The "Pyler says" series explores excerpts from Baking Science & Technology, a textbook that teaches readers a range of baking and equipment concepts. The following passage is from From Chapter 9: Mixing and Forming Equipment — Liquid Ingredient Storage and Handling.
Except for fats whose plastic character is essential to their proper functioning — such as shortenings used in some cakes, in icings and pie crusts and as roll-in fat, as well as water-fat emulsions such as margarine — all shortenings are suitable for bulk handling as long as their use volume is sufficiently high to justify the necessary capital investment for the required handling equipment. These would include the frying fats, bread shortenings and all fluid shortenings.
Bulk fat or oil deliveries are made either in tank trucks of 30,000- to 45,000-lb (4,000- to 6,000-gal) capacity or in rail tank cars that can carry from about 60,000 to 150,000 lb (8,000 to 20,000 gal). The delivery tanks are generally unloaded through either 3- or 4-in. flexible hoses provided with quick couplers and some straining or filtering device. A positive displacement pump is normally used for unloading and should have a rated capacity of 100 gal per minute so that it will empty a 60,000-lb tank car in about 2 hours. A 100-mesh screen should be installed ahead of the pump to remove any foreign debris.
In-plant holding tanks for bulk shortening can be manufactured from any of several materials such as stainless steel or stainless-clad steel, carbon steel, aluminum or reinforced polyester fiberglass. Their configuration is generally dictated by the available storage area: Low ceilings call for horizontal tanks, whereas vertical tanks are in order where the floor space is limited. Bronze, copper, brass should never be considered because they act as a catalyst for oxidation, which creates rancidity in the fats and oils.
The tanks should be cylindrical in shape using welded construction, with dished heads to ensure complete draining of the fat and be provided with the appropriate openings: two manholes, one each near the top and bottom of the tank, inlet and outlet openings, and openings for venting and for the heating coil, agitator and thermostat installations. Horizontal tanks may have either dished or flat ends, and they should be sloped at a rate of 1 in. per 10 ft toward the discharge end to ensure adequate draining. Rectangular tanks are inadvisable because their corners present cleaning problems.
Tank capacities should be large enough so each will hold at least one full truck tank load and two storage tanks accommodate a full rail tank load. The inlet line should extend to within a few inches of the tank bottom to minimize aeration of the liquid fat during filling and recirculation. Inventory control is provided either by an electronic load cell or some kind of level indicating device such as a sight gauge made from clear plastic tubing or a float gauge that calibrates the depth of the tank in terms of weight or volume of its contents. Of these, the load cell is not only the most reliable but also provides a perpetual inventory of the tank contents.
In order to keep shortening, other than the fluid type, in a melted or liquid state, its temperature must be maintained at least 6 C° (10 F°) above its melting point to maintain stability but allow the material to be pumped. Various means may be employed to achieve this purpose. For example, heating coils may be installed in the tank through which hot water or low-pressure steam is circulated, or electric immersion heaters may be used. When such internal heating methods are applied, it is advisable to insulate the tanks to minimize heat loss and prevent localized chilling. The heating coils are preferably situated about 4 in. above the tank bottom so that they will always be immersed in the liquid fat and will also promote maximum circulation by convection. Localized overheating must be guarded against because it will lead to quality deterioration of the fat.
Other approaches include equipping the tanks with external heating jackets or locating the tanks in so-called “hot rooms,” with the heat in both instances being applied externally to the shortening. Fats that solidify at ambient temperature require heating be provided for the lines leading from the storage tank to the pump and subsequent use points by tracing them with either a steam line or an electrical heating tape and by insulating them. With fluid shortenings, narrow temperature control is far less critical because these products retain their fluid state at temperatures as low as 10°C (50°F) and remain unaffected in their functional properties at temperature levels up to 43°C (110°F). It should be noted that even under the best storage conditions, there will be fat deterioration; therefore, a regular schedule of sample collection is recommended to determine the peroxide value and the level of free fatty acids.
Liquid egg handling
Most bakeries that require eggs in their production use them in their frozen state, either in 30-lb metal cans or buckets, or as frozen blocks packaged in some type of corrugated container. However, if the requirements for eggs are sufficiently large, definite economic advantages can accrue from the use of liquid eggs in bulk. Eggs are among the most biologically unstable food products so their handling in an unfrozen state is circumscribed by rather stringent sanitary controls.
The principal requirement, aside from exemplary housekeeping, is unfailing temperature control. Liquid eggs are most stable at temperatures of 1.6 to 3.3°C (35 to 38°F). When their temperature rises above 4.4°C (40°F), bacterial growth accelerates rapidly, and their holding period becomes correspondingly shorter. According to Grant (1972), the temperature of liquid egg products at the outset of shipping should be about 1.6°C (35°F) for yolks and 4.4°C (40°F) for egg whites. Because many tank trucks lack refrigeration capacity beyond that required for temperature maintenance, deliveries must be completed within 24 to 33 hours if temperature increases greater than 1 to 2 C° (2 to 3 F°) are to be avoided. The dairy-type tank trucks used for liquid egg transport have maximum capacities of up to 40,000 lb. For smaller shipments, self-refrigerated portable tanks can be used. These tanks hold about 1,800 lb and are handled by fork lifts.
To justify economically a liquid egg handling system, a bakery’s minimum use of eggs should be no less than 40,000 lb every 20 days. This level of use will require two 5,000-gal tanks, one for holding and the other for receiving, and refrigeration capacity sufficient to maintain both tanks at temperatures no higher than 4.4°C (40°F). The same considerations regarding tank design and tank fabricating materials that govern liquid shortening tanks also pertain to liquid egg storage tanks.
Based on the above discussion, it is quite difficult to store liquid eggs because of the high potential for micro-organism growth. Such concern especially affects the cookie manufacturing environment where all equipment needs to be sterilized because eggs are classified as an allergen.
Eggs contribute to the tenderness and fine texture of cookies by stabilizing the gluten matrix and the emulsifying the dough mix. They also contribute to the structure, moisture retention, flavor and a brown color to the baked product (BCMA 2002b). Eggs are normally added to the creamed sugar and shortening in the beginning mixing stage to insure complete incorporation and avoid lumping and brown spotting.
In recent years, egg substitutes have gained popularity when eggs are required in a formulation but plants do not want to deal with storage and handling of real eggs. They are either purchased in frozen or spray dried form. Using eggs in the cookie manufacturing process is typically expensive, and their emulsifying effect on fats can be obtained from other more stable sources. Pasteurization of egg products is required to destroy pathogenic organisms, particularly Salmonella, which poses a serious health hazard.
Biscuit and Cracker Manufacturers’ Association (BCMA). 2002b. Cookie and Cracker Manufacturing, Vol. II. The association: Silver Spring, MD.
Grant, F.R. 1972. Recent developments in eggs. Proc. Am. Soc. Bakery Engrs. 48: 150.