Information about bread

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1. GENERAL DESCRIPTION:

1.1 General Flowsheet of bread production

Figure 1: Production of bread.

1.2 Description of techniques, methods and equipment

(BAT for Food, Drink and Milk Industries, June 2005)

Bread is the product of baking a mixture of flour, water, salt, yeast and other ingredients. The basic process involves mixing of ingredients until the flour is converted into a stiff paste or dough, followed by baking the dough into a loaf.

;Breadmaking involves the following basic steps:

Mixing

1. To evenly distribute the various ingredients. 2. Allow the development of a protein (gluten) network to give the best bread possible. Each dough has an optimum mixing time, depending on the flour and mixing method used. Too much mixing produces a dough that is very extensible with reduced elastic properties. Undermixing may cause small unmixed patches which will remain unrisen in the bread. This will give a final loaf with a poor appearance inside.

Rising (fermentation)

Once the bread is mixed it is then left to rise (ferment).As fermentation takes place the dough slowly changes from a rough dense mass lacking extensibility and with poor gas holding properties, into a smooth, extensible dough with good gas holding properties.

The yeast cells grow, the gluten protein pieces stick together to form networks, and alcohol and carbon dioxide are formed from the breakdown of carbohydrates (starch, sugars) that are found naturally in the flour.

Kneading/moulding into loaf shapes

Any large gas holes that may have formed during rising are released by kneading. A more even distribution of both gas bubbles and temperature also results.The dough is then allowed to rise again and is kneaded if required by the particular production process being used.uring the final rising (proving) the dough again fills with more bubbles of gas, and once this has proceeded far enough the doughs are transferred to the oven for baking.

Baking

The baking process transforms an unpalatable dough into a light, readily digestible, porous flavourful product. The physical activities involved in this conversion are complex but the fundamentals of these are explained.

1. 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.

2. 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.

3. The oven heat changes liquids into gases by the process of evaporation and thus the alcohol produced evaporates.

4. 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 onwards 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.

Cooling – slicing and wrapping

In bakeries bread is cooled quickly when it leaves the oven. The crust temperature is over 200°C and the internal temperature of the crumb about 98°C. The loaf is full of saturated steam which also must be given time to evaporate. The whole loaf is cooled to about 35°C before slicing and wrapping can occur without damaging the loaf.A moist substance like bread loses heat through evaporation of water from its surface. The rate of evaporation is affected by air temperature and the movement of cool air around the loaf.In a bakery there are special cooling areas to ensure efficient cooling takes place before the bread is sliced and wrapped.

Different types exist, depending on the country

;France

80% of the total production is produced is small bakeries. Baguette is the most common eat type of bread.

;Germany

In Germany five principle types of bread are common:

1. Wheat bread (at least 90% wheat)

2. Mixed wheat-rye breads (min. 50% wheat)

3. Mixed wheat-rye breads (min. 50% rye)

4. Rye breads (at least 90% rye)

5. Bread specialties (by adding non- bread grains such as maize and rice or materials of animal origin such as butter, milk and yoghurt or by using special baking technique)

;United Kingdom

1. Sandwich bread

typical are a high volume soft texture, a fine porous crumb structure and long shelf live properties

2. Malt bread

a kind of sticky, sweet and dark bread

3. Rye bread

commonly a 50:50 mix of wheat flour and rye flour

The production mostly begins with mixing flour, water and other ingredients to form a dough, By incorporation of air good volume, structure and texture is achieved during baking.

Several methods for making bread exist:

• Straight dough process

All ingredients are added together at the start. Then the dough ferments for 2 or 3 hours and afterward it is divided into leaf sized pieces followed by forming them into balls. After a proof time of 10-20 min they are molded and panned.

• Sponge and dough process

The sponge is prepared from part of the flour (ca. 65%), water and yeast. It is just mixed to have an uniform mixture and is then allowed to ferment for 3 or 4 hours. Then the sponge is taken back to the mixer and is mixed with the rest of the ingredients. Then it is given a floor time of 15 min to relax.

• Sour dough

Dough containing a higher proportion of flour or meal requires more acidification. This is generally achieved by sour dough process. Various types of processes were designed to increase the growth of yeast and lactic acid bacteria to give the final dough proper acidity and dough consistency. The proof time for this kind of bread is long (several hours) and for rye bread acidification is required. After the bulk fermentation the dough is divided into loaf sized pieces. Then a floor time is given which allows the dough to relax. The molding process is essentially sheeting followed by curling, rolling and application of pressure. After being molded the dough is panned and is then ready for proofing. During this step the dough increases greatly in volume and can then being baked in the oven.

• Chorleywood process

This kind of process is mostly common in the UK. The mixing and development of dough take place in just one single step in the presence of an oxidising agent. High quality wheat flour is required with a protein content of about 12.5% dry matter together with a high level of starch damage and hence high water absorption. Oxidising improver, fat or emulsifier and extra water and yeast are mixed in at this stage. The whole process lasts between 2 and 5 minutes. All short- time systems require high levels of oxidants. The dough mixing take place with an intensive energy input, then the dough is transferred to a hopper which is sometimes sprayed with oil. It is divided and then allowed to rest followed by final moulding and placing into tins which were sprayed with oil before filling them. Then the dough ferments for a second time and may be cut for baking. Baking times, temperatures and temperature profiles vary largely depending on the type of bread.

The heat is transferred by direct or indirect heat to the loaf. The most common energy sources in baking industry are natural gas and electricity.

After cooling the bread is sliced before wrapping ready for distribution.

1.3 Temperature ranges and other parameters

Table 1: Parameters of UO in bread production, Literature: Heiss, R. [Hrsg.]: Lebensmitteltechnologie

The rule of thumb is:

For the production of 1,5 kilo rye bread approximately 1 kilo of wheat, 850 ml of water and 30 gram of salt are required.

The weight percent of wheat in the final product (bread) is about 65%.

Table 2: Baking times and temperatures, Literature: Hirschberg, H.G.: Handbuch Verfahrenstechnik und Anlagenbau, Chemie, Technik, Wirtschaftlichkeit

1.4 Benchmark data

Table 3: Energy consumption of different bakery products, Literature: Heiss, R. [Hrsg.]: Lebensmitteltechnologie

Table 4: Energy Input, Literature: Hirschberg, H.G.: Handbuch Verfahrenstechnik und Anlagenbau, Chemie, Technik, Wirtschaftlichkeit

Table 5: Energy Input during kneading, Literature: Hirschberg, H.G.: Handbuch Verfahrenstechnik und Anlagenbau, Chemie, Technik, Wirtschaftlichkeit

Table 6: Energy Consumption in BTU per pound of product, Literature: Adapted from Sikirica et al, 2003)

2.1 Preheating in Baking Oven

2.1.1Changes in Energy Supply for unique Technology

2.1.1.1 Existing Heat/Cool Technology

The oven is preheated with hot water

2.1.1.2Changes in Distribution of the Heat/Cool System

Water is replaced by Air

2.1.1.3 Optimisation of the Heat/Cool System

This preheating can be performed by The Air-cooled heat exchanger which is a device for rejecting heat from a fluid or gas directly to ambient air. When cooling both fluids and gases, there are two sources readily available,with a relatively low cost, to transfer heat to air and water.The obvious advantage of an air cooler is that it does not require water, which means that equipment requiring cooling need not be near a supply of cooling water. In addition, the problems associated with treatment and disposal of water have become more costly with government regulations and environmental concerns. The air-cooled heat exchanger provides a means of transferring the heat from the fluid or gas into ambient air, without environmental concerns, or without great ongoing cost. [Source: Basics of Air cooled Heat Exchangers: Amercool Manufacturing Inc.]

2.2 Mist Fermentation

2.2.1Changes in Energy Supply for unique Technology

2.2.1.1 Existing Heat/Cool Technology

No use of Ultrasonic smokescreen generator

2.2.1.2Changes in Distribution of the Heat/Cool System

2.2.1.3 Optimisation of the Heat/Cool System

Small droplets are created through ultrasound that produces a mist for the fermentation process.This results in improved heat conductivity of the end product without drying out too much.Energy saving during baking (energy saving 17%) Ultrasonic smokescreen generator during fermentation allows a 17% energy saving. Investment costs are between 4000 to 12000 Euros [ Source: Energy-saving mist technology available on industrial scale By Oliver Nieburg]

==2. Vacuum Baking == ONLY FOR BISCUITS

2.2.1Changes in Energy Supply for unique Technology

2.1.1.1 Existing Heat/Cool Technology

Conventional baking process was performed using an oven at 180, 190,200oC for different times up to 15 min.vacuum baking process was performed using a vacuum oven at 160, 180, 200 oC and at 500 mbar for different times up to 17 min.

2.1.1.2Changes in Distribution of the Heat/Cool System

2.1.1.3 Optimisation of the Heat/Cool System

vacuum baking allows production of biscuits with very low PC content linked to the lighter colour of the biscuit due to a lower degree of desired Maillard reaction which also results in different sensorial profiles.It is a new technology to produce biscuits with lower acrylamide levels as a result of the effect of lower temperaturesThe principle of vacuum baking was to decrease pressure in the oven,to decrease boiling point of water during baking. Baking under vacuum allowed us to decrease cooking temperature without retarding the drying process, because moisture evaporation was accelerated under vacuum. Reducing atmospheric pressure in the oven by half enables to decrease ,baking temperature by 20oC with approximately same drying rate.

Vacuum baking is expected to have up to 50% energy saving vs conventional oven Low pressure baking concept has been validated. First tests showed that an energy reduction by 50% can be expected meanwhile the moisture lost was reduced by at least 30% and the bread volume was increased by 20% vs reference.[Source:PROMETHEUS]

==2. Waste Heat recovery from biscuit oven stacks == ONLY FOR BISCUITS

2.2.1Changes in Energy Supply for unique Technology

2.1.1.1 Existing Heat/Cool Technology

2.1.1.2Changes in Distribution of the Heat/Cool System

2.1.1.3 Optimisation of the Heat/Cool System

Biscuit manufacturing involves high temperatures for baking .Various type of ovens are available for baking bakery products . Heat recovery can be done for biscuit oven which has 5 - 6 zones basically in indirect Oven .As temperatures are very high ( 400-500degc) on feed end these stacks are then joined to a common duct which collects heat from these stacks with help of blower and then these flue gases is passed onto the last zone which requires low temperature . This temperature is as low as 180- 200 deg c can be attained by circulating flue gases collected in common duct from these stacks .This eliminates need of one burner all together at coloring zone or last zone .Fuel is saved by implementing this kind of arrangement . 15 ltrs-20ltrs /hr can be saved.

2.1.3.1 Description of the Technology

2.1.3.2 Possible Energy Savings Reachable by those measures

2.1.3.3 Economic Evaluations

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