Paper No. 09 Paper Title: Bakery and Confectionery Technology Module 6: Overview of bakery machinery: mixers, forming machines and ovens. Introduction Bakery units can be classified as manual, semi-automatic and fully automatic. At small scale, mixing and dough preparation is done manually. Such units use electric or wood fired brick oven for baking. Medium and large bakery units are relying extensively on bakery machinery and automatic systems. Mechanization systems are required in a bakery plant because of following reasons: Enables large scale production and thus comes economy of scale For continuous operation To make different products on the same production line. Saves time by rapid processing Hygienic consideration Minimise manual labour and material handling To get consistent product quality. Automatic weighing and metering for formulation. Better control over the production. By using sensors and electronic controls, entire bakery plant can be centrally controlled by a computer system. 1.0 Mixers Mixing is a term used to describe combined process of stirring, beating and blending. Proper mixing of ingredients is a prerequisite for good quality bakery product. The objective of mixing are: Transfer of energy to the dough during mixing helps to increase gas retention and increase bread volume. Uniform distribution of ingredients and optimum blending with water to form coherent dough. To achieve desirable dough properties which are strongly influenced by mixing. Transfer of energy to the mix to develop gluten network. This transfer of energy depends on the time of mixing, geometry of mixer tool and bowl. Minimum loss of the additives Incorporation of air into the mix Development or prevention of gluten network 2.0 Types of mixers 1
Batch mixer a. Vertical mixers: Mixing tools or beaters are mounted on a vertical shaft. The shaft not only rotates about its own axis but also has a planetary circular motion inside the mixing bowl (Fig. 1). In few dough mixers, there may be two or three intermeshing beaters and in such cases beaters rotate on fixed shaft. The mixing bowl may be detachable with provision to lower the mixing tool into the bowl or to lift the bowl to the level of the beater (Fig. 2 a & b). In few models the head consisting of drive, shaft and beater is tilted back to remove the bowl (Fig. 2 c). Fixed type mixers have provision to tilt the bowl and remove the dough (Fig. 2 d). Fig.1 Planetary circular motion of the mixing tool (a) (b) (c) (d) Fig.2 Different models of dough mixers The beaters are available in various geometries, each having some specific application (Fig. 3). The mixer may be of fixed speed type or of variable speed. 2
Fig.3 Different geometries of mixer tool/beater b. Horizontal mixers: Mixing tools or beaters are mounted on a horizontal shaft (Fig. 4). Such mixers are used for high speed operations. There are two basic models of horizontal mixer. First, in which bowl is fixed and the beater rotates. In the second type the bowl rotates and the beater is fixed. Bowl has a door for loading of ingredients and unloading of dough. 3.0 Forming machines The various principles for forming are: 3.1 Sheeting, gauging and cutting 3.2 Rotary moulding 3.3 Extruding Fig. 4 Horizontal mixer 3.1 Sheeting, gauging and cutting i. Sheeter: Sheeter comprise of hopper and two or three rollers. Dough is fed to the hopper and it is pressed by the rollers into rectangular sheet (Fig 5). The functions of a sheeter are as follows: To form sheet of uniform thickness and width that can be cut into pieces. To compress the dough into compact sheet and remove holes. For smoothening uneven surface. To remove entrapped air. 3
After cutting leftover material is fed back to the sheeter. The scrap material gets mixed with the dough in the sheeter hopper. The wastage is reduced is in this way. Fig. 5. Dough sheeter ii. Gauge roll unit: It is used to reduce dough sheet to required thickness. Gauging unit is installed after the dough sheeter. The unit consists of two or three sets of solid rolls to press the sheet and reduce the thickness (Fig. 6). Multiple roller gauging units are used to obtain thinner dough sheet. Fig. 6 Gauge roll unit iii. Cutting machine: The dough sheet is cut into pieces of desirable shape and size using a cutting machine. Cutting machines are of two types: a. Reciprocating cutter: The reciprocating head consists of cutter and ejector plate. As the dough sheet moves on the cutting web, ejector is pushed inward and cutter outward. The sharp edge of cutter cuts the sheet into definite size. The cutter moves up to its original position and the ejector is released. Ejector pushes and holds the pieces firmly to the conveyor or cutting web. The pieces stick to cutting web so that it is not lifted by the reciprocating head. The timing of reciprocation head and conveyor speed is synchronized to get definite rows of dough pieces. The ejector plate may have decorative pattern or embossing. b. Rotary Cutter: The system consists of dockering, cutting and anvil rolls (Fig. 7). The cutting edge, pattern or embossing is mounted on the cutting roll (Fig. 8, 9). 4
Dockering roll Cutting roll Cutting web Anvil roll Fig. 7 Rotary Cutter Fig. 8. Cutting roll Round cutter Triangle cutter Rectangular cutter Hex scrapless cutter Hex scrapless cutter Donut cutter Fig. 9 Machine cutter pattern 5
3.2 Rotary moulding Rotary moulder unit consists of a. hopper, b. moulding roll, c. Pressing or forcing roll, d. Rubber extraction roll e. Extraction web, f. Scraping knife. Rotary moulders are widely used to form biscuit pieces from short dough. Moulding roll has grooves/moulds in which the dough is filled from the hopper. The mould can be of different shapes circular, rectangular, square etc. The pressing roll ensures that the moulds are completely filled. Knife placed over the moulding roll cuts the filled dough and scrapes the excess material. It also gives a smooth surface to the dough piece. The moulded pieces are picked up by the extraction web moving on the rubber roll. Hopper Pressing roll Moulding roll Knife Knife Rubber roll Fig. 10 Arrangement of rotary moulder 3.3 Extruding Two or more extruding rolls are used to press the dough into a narrow pressure duct. Dough is extruded into a definite shape through the die located at the bottom of pressure duct. A reciprocating wire cutting mechanism cuts the extruded dough forming separate pieces. Rotating knifes with sharp edge are also used for cutting. In continuous extruders, dough is forced continuously into the pressure duct and pieces are cut simultaneously by the wire cutter. In some extruders, pressing of dough and cutting is done alternately. Extruders may have single head or more than two heads for forming multiple rows of dough pieces. 6
Hopper Extruding roll Wire cutter Die Fig. 11 Wire cut extruder 4.0 Baking Ovens The oven may be heated by steam, oil, gas, wood, coal or electricity. The mode of heating may be conduction, convection or radiation. 4.1 Rotary Rack Oven The oven consists of a rotating rack with provision to load trolley (Fig. 12). Each trolley will have 10-15 shelves to hold product trays. Product is heated uniformly on the rotating rack (Fig. 13). The mode of heating is forced convection and maximum baking temperature achieved is around 300 o C. Rotary rack oven can be further classified as: Fixed Trolley Oven Single Trolley Oven Double Trolley Oven Multi Trolley Oven 4.2 Deck oven Deck ovens are used on small scale. Deck oven have number of heating chambers which are arranged one over the other (Fig. 14). Mode of heating is conduction. The heating chambers have individual controls to bake multiple products at a time. 4.3 Tunnel oven Tunnel ovens are used for continuous baking operation. The product moves over a steel band or wire mesh conveyor. The conveyor speed determines the residence time of product in the oven. The oven temperature and conveyor speed is set such that product is completely baked before leaving the tunnel. Tunnel is divided into two, three or more temperature zones. Each zone has separate temperature controller. 7
Fig. 12. Rotary rack oven Fig. 12. Rotating rack to load trolly 8
Fig. 13 Deck oven Fig. 14 Tunnel oven References Baked Products: Science, Technology and Practice. Stanley P. Cauvain and Linda S. Young. Blackwell Publishing, U.K. The Science of Bakery Products. Ed. W. P. Edwards. The Royal Society of Chemistry, U.K. Technology of Biscuits, Crackers and Cookies. Duncan Manley. Woodhead Publishing Ltd, U.K. 9