Technical Talk: June 2014

Freezing is a convenient way to extend shelf life, but formula changes are needed to get a great finished product when thawed

Freezing is a convenient way to extend shelf life, but formula changes are needed to get a great finished product when thawed

Freezing is an excellent way to completely inhibit or greatly reduce the staling of baked goods (especially breads). Although anti-staling agents can be incorporated into formulations to extend shelf life, freezing provides a much longer solution. Today, production of baked goods is carried out on a massive scale in centralized locations; therefore, such products need to be transported to final consumers at great distances. Freezing baked goods can be achieved at the different stages of the baking process. Frozen dough is often available for many uses, but partially baked goods as well as frozen finished baked goods can be produced to serve the consumer markets. Products that are destined for the frozen market, whether in the dough state, partially baked or finished frozen, need changes to their formulation and processes in order to result in a good finished quality that will satisfy consumer demands.

Freezing the dough prior to proofing and baking was largely expanded due to the introduction of in-store bakeries where dough is thawed, proofed and baked as a process that requires semi-skilled bakers.

The process to produce frozen dough involves mixing and developing the dough, which is then divided into appropriate pieces and frozen until used. The dough, as a biological and chemical system, needs to be protected from the adverse conditions of freezing. For this reason certain changes to the formulation are required.

Yeast is the most sensitive dough component when freezing. In order to ensure full activity of the yeast, the amount should be increased. For best results, the baker’s yeast has to possess certain physical characteristics, such as high levels of cryoresistance, high level of trehalose and high speed of adaptation to various substrates. The flour used should have an increased high quality protein level and lower ash content. In addition, it is suggested that the shortening and salt should be increased. Water has an important role in the process of developing ice crystals during freezing and storage of frozen dough. However, through the application of special quality raw materials and defined technological parameters such as freezing velocity and frozen storing temperature, the negative effect of ice crystals may be minimized.

To develop the desired crust colour in the bread, it is necessary to maintain a higher sugar and nonfat dry milk level in the frozen dough formulation. The dough needs to be fully developed at the mixer but the yeast activity should be kept at the minimum level. For this reason, it is essential to use a good oxidation system and lower or eliminate the normal reducing agents. A good oxidation system is essential when mixing is carried out at lower temperatures (as is the case with dough destined for frozen storage), which will have a detrimental effect on final volume and grain structure of the bread. The lower the temperature of mixing, the higher amounts of oxidants are required for good performance.

Frozen dough stability is the ability of dough that has been frozen for a long time to result in an acceptable loaf volume and quality characteristics of the finished baked good upon thawing. There are several factors that affect the frozen dough stability, including formulation, yeast type and quality, the amount of yeast fermentation prior to freezing, the length of frozen storage and the rates of freezing and thawing.

Flour, and especially protein quality, also plays an important role in extending the stability of frozen dough. The addition of various hydrophilic gums such as Gum Arabic can also play a role in increasing the stability of frozen dough. The rate of freezing plays a very important part. Optimum freezing methods reduce the formation of ice crystals, extending the survival of the yeast cells.

In order to provide further convenience to consumers, partially baked or completely baked goods are also available frozen. Partially baked goods are products that are baked to the extent that they are fully formed and are their final volume and shape but lack the characteristic brown colour and final flavour development. These products also require formulation and processing changes in order to result in good-quality finished baked goods. The requirement is to fully develop the volume and shape without the colour and flavour. In order to achieve this, the oven temperature needs to be reduced and the baking time increased to reach the desired volume without the crust colour. In addition, other changes to the process such as dough absorption and mixing temperature are needed. The yeasts levels and yeast food need to be adjusted in order to eliminate excessive oven spring.

Freezing is a convenient way of preventing the staling of baked goods but the freezing process and storage has to be done properly. Various freezing methods are available, including mechanical air blast, cryogenic, and contact plate equipment. The cryogenic method uses liquid carbon dioxide (temperature of -79 C) or liquid nitrogen (temperature of -195 C).  After the initial freezing, the holding temperature of -18 C is satisfactory to yield good results. Bread and other baked goods are normally wrapped or packaged during frozen storage to prevent moisture loss. Moisture and flavour loss, as well as absorption of odours from other products during frozen storage, are common problems. 

Many convenient frozen foods contain a combination of dough (or baked shells) and other food materials. The challenge is to prevent the liquid of the filling formulation from affecting the quality of the dough or baked shell. This can be achieved by carefully formulating both the dough and the filling.

For more information or fee for service help with food technical and processing issues and needs please contact Dr. John Michaelides at John Michaelides Consulting at 519-743-8956 or at Bioenterprise  519-821-2960, by email: j.jmichaelides@gmail.com