Tribology and making biscuits
R. David Whitby | TLT Worldwide March 2021
Commercial biscuit making even uses lubrication.
Biscuits are made with large scale commercial mixers, and their rotating bearings are lubricated with food-grade oils or greases.
All industries use lubricants, although many people are unaware of the many surprising ways in which lubricants and lubrication are used. Take commercial biscuit making, for example.
A biscuit is a flour-based baked food product. Outside North America, a biscuit is typically hard, flat and unleavened. In North America, it is typically a soft, leavened quick bread. In the U.S., biscuits and cookies are often grouped together, while in the UK, a cookie is just another type of biscuit, although larger and less hard.
The meaning of the word biscuit (outside North America) is “twice-cooked.” In Latin,
bis means
twice, and
coctus means
to cook. In the original method of cooking in the 16th and later centuries, biscuits were returned to the oven after the initial period of baking in order to become dry or crisp. Two biscuits might be pressed together with a filling, or a biscuit could be topped with icing or chocolate. In the U.S., cookies and biscuits are cooked only once. In both countries, cookies are made using either baking soda or baking powder, so are leavened.
The commercial methods of making biscuits and cookies are quite similar. The first step in both processes is to make the dough. For European biscuits, flour, water and other ingredients such as sugar, milk, oil and/or eggs are mixed together. For North American biscuits, flour, water and yeast are mixed together and allowed to ferment for an appropriate length of time, according to the specific recipe. In both cases, large scale commercial mixers are usually made of stainless steel, and their rotating bearings are lubricated with food-grade oils or greases.
The next step differs slightly. With European biscuits, the dough is rolled onto a flat, moving conveyor, and a rotary cutting machine continuously cuts out the required shapes. The number of shapes cut per rotation depends on the width of the conveyor and the size of the biscuit. The conveyor’s rollers and the cutting machine’s bearings are again lubricated with food-grade lubricants. The excess dough is recovered from the end of the conveyor and returned to the roller. The individual uncooked biscuits slide onto a second conveyor unit, ready to be baked. With North American biscuits, the dough is fed into small circular pans, much like the larger pans used to bake bread, also on a moving conveyor.
The biscuits are then fed on the conveyor into a tunnel baking oven, which has a long furnace body heated either by gas or electricity. For European biscuits, modern ovens have two sections: the first for cooking and the second for drying. For North American biscuits, the whole oven is just for baking. The oven heating system, transmission system, ventilation and moisture control are computer controlled. Again, the conveyor rollers are lubricated but with a high temperature food-grade lubricant.
The biscuits must be cooled to 38-40 C before they can be packaged. European biscuits need to have a moisture content below 6.5% to achieve optimum shelf life. The cooling conveyor has either a single or two-tier arrangement, depending on factory layout. A two-tier system is often used when it is desirable or necessary to turn biscuits over during cooling. This avoids uneven moisture distribution, which leads to cracking of biscuits. North American biscuits need to be removed from their pans, usually by flipping them over.
It is important that the biscuits don’t stick to the cooling conveyor. This is achieved either by spraying a thin film of vegetable oil onto the conveyor or using a conveyor that has closely spaced tiny holes through which air is blown to gently lift the biscuits from the surface. This type of conveyor also is used to control the rate of cooling.
Following cooling, a servo-controlled system guides the biscuits into a biscuit stacking and packaging machine. Servo-control is used to monitor the position of the biscuits on the cooling conveyor, a channelling board, lane distributor, lane reducer, lane multiplier, flip stacker and stacking machine. This ensures that a widely spaced, “nested” pattern of biscuits converges efficiently into a series of closely spaced individual lanes of product. A stacking unit accepts biscuits in a flat configuration from the channelling board and converts them to an “on-edge” formation, and continuously builds “slugs” of biscuits. These are transferred to the infeed of a wrapper or cream sandwiching machine.
David Whitby is chief executive of Pathmaster Marketing Ltd. in Surrey, England. You can reach him at pathmaster.marketing@yahoo.co.uk.