specific temperature, usually between 21-37 ℃ ( 70-100 ℉ ) for ideal fermentation. Then the dough is left there for up to an hour or more until the dough has doubled in size from the produced gas. This process takes the longest of the different types of fermentation, but specialists contend it produces the best flavor.
Chorleywood Bread Process
This process is relatively new, developed in 1961 by the British Baking Industries Research Association. It uses a high-powered, high RPM mixer to mix the dough to such a fine degree that the first fermentation is not even necessary. The thorough mixing achieves most of the yeast’s job during fermentation by aerating the dough, which helps produce risen bread. The high-powered mixers also produce a significant amount of heat due to the friction generated by the high speeds. This excess heat actually helps the yeast to produce carbon dioxide.
Sponge and Dough Method
This method is similar to bulk fermentation, but instead of fermenting the entire batch of dough, a much smaller amount called the sponge is fermented and then added to the bulk dough. The sponge is a less dense version of the dough with a higher water to flour ratio, and it usually has more sugar as well. The sponge is allowed to ferment for up to five hours. The fermentation of the sponge activates the yeast and initiates their reproduction stages so that a large volume of yeast are ready to ferment the bulk dough. This sponge is then added to the bulk of the dough, which decreases the amount of time that the full volume of dough needs to sit and ferment. This method is useful because a large amount of sponge can be made ahead of time and then small amounts of this sponge can be added to large batches of dough to decrease total fermentation times.
After fermentation, the dough is separated into sections that will eventually be individual loaves. These are put on a conveyor that will take them through the rest of the bread-making process. The dough is then put through a batch kneader. Kneading the dough further develops gluten and forms a smooth surface structure that eventually forms the crust once baked. After the dough has been kneaded for a short period, the dough balls are allowed to rise a second time through the proofing stage, a short rest period between kneading and baking, until it reaches the desired volume, at which point it is ready for baking.
The dough is then fed via conveyor to an oven for baking. The oven is set between 180-230 ℃ (350-450 ℉) depending on the different characteristics desired in the bread and what additives were added. The bread rises during this stage as well due to the production of carbon dioxide by the yeast. The starches, proteins, and water all bind together during this stage, resulting in the familiar feel and taste of bread. The baking process can take anywhere from 15 minutes to over an hour depending on the desired final bread characteristics and initial dough qualities.
The bread is then either cooled on a conveyor placed on cooling racks until it reaches room temperature. As the bread cools, its structure becomes firm. Moisture content must be monitored closely at this step because the bread is prone to absorbing large amounts of moisture as it cools. Too much moisture could lead to mold formation and affect the texture of the bread. The humidity levels in the bakery are monitored carefully, using a humidity measurement device, to ensure this does not happen.
The bread is then sent to a slicer that has serrated vertical blades that slice the bread into a specified number of pieces. These blades must be replaced often and sharpened to ensure the bread does not get damaged during this process.
The cut and cooled bread is then sent to a packaging machine that slips a plastic bag over the bread and then seals the bag, usually with a zip tie. This step can also be done manually.
The quality control of bread is a process that spans all the production stages. Ingredient ratios are precisely controlled, temperatures of the various processes are held in their optimum ranges, and the moisture of the final loaf must be tested to ensure it’s at the desired level.
Some of the defects that can occur in bread are excessive gas production in the dough or excessive gas retention. The reverse could also be a problem, not enough gas production or retention. The causes can be from too much or too little yeast, too high or low temperature, or too much time or not enough time in the fermentation and proofing step. These problems can be resolved by strictly monitoring temperatures and times in each stage. Spoiling such as mold must be controlled by keeping the moisture content at the desired level and packaging as soon as possible after the cooling stage.
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- Daniel Watza