Chilling Developments for Doughs

July 2001

There’s nothing like the smell of freshly baked bread to draw consumers into a grocer’s bakery section. This has led to the popularity of programs such as the “We Bake While You Shop,” kiosk-fresh concept for supermarkets, convenience stores and restaurants by The Stonemill Bakehouse Limited, Scarborough, Ontario. Consumers can stop by the bakery section of their local grocery store, order fresh-baked artisan bread, and add it to their grocery cart in 20 to 25 minutes. This freezer-to-oven technology allows even non-bakers to produce high-quality, fresh baked goods, while reducing inventory and waste problems.

The wholesale bakery industry has evolved slowly to more centralized, high-volume production. The skilled-labor shortage makes this the most efficient way to produce high-end baked goods. Using frozen dough also saves time, space and equipment costs, making it especially attractive to small retail or in-store bakers. While many in-store bakeries offer products baked on the premises, about 90% of the product preparation is done at a central plant. Many products require only thawing.

The frozen baked-goods category includes a wide variety of products. For example, the Rich’s Products Corp., Buffalo, NY, product line includes a sweet-goods category with cookies, cakes, cinnamon rolls, doughnuts, pastries, biscuits, bagels and pretzels; parbaked rolls and European classic breads; and pizza crust in dough balls, sheeted dough and parbaked varieties. Bill Gisel, CEO of Rich’s, says that the company’s primary target is foodservice and bakery/deli chains. Rich’s recently acquired a line of frozen, finished cakes to round out its frozen product line, and notes that frozen pizza dough is a primary growth area.

Other major players in the frozen and refrigerated category include Pillsbury, Nestle, Sara Lee and Earthgrains. These and many other companies offer a wide range of products. Frozen retail waffles and bagels represent a significant market sector. Refrigerated baked goods include tortillas, biscuits and ready-to-bake cookie mix. Refrigerated ready-to-bake pizzas, complete with toppings and cheese, are a growth category in the deli section. Rounding out the group are frozen piecrusts, cheesecakes and toaster pastries.

The three general types of frozen baked goods include: “bake-off” products that must be thawed, proofed and baked; fully baked “thaw and sell” products; and “parbaked” products that are partially baked and then frozen, thawed and given a final bake at the store or home level.

A successful frozen or refrigerated dough or batter is expected to produce an end product similar to a freshly made one. Refrigerated products generally have a shelf life of several days. Frozen doughs can be held up to three months or longer. Let’s first look at the issues facing the frozen dough manufacturer.

Quick and cool
In frozen doughs, the goal is to produce a loaf with good dough strength, extensibility and fully developed gluten to yield a finished product with good volume and crumb structure. “The two major challenges for frozen dough manufacturers are to maintain yeast activity and keep a cool process,” notes Jan van Eijk, research director for American Yeast/Lallemand, Montreal. In frozen-dough production, process parameters are just as important as ingredient selection. Bakers need to reduce fermentation before freezing while optimizing dough development during mixing.

A no-time dough process has a short time between mixing and freezing. This could be as short as a couple of minutes for the first dough, and much longer for the last pieces to go through the forming stages. Small batches minimize the time it takes for the last dough piece to reach the freezer.

To achieve a low dough temperature, bakers cool ingredients and water. The ideal dough temperature after mixing is 20ºC (68ºF). Bakers may need to add ice to their water to achieve the proper dough temperature. They might also delay addition of salt and yeast until later mix stages. These procedures improve dough development and minimize yeast activation before freezing. Care should be taken to fully develop the dough without raising dough temperature too much, thus enhancing yeast fermentation prior to freezing. Frozen dough can become stiff and difficult to machine, requiring some formula adjustments.

According to van Eijk, bakers achieve better results with smaller dough batches, which allow for a more even proof. Frozen-dough manufacturers that employ blast freezing should avoid freezing too long, which can cause excess damage to the yeast. Once frozen, the optimal storage temperature for frozen dough is approximately -4ºF. It is essential to maintain a constant temperature during transportation and storage to preserve dough quality, as repeated freeze/thaw cycles produce free water that recrystallizes and ultimately reduces bread quality.

Dough is a good insulator — large pieces need to be thawed in the refrigerator at approximately 35º to 40ºF to avoid temperature gradients that cause uneven dough proofing. Smaller dough pieces, such as rolls, can thaw at room temperature, thus eliminating excessive handling. Other helpful tips are to use a first-in, first-out scheme and to never refreeze pieces once thawed. Extending proof times may help compensate for any losses in yeast activity during storage.

Yeast’s big chill
Yeast activity can deteriorate significantly as frozen-storage time increases. Frozen doughs must not only make it into the freezer with good fermentation viability, they also must withstand freeze/thaw cycles in the freezer, shipping and storage at a second location. Retail products also must endure a trip home from the grocery store, survive additional time in the home freezer, and still rise to the occasion when the end user pops them in the oven.

Cryoresistance is the yeast’s ability to withstand frozen storage. “Positive results with frozen dough are greatly enhanced by the presence of trehalose, a cryoprotective compound found in yeast,” says van Eijk. Trehalose is a naturally occurring non-reducing sugar containing two glucose molecules bound in an alpha, alpha-1, 1 linkage that helps protect protein, and stabilize organisms during freezing and desiccation. In addition to occurring naturally in yeast and many other common food sources, trehalose is self-affirmed as a generally recognized as safe (GRAS) food ingredient.

Yeast with good cryoresistant properties tends to stay dormant longer and activates more slowly when it’s mixed into dough. Yeast cryoresistance varies between different yeast strains; yeast strains with better cryoresistance usually have lower activity. Yeast manufacturers will try to control both the activity and cryoresistance of yeast batches used in frozen dough applications. To test their yeast, bakers can use the Eagle® quick test for yeast cryoresistance; it takes approximately four hours and correlates well with conventional storage.

The longer the dough will be held in frozen storage, the more important it is to choose yeast with good cryoresistance. Most frozen dough products can be produced by a short, no-time dough process and have a fast turnover, typically less than two weeks of frozen storage. For such products, yeast cryoresistance is less critical and regular yeast works well. For a three-to-six month storage, a special yeast strain might be more important. Also, more critical applications, such as frozen croissants and laminated pastries, might require special cryoresistant yeast.

Typically, frozen doughs require twice the amount of yeast as regular doughs. Frozen-dough manufacturers always should choose the freshest yeast available. Most bakers pick fresh yeast in cream or compressed form for frozen dough; instant yeast rarely is used because it is sensitive to cold shock. A frozen, dry yeast product with 80% solids and 20% moisture also has been developed specially for frozen-dough applications.

Basic ingredients
Bakers achieve the best results by using strong, high-quality flour. To increase dough strength, they can adjust the flour blend by using flours with a higher percentage of protein, or add vital wheat gluten. A hard, red, spring wheat with a protein level of 12% to 13% and a moisture level of 14% generally yields good results. Flour should be low in damaged starch and enzyme activities. High-protein flours are not recommended because they may require excessively long mix times. Water absorption generally is reduced by about 2% to 4% to facilitate handling of dough after thawing.

Rich, sweet doughs with higher levels of shortening and sugars freeze better than lean doughs. Suggested formulation levels for sweet doughs are 5% shortening, 6% sugar and 4% nonfat dry milk. Rich doughs typically require more yeast than lean doughs. The proper selection of emulsifiers, enzymes and dough conditioners also is important for frozen dough.

The most common emulsifier used in frozen doughs is diacetyl tartaric acid ester of monoglyceride (DATEM). “Look at the ingredient legend for almost any frozen bread product and you will find DATEM listed,” notes Dana Boll, bakery technical manager, Danisco-Cultor, New Century, KS. This dough strengthener interacts with gluten to form a homogeneous network important to the bread-making process. The improved gluten network increases gas retention in dough resulting in a good bread volume. Typical usage levels for frozen dough are 0.1% to 0.3% DATEM based on flour weight. The emulsifier alters the water-binding properties of dough. While the actual mechanism is unclear, one theory is that emulsifiers provide dough strengthening by helping form lamellar aqueous films between the gluten and the starch. They also interact with the fat in the flour and dough, which also may improve the lamellar structure and increase its flexibility. But whatever the mechanism, the stronger dough results in a drier surface, better dough stability and improved machinablity. This facilitates rounding and molding of the dough, as the dough will not stick to the equipment. Other emulsifiers that are used often in frozen doughs include sodium stearoyl lactylate and ethoxylated mono- and diglycerides.

Bakery enzymes also can improve frozen-dough performance. Enzymes with amylase and xylananse activity modify the starch and arabinoxylan in flour for an optimal baking performance. Baking enzymes improve dough-handling properties and gluten structure, making it more homogeneous and flexible, which improves the ability to retain the gas produced by the yeast during fermentation. Typical usage levels for bakery enzymes are 100 to 200 ppm.

Oven spring
All that time chilling in the freezer really takes a toll on yeast activity — yet that piece of previously frozen dough is expected to spring to life in the oven, and produce finished bread with good volume and close, even crumb. Baked goods with a long fermentation time generally do not require high levels of oxidants because the fermentation process adds strength. However, with no-time frozen doughs, proper oxidation is critical to achieve proper oven spring and an acceptable final loaf volume.

A number of oxidizers are used in the baking industry, each with a different reaction time. Potassium bromate was an ideal oxidizer for regular doughs in terms of its release profile, notes Michael Beavan, manager of bakery ingredient development and quality control, Watson Foods Co., West Haven, CT. Bromate’s slow release meant that a significant portion still was available at the critical proofing and baking stages, providing good oven spring and resulting in improved loaf volume. However, the shorter ferment times for frozen doughs required a faster-acting oxidizer. A combination of bromate and ascorbic acid, an intermediate acting oxidizer, works well. However, concerns over the negative health implications of potassium bromate have prompted most bakers to replace bromate with alternative leavening systems.

Fast-acting oxidizers include azodicarbonamide (ADA), potassium iodate, (KI03) and calcium peroxide. Many of these alternative oxidizers release too early in the mixing stage, leaving little strength for those important proofing and baking stages. This is especially significant in frozen doughs. Encapsulated forms, such as ascorbic acid and ADA, allow a baker to push the functionality to the end of proof, giving good activity in the final proof and an impressive oven spring. Coating the ascorbic acid also slows down its release during mixing to prevent over-aging of the dough. Recommended usage levels in frozen doughs are at least 60 ppm and frequently 90 to 120 ppm of ascorbic acid.

Many companies offer lines of dough-conditioner blends specially formulated for frozen doughs. These products are frequently high in ascorbic acid and also may include emulsifiers, such as DATEM, and enzymes.

One factor previously believed to contribute to poor loaf volume in frozen doughs is the reduction of gluten disulfide groups by reducing substances released from dead yeast cells. More recently, research concludes that it is actually the reduction in cross-linking action in the gluten networks that reduces loaf volume in frozen doughs. Generally, it is advised to limit reducing agents in frozen doughs.

Artisan touches
The extra cost of freezing dough, and the higher costs of shipping and storage, means that frozen-dough systems generally are more expensive and not used extensively for commodity items, such as white pan bread. However, high-end whole-grain and artisan breads are excellent candidates for frozen doughs.

Watson Foods also has a line of special grains and sours specially processed for use in frozen doughs. An example of this is a mixture of wheat sourdough, soybean grits, oats, sunflower seeds, flaxseed and rye flour. Preswelling the grains allows them to hydrate immediately and retain moisture well, making them ideal in frozen doughs and/or parbaked products to minimize water loss during baking and freezing. Other products contain fermented sour that compensates for the lack of yeast flavor development that frequently occurs in frozen doughs.

Traditional long fermentation processes develop a pleasant, strong yeast flavor and aroma. Because most frozen doughs are no-time doughs, they lack those appealing flavor characteristics. “One solution is to add a yeast flavor,” notes Mitchell Duffy, bakery and cereals project leader, David Michael & Co., Philadelphia. Both flavor and aroma add to the consumer appeal, especially in a situation where the smell of freshly baked bread is expected to attract customers.

Plus, for many sweet breads, cinnamon and other spices are added for flavor. Cinnamon may bake off, leaving little flavor in the finished product. Cinnamic aldehyde can be detrimental to yeast activity. Encapsulated cinnamon ensures that yeast activity is protected and a pleasant cinnamon flavor remains in the finished baked good.

Getting a chemical lift
While frozen breads, rolls and sweet goods make up a large portion of the frozen-dough market, frozen pizza is another significant market sector. In recent years, self-rising pizzas have gained tremendous consumer appeal. Besides the normal rigors of frozen dough, these products also must withstand the abuses of distribution, which includes the grocer’s freezer case, the ride home in the consumer’s car, and a period of time in the home freezer, notes Micky Gross, national sales manager, Balchem Corporation, Slate Hill, NY. After shopping at the grocery store, a typical consumer might stop to pick up the dry cleaning, fill up the gas tank, and drop one child off at soccer practice, before arriving home with the frozen pizza. This product then sits in the consumer’s home freezer for over a month. In these products, the yeast activity may have deteriorated significantly, therefore chemical leavings are needed to give that pizza crust rising power.

A typical chemical-leavening system includes sodium bicarbonate and various leavening acids. These produce CO² gas through the reaction of the acid and bicarbonate base. The point at which gas formation occurs is controlled mainly by the compounds used. To minimize gas release during mix and bench phases, and maximize it during baking, product designers typically will use sodium acid pyrophosphate in refrigerated dough products, such as biscuits, to allow the dough to be held for long periods, even at elevated temperatures.

In frozen systems, freeze/thaw cycles create free water that reacts with traditional chemical leaveners, reducing their activity over time. Using encapsulated systems solves this problem. Generally, the soda portion of the leavening system is encapsulated, notes Vernetta Dally, Balchem’s manager of applications. The encapsulating material, typically a vegetable fat, melts at the bake temperature, allowing the leavening acids and bases to react and form CO². Different types of encapsulated leavening systems have been developed for different products to accommodate different formulation and processing parameters.

Encapsulated leavening also finds use in a variety of other chemically leavened baked goods. A good example is institutional or fast-food muffins. It’s very labor intensive to have an individual come in to each location daily and mix a fresh batch of muffin mix, which would typically need to keep for 24 hours in a refrigerated state. Dally explains that with encapsulated leavenings, fast-food companies can prepare and freeze muffin mix, then thaw at each retail outlet and use over a five-day period. Muffin batters that are higher in sugar and shortening generally freeze better. Preportioning the batter at the central plant provides additional labor efficiency and a more consistent product.

This technology also works well for other chemically leavened products, such as pancakes and biscuits. A fresh breakfast sandwich typically is made from a frozen biscuit that, a few hours earlier, resembled a frozen hockey puck. These products perform much more consistently with encapsulated baking soda.

Balloons and sponges
Various gums and stabilizers add another tool to the frozen-food formulator’s bag of tricks. Allen Freed, president, Gum Technology, Tucson, AZ, has a novel way of explaining how specialty gum blends work in frozen baked goods. A variety of gum blends can provide special rheological properties that alter the final product’s texture.

Freed explains that some gums act like balloons holding water. These gums hold their water well, but once they burst, they lose their water-holding capacity. Other gums work like sponges — they lose water gradually to evaporation, but do have the ability to absorb additional water. If the “balloons” burst, they can give up their water to the “sponges.” By using combinations of “balloons” and “sponges,” Gum Technology has developed synergistic gum blends suitable for various applications, including refrigerated and frozen baked goods.

For example, one product, a combination of guar gum, xanthan gum, food starch, and mono- and diglycerides, eliminates freezer burn and bursting in frozen tortillas. This can be used at a level of about 1.8% of total weight to eliminate hard crusting on the edge and helps prevent cracking and blistering.

Other gum applications include bagels and sweet goods. Gums can increase shelf life in fresh baked goods up to 50% and provide stability to frozen baked goods through seven or eight freeze/thaw cycles. In refrigerated tortilla applications, gums can permit the addition of 10% to 15% rework in batches where the scraps would normally be thrown out. This results in a significant savings to manufacturers.

Parbaked possibilities
Another labor-saving frozen option is using a parbaked product. In this technique, the baked good — typically yeast-raised goods, such as bread and rolls — is almost completely baked out, and then frozen. The end-user takes the frozen product and finishes the bake at a relatively low temperature, using convection heat to shorten the time in the oven.

This method provides several advantages. The rigors of freezing do not have a great impact on the dough formulation. The critical steps to the overall texture and quality — proofing and baking — are essentially the same as in a traditional process. Therefore, formulators can choose conventional yeast strains — and don’t need to consider deterioration of the gluten structure during freeze/thaw cycling — so specialized dough strengtheners or improvers are not a necessity.

Parbaked products can minimize labor requirements for in-store bakeries and still mimic the quality and tantalizing fresh-baked smell of from-scratch or frozen doughs. Not only are tedious mixing and proofing steps eliminated, but also the skill level for finishing off a parbaked loaf is minimal. Developing the optimal freezing process keeps breads from staling, and is especially useful in artisan products that require a crispy crust, because freezing can also minimize moisture migration from the crumb to the crust. Since the higher storage costs for the bulkier frozen products is a consideration, using this process for pricier artisan breads vs. commodity items also makes sense.

While frozen storage minimizes staling, the freezing process does increase the staling rate due to starch retrogradation when the temperature is between approximately -8º and 4ºC. Experts suggest that freezing rate and storage temperature be optimized to minimize unfrozen water, and to maintain the product at temperatures below the product’s glass transition temperature (the point where molecular movement stops in the unfrozen liquid portion). Formula modifications can aid in changing this temperature to those commonly encountered in frozen storage.

Preservation calls
Baked goods in the refrigerator case face some of the same challenges as those in the freezer case, in terms of maintaining gassing power. In addition, the higher refrigerator temperature also raises issues of microbial growth. Studies show that frozen and refrigerated baked good generally are microbiologically safe. When baked or microwaved before consumption, these products are very safe; however, preservatives often are added to extend shelf life.

Bakers generally add sodium propionate to chemically leavened products, and add calcium propionate to yeast-raised baked goods because it does not interfere with yeast activity. Regular sorbic acid cannot be used in yeast-raised products because it interferes with yeast fermentation, but encapsulated sorbic acid can be added to refrigerated bagels and tortillas to boost shelf life.

Nutrients in the deep freeze
Most of the vitamins and minerals used to fortify baked goods generally tolerate freezing well. There are few issues with their shelf life. Freezing actually is beneficial for certain nutrients that can be used to enrich functional bars and similar baked goods, according to Raimund Hoenes, marketing manager, Roche, Parsippany, NJ. The omega-3 long-chain PUFAs (commonly referred to as LCL-PUFA) are made from highly refined and deodorized fish oil. When these products degrade, several of the volatiles produced are associated with strong fishy odors. Deep freezing can help to prolong their shelf life by preventing the oxidation from occurring; this is, of course, when using appropriate packaging.

There is tremendous potential for adding these healthy fatty acids to frozen functional foods, adds Hoenes. They work well in baked goods and can be added to the fat phase or mixed dry in the flour. Consumers today often buy products because of a nutritional claim. Today’s consumers typically reach for a product that bears a benefit message, such as “promotes heart health.” Then they turn over the box and examine the ingredients and the Nutrition Facts.

Topping it off
Many complex products, such as Danish and coffee cakes, are frozen. Bakers have to consider not only the dough, but also the fruit or cheese fillings and icings. All must withstand freeze/thaw cycles, and retain their separate integrity, so they require formulations that maintain freeze/thaw stability.

One of the secrets to formulating fillings and toppings for frozen applications is selecting the appropriate hydrocolloid stabilizer. Typically, formulators will look at modified starches derived from corn. Unmodified, or native, corn starch will easily retrograde or break down when subjected to repeated freeze/thaw cycles. Therefore, starch manufactures will stabilize the starch through substitution, a process where a chemical group is added on the starch’s backbone to prevent the starch molecules from reassociating. Cross linking gives a starch more tolerance to high temperatures, acidic pH and shear, so this modification helps in applications that require multiple cooking steps and low pH, such as fruit fillings. Selecting the proper starch depends on the process, the matrix, storage and handling conditions, and the result desired in the finished product, including characteristics such as clarity, mouthfeel and sheen.

Stabilizer options other than corn starch can work well in certain applications. JennieAnn Reitemeyer, food scientist, Avebe America Inc., Princeton, NJ, explains that potato and tapioca starches have excellent clarity and very bland flavor. When added at levels of 2% to 3% in cream or cheese fillings, they hold water, and minimize bleeding and syneresis. A properly formulated filling will minimize moisture migration and not make the finished Danish soggy.
A variety of gums also can be added to fruit fillings to improve bake stability. To increase freeze/thaw stability, microcrystalline cellulose gel and carboxymethylcellulose (CMC) make good choices, and microcrystalline cellulose gel also aids heat stability and helps prevent boil-out. However, care must be taken to ensure complete hydration of these gums when used.

Avebe also carries a line of potato fibers that bind water, oil and fat. These products act as emulsifiers and can add not only texture, but also enhance the nutritional profile of baked goods.

Another strategy for preserving quality of multicomponent frozen items is to minimize differences in water activity (Aw), and therefore, minimize moisture migration at temperature where the unbound water is still mobile. However, some experiments have shown that less staling occurs in a cake if its Aw falls above that of a filling.

Cake decorating is another labor-intensive activity, and skilled cake decorators are in short supply. The frozen decorated-cake market has expanded greatly in the past five years — cakes are the most popular item in the in-store bakery, and decorated cakes are sales leaders. At central bakeries, cake rounds and layers are baked, decorated and frozen. They then are shipped to grocery stores, where a local decorator can thaw the appropriate size and just add “Happy Birthday Jill,” or “Congratulations Malaika.”

Generally, cake layers for freezing are formulated using some starches and a gum blend to retain moisture. Frequently, bakeries buy wholesale cake mixes for freezing. An extra-moist cake mix works well for frozen applications. A good-quality decorator icing will hold up well in the freezing process. “Tapioca starches can also be used in icing to retain moisture in frozen decorated cakes,” adds Reitemeyer.

Frequently, non-dairy whipped topping is used to replace traditional icing for these cakes. The key for these types of products is to maintain a structure that retains the trapped air. Again, hydrocolloid gums, such as guar and locust bean gums, and alginates can help improve the frozen system by minimizing moisture loss and syneresis, and increasing the structure’s freeze/thaw stability.

Specialty items
Frozen and refrigerated waffles, pancakes and similar breakfast items also are popular. One company, Encapsulation System Inc., Broomall, PA, is working on a refrigerated batter for muffins, pancakes and waffles that could be squeezed onto a hot plate. Individuals with limited mobility, such as elderly people with arthritis, could make “fresh” pancakes and similar items daily, notes Ram Roy, vice-president of the company’s microencapsulated product development. These products contain encapsulated leavening systems to boost shelf life.

Refrigerated cookie dough appeals to the busy mother who likes to share baking with her children, but doesn’t have time to stir up a batch of cookies from scratch, or the single who just wants a handful of fresh-baked cookies. The Pillsbury Company, Minneapolis, has popularized this item with products customized for Christmas, Valentine’s Day and several other holidays. The system for producing these are fairly sophisticated mechanically, but not formulation-wise — leavening is not as critical in these refrigerated cookie doughs as it would be in a biscuit or muffin formulation.

The outlook is rising for continued growth in both frozen and refrigerated baked goods. Bakeries are constantly trying to find ways to take some of the labor out of the bakery and reduce the high cost of finding, training and retaining quality employees. Consumers want fresh-baked quality without the fuss, and are willing to pay a premium for it. As long as central bakeries can produce frozen products that resemble products baked fresh on the premises, expect to see more baked goods spending time on ice.

Sharon Gerdes answers a technical support line for the dairy industry. She also writes and consults for other food industry clients, with emphasis in regulatory compliance and formulating baked goods and nutrition specialty items. Gerdes holds a bachelor’s degree in food science and nutrition from Kansas State University, Manhattan.

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