Applications

Fats and oils play a variety of roles in baking. They make the crumb-or interior of a baked good-soft and easy to chew. They provide lubricity both in the manufacturing process (for example, the release of product from baking containers) and in the moist feeling in the mouth when consumed. Fats and oils are critical to the structure of baked goods, contributing to such factors as the pliability, rise, flakiness, strength and airiness of the product during manufacturing and freshness after manufacturing.

These different characteristics allow the baker to manipulate his ingredients to produce foods with unique textures, appearances and performances. The table shows the fat contents of various baked goods and the chart shows the basic structures of fats used in baking.

The way a baking fat or shortening is formulated affects its plasticity, a property that describes how soft or pliable it is at given temperatures. These baking fats must strongly resist the hydrolytic effects of water as it "bakes out" of doughs, yet simultaneously must strongly cling to or wet the expanding dough's wall structures to provide gas-tight bags, stretchable films, and energy.

The wetting action comes from surfactant mono- and diglycerides. The gas-tight structures and stretchable films are a result of the combination of the fat with protein and starch. Fats remove energy from the dough (through crystallization) as they cool, and lose energy derived during the dough kneading process. The greater the percentage of saturated fatty acids in the base fat or oil being used, the higher the melting point and the more energy that has to be transferred to the fat to disrupt (melt) the solid crystals. These saturated fatty acids may be naturally occurring, or they may have been produced by hydrogenation during the oil refining process.

Today most bakers use hydrogenated vegetable shortenings in their formulas. These products have replaced tallows and lards that were used almost exclusively until the early 1900s when hydrogenated oils were introduced. These hydrogenated, semi-solid (plastic) fats and shortenings may be produced from a single oil, or they can be blends of oils. With both saturated and unsaturated fattyacids present in such processed fats, melting occurs more gradually. This allows food surfaces to be coated and provides a continuous coating effect in your mouth (mouthfeel) when eating traditional baked goods.

Bakers select fats of different melting characteristics for different baked foods and end uses. Harder or higher melting fats are used in cakes, doughnuts, and cookies, so that they do not become soggy if the fat formula (emulsion with water) breaks down. Icings and coatings such as glazes use fats which melt at even higher temperatures to achieve hard, crisp glazes or coatings.

There is a reason that hydrogenated vegetable products and lards used for baking are called shortenings. They reduce the amount of binding between gluten proteins and carbohydrates, softening and tenderizing the baked foods' texture. This results in a shortening of the time it takes to chew and swallow the baked goods. These semi-solid, plastic or partially hardened fats also trap air during the whipping process, helping to establish the grain or cell structure of the product.

The addition of fat to the product to be baked gives the product a greater volume, which enhances keeping qualities. The ratio between liquid and solid components in a fat have a direct affect on this parameter. During proofing and kneading, the liquid portion is retained within a matrix by the solid fat component, thus strengthening the dough during proofing and handling. During baking, the fat works as a lubricant on the gluten structure. This makes it more extensible and, also, reduces CO2 diffusion out of the dough. This enhances the formation and size of loaves. In fact, doughs with added fats tend to expand for a longer period than those with only the fats (lipids) derived from the cereal itself.

In the distant past, someone discovered that adding eggs to flour improved the quality of their baked foods. At that time, no one knew that lecithin in egg yolks acted as the emulsifier to hold their dough together. The most common type formed in baking, however, is the oil-in-water emulsion, in which the fat is surrounded by water molecules. To form an emulsion, surfactant materials (wetting agents) are necessary. The most common emulsifiers used in the baking industry today are mono- and diglycerides, lecithin, and the lactylated mono-diglycerides. Manipulating the ratio of fat solids and emulsifiers affects the extensibility of the dough used for breads and cakes even at protein-setting temperatures.

Chemically leavened cakes and cookies contain fats in emulsified form to help retain aeration and gasification in the batter. The form of the fat makes a difference here. The balance of liquid to solid fat can limit cookie batter spread, with solid forms controlling spread better than liquid types. Cake volume typically decreases when using liquid fats unless a significant amount of emulsifier is added to maintain foam stability. High fat (high solids) yields a tender crumb, while high oil (high liquid) yields moister, fresher perceptions.

Puff pastry requires shortening made with high solids, high melting-point fats to produce flaky layers. These pastries leaven mostly by steam, and the fat must be retained unmelted during proofing and long enough into baking to maintain the layering of the pastry, separated by fat. Emulsifiers make the layers of dough more extensible.

During the baking process, one of the processes which occurs is that moisture is driven off from the food being baked. Cakes, breads, and muffins generally have approximately 30 percent moisture after baking. This water is integrally bound to the starch and protein in the dough, so that it will not be available to the senses of the person eating the product. When a bite of a piece of pound cake is taken, the fats that were used in the dough melt and coat the tongue. The resulting cooling and coating sensation is perceived as "moistness".

Fats play a major role in ensuring that baked foods release cleanly and can be easily removed from their cooking trays or pans. The fats may be part of the food, or they can be applied to the tray "greasing the pan," so to speak.

Deep-Fat Frying Fats and oils are used in both industrial and foodservice applications to fry a wide range of products including doughnuts and other pastries, snacks, coated products, prepared foods and nuts. The oil acts as a heat-transfer medium, moving energy in the form of heat into the food and pumping a portion of the water out. Frying is, in essence, a dehydration or drying process. The rate of this heat transfer is a function of the surfactants in the oil. High levels of surfactants (soaps, polymers, etc.) may result in excessive contact between the oil and food, yielding a product which may be improperly cooked, dark in color, and excessively oily. Different types of fats are used for frying different foods. Tallows or tropical oils were traditionally used to produce doughnuts and other pastries because of their highly desirable flavors and optimum surfactant contents. Most pastry fryers have switched to hydrogenated vegetable shortenings. These fats are fairly hard. Frying doughnuts in liquid oils may cause "cracking" of coatings or glazes because they do not solidify in the same manner as more saturated fats.

Snacks, such as chips or nuts, are most often fried in liquid oils which have been lightly hydrogenated for stability. Frying a chip in a hard fat would give it a glassy appearance and undesirable taste. Many chip manufacturers favor cottonseed oil because of its performance and unique flavor characteristics. Nut producers often fry in oils from the nuts they are frying. And several snack producers now use oils very low in saturated fats, which are inherently less stable, so they can declare the product to be "low in saturated fat." Manufacturers of coated products tend to fry in harder, hydrogenated fats, as coated products are very abusive to the oil.

The selection of the frying oil or fat for each and every operation depends on a variety of factors, including cost, desired food quality and marketing niche. The most important issue is the food, however. If it doesn't taste good and meet the buyer's expectations, the manufacturer or operator won't be in business very long.

There is a direct relationship between food and oil quality. As an oil degrades, the quality of the food produced in that oil changes. This relationship may be seen in the Frying Oil Quality Curve developed by Libra Laboratories.

As an oil degrades from "Break-In" to "Runaway," the ability of that oil to produce high-quality food changes. The changes in food quality are reflected in the changing chemistry of the frying medium, especially changes in surfactant load. The goal for the food processor is to maintain his oil at the top of the curve for as long as possible, so that the best quality food is the result.

In 1967, Robertson proposed the following principles for oil maintenance.

Proper design, construction, and maintenance of equipment. As with any process, frying is most efficient when using the proper system. Most fryers are built to order, although it is possible to purchase used equipment. To ensure the best use of a system, it should be product specific and maintained according to the manufacturer's instruction. Purchasing equipment which may be used for multiple products or styles of products may be less expensive initially, but it's really not possible to operate such systems at peak efficiencies. When purchasing a system, look closely at the manufacturer's technical support program.

Proper operation of equipment. Good suppliers provide detailed operating instructions and will take the time to train operators. As part of operations, process development must also be considered. If a process calls for a fryer to operate at 380°F + 5°F, that is the temperature at which it should be run. Raising oil temperatures to counteract a perceived problem with product quality only damages the oil and accentuates the problem.

Properly clean equipment. Drain the oil, rinse the fryer to remove gross contaminants, boil out the unit with a caustic cleaner, drain and neutralize the caustic cleaner, rinse the fryer with an acidic solution to neutralize residual caustic, and rinse to remove residual salts and soaps. Be sure that the unit drains properly so no water remains in the system. If necessary, workers must scrub residual polymer from side walls, heater tubes, and other areas where it accumulates without scratching surfaces.

Minimize exposure to ultraviolet (UV) light. Ultraviolet light will catalyze the degradation of triglycerides. UV light attacks double bonds in the unsaturated fatty acids producing by-products, which can act as pro-oxidant materials. These can lead to undesirable off-flavors and can compromise shelf-life.

Keep salt and other metal sources from the oil. Metals are strong catalysts and pro-oxidants. A tiny bit of copper can "turn" the contents of a fryer. Oxidative ability varies between metals. Sodium and calcium are weak compared to copper and other transition and heavy metals (i.e. -Cu > Brass > Fe > Zn > Stainless Steel > Mg > Ca > Na).

Filter regularly. Particulates from fried foods can darken oil, contribute bitter flavors to food, impede heat transfer, and ruin the appearance of foods.

There are two basic kinds of filtration being used in the industry today; passive and active. Passive systems simply remove particulates by a sieving action; active systems contain materials which react with soluble components in the oil, removing them. There are a number of active systems on the market today, which are gaining increased acceptance in both industrial and foodservice applications as they save operators money when properly used.

Monitor food quality. The food is what people eat, not the oil, so all programs that control quality must emphasize the food.

When subjected to stress in the food production process, fats and oils are changed. These stresses can produce undesirable reactions and reaction products, which can compromise the performance of the fat or oil as an ingredient or in deep-fat frying, or produce off-odors and flavors which can render a food or the oil unusable. Many things which can initiate degradation reactions, including heat, light (especially UV), metals, salts, water, and other foods. One of the roles of packaging is to protect fats, oils and foods from these reactions.

Oxidation: The primary degradation reaction for fats and oils is oxidation, also known as rancidity. Oxidation of fats and oils can yield off-flavors which will cause the food to be rejected by the consumer. These off-flavors and odors are the result of the formation of hydrocarbons, ketones, aldehydes, epoxides and alcohols. Oxidation reactions may be initiated in the presence of metals, light, heat and especially peroxides. Not all metals have the same effect.

Copper is the greatest initiator. In fact a single copper penny in a fryer can destroy all the oil in short order. In foods containing fats, the rate at which these off-flavor-producing reactions occur is one of the primary factors in determining shelf-life. In baked goods, the other factor which compromises shelf-life is staling. These two degradation reactions are often lumped together, but they are different. Rancidity and off-flavors result from oxidation of the fats, whereas staling is related to moisture migration and loss of water from the food. Staling and rancidity reactions may, however, be synergistic.

Unsaturated fatty acids must be protected from oxygen. This may be accomplished using antioxidants and/or by packaging. Some of the antioxidants commonly used are BHA and BHT, tocopherols, and TBHQ, frequently with citric acid or a derivative added as a metal chelating agent. No single antioxidant works in all systems. If a processor decides that antioxidants will give him added shelf-life or more security, it is essential that studies be conducted to ensure that the additive will not compromise the product.

Hydrolysis: When water is introduced to an oil, the ester bonds between the glycerol backbone of the triglyceride and the fatty acids are hydrolyzed producing diglycerides, monoglycerides and free fatty acids. The mono and diglycerides are emulsifiers, which further promote hydrolysis reactions. As part of the reaction, water molecules also are split and the resulting hydrogen and hydroxyl groups are added where the bond was broken. Hydrolysis is very common in deep-fat frying where the water released from the cooking food acts to initiate the reaction. Traces of caustic cleaners may also encourage hydrolysis.

Polymerization: Heating oils results in a series of reactions in the bulk oil (see Fritsch diagram). The breakdown products in the oil react with one another to form a wide range of compounds including both oxidative and thermal polymers. It is believed that polymers are formed by direct linkage of carbon to carbon atoms or through oxygen bridges. These are very stable entities, not subject to distillation (escape in the form of steam). They accumulate in the oil and eventually begin to plate-out on fryer walls, forming the brown shellac-like material visible on dirty fryers. Polymers make up the largest single group of compounds in degrading oils, and are considered by many to be the best indicator of oil degradation. Polymers also contribute to foaming, increased viscosity and darkening of the oil.

Pyrolysis: One of the compounds that forms when oils are overheated or pyrolized is acrolein, a pungent irritant, which can make the working environment quite uncom-fortable. Acrolein is formed from the glycerine left from the hydrolysis of triglycerides.