Technical Talk: July 2007

Mission Possible: High-Quality Frozen Dough

This column is written by Dr. John Michaelides of the Guelph Food Technology Centre, 519-821-1246, www.gftc.ca

Question: How are baked goods affected by freezing; and, what needs to be taken into account in order to produce high-quality frozen bakery products? 

Answer: Freezing is an excellent means by which the staling of baked goods (and especially breads) can be completely inhibited, or greatly reduced. The effect of the freezing on the freshness of bread has been thoroughly investigated – since as early as the 1930s. Baked goods that have been frozen prior to becoming stale will remain fresh for several days after thawing.

Freezing of baked goods is not carried out just to prevent staling; it has become a necessity in order to satisfy consumers’ demand for quality and freshness. Today, production of baked goods is carried out on a massive scale in centralized locations, and the resulting products must be transported great distances to reach consumers. Therefore, it is necessary to ensure that these baked goods have a much longer shelf life than is possible for fresh products, and freezing has been proven to be a practical approach. In addition, due to the lack of skilled bakers at the store level, this evolution has been necessary to ensure consumers have ready access to good-quality, fresh-baked goods.

Freezing of 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 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 good quality, finished products that will satisfy consumer demand.

Freezing the dough prior to proofing and baking was largely expanded due to the introduction of in-store bakeries, where the dough was thawed, proofed and baked by semi-skilled bakers. In addition, frozen dough appeals to a market segment of consumers who prefer to do their baking at home, and do not have the time to prepare the dough. Finally, various institutions, catering to large groups of people, rely on frozen dough to deliver uniform, good-quality, economical baked goods.

The production of frozen dough involves the mixing and development of the dough, which is divided into appropriate pieces, then 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.

In order to ensure full activity of the yeast, the amount should be increased. Some references suggest that the level be increased to four to six per cent.  In addition, it is suggested that if the formula contains shortening, this also needs to be increased to five per cent. Other researchers indicate that a slight decrease of the water absorption is required. In order to develop the desired crust colour in frozen bread, it is necessary to maintain a sugar level of six per cent, and the non-fat dry milk to four per cent.

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 that a good oxidation system be utilized, and the normal reducing agents be utilized at their lowest level or be eliminated entirely. A good oxidation system is essential when mixing at lower temperatures (as is the case with dough destined for frozen storage). Mixing at lower temperatures will have a detrimental effect on final volume, and grain structure of the bread. The lower the temperature of mixing, the higher the amounts of oxidants required for good performance.

Frozen dough stability is the ability of the thawed dough to proof in an acceptable period of time, and to bake into a loaf of normal volume and bread characteristics. There are several factors that affect the frozen dough stability. Such factors include 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.

It has been suggested that the fermentation activity has a detrimental effect on yeast viability during frozen storage for two reasons. When yeast is present in its dormant state, it has a better survival rate when it’s frozen. In addition, the various highly volatile fermentation products remain within the frozen dough, and can depress its activity during the fermentation period after freezing and thawing. Opinion is divided about the effect of different kinds of yeast.  Some suggest that fresh compressed yeast performs better in frozen doughs than active dry yeast. However, others indicate that higher amounts of active dry yeast perform better than fresh compressed yeast. This may be affected by other factors in the dough system. Flour — and especially the 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 role in the stability of frozen dough. Rapid freezing has a detrimental effect on the survival of the yeast cells, because it forms ice crystals within the yeast cell. These crystals, in turn, damage the yeast cells’ internal structure, essentially killing them.

So far, I have been discussing the issues associated with frozen dough stability. Partially baked goods are products that are baked to the point where they are fully formed to their final volume and shape, but lack the characteristic brown colour and the final flavour development. As with earlier examples of freezing, 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 (from 120 to 150 C), and the baking time increased to the extent of achieving the volume without the crust colour. In addition, the dough absorption needs to be reduced, and the dough mixed at a higher temperature. The yeast’s level and yeast food should be reduced slightly to eliminate excessive “oven spring,” and the fermentation should be carried out at warmer temperatures (38 to 40 C) to promote fast proofing. 

Similarly, fully baked goods can be frozen for a long period of time, and when thawed, will produce good quality fresh products, adding to consumers’ convenience. Moisture and flavour loss, as well as absorption of odours from other products during frozen storage, is a problem that needs to be addressed in the production of these products.
 
For more information, or fee-for-service help with product or process development needs please contact the GFTC at 519-821-1246, by fax at 519-836-1281, or by e-mail at gftc@gftc.ca.