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 Chapter 10: Heating and Cooling Equipment — Proofers and Retarders and contributed by Stephen St. Clair-Thompson.
Between the mixer and the oven stand a variety of machines and equipment systems that accommodate the processing stages of intermediate proofing, final proofing and retarding. Each applies time, temperature and humidity to bring out the desired characteristics required for a high-quality finished product.
With regard to the design and use of this equipment, differentiation should be made between proofing and resting functions. Like the relatively short floor time given to doughs held in troughs, intermediate proofing of scaled dough pieces provides rest time that benefits the gluten protein structure of the dough. While taking as long if not longer than bulk fermentation, retarding inhibits, but does not entirely halt, yeast activity and thus supplies both rest for the protein and time for the yeast to develop its flavor compounds and dough conditioning actions. Final proofing functions not only to rest and condition protein but also to foster generation of leavening gases.
The equipment designed and engineered to accomplish these processing stages varies in configuration and size as well as how it employs heat, humidity and time. The chemical and physical processes involved in proofing and retarding are examined in “Baking Science & Technology, 4th. Ed”, Chapter 6, Parts B and F.
Bakers use intermediate proofers or a period of rest time to help yeast-raised doughs recover from the rigors of dividing and rounding, but the final proofer is what enables the leavening to bring bread and rolls to their optimum volume before baking. Intermediate proofers usually operate at the plant’s ambient temperature and humidity, with care taken to avoid drafts that could dry dough surfaces, while final proofers apply controlled heat and moisture to the dough’s environment.
The function of the final proofer is to enable the yeast to contribute leavening gases to the air cells that already exist within the dough’s protein structure, thus enlarging the size of the moulded dough piece by a factor of about 3 or 4. Such yeast activity is best promoted by a temperature of 35 to 40°C (95 to 104°F), so it follows that the environment in which final proofing takes place must be at a temperature of 35 to 49°C (95 to 120°F), with the actual temperature depending on product variety.
Also, the surface of the dough piece must not be allowed to dry out, or the dough piece will lose weight, and its surface will split. Thus, the environment in which proofing takes place needs to have as high humidity as possible.
Dough pieces will be going into the proofer at a temperature of 28 to 30°C (82 to 86°F) on peel boards or in pans. It would be helpful if the dough pieces could be at a higher temperature, but if they were any warmer, they would be too sticky for the moulder.
The yeast requires about 50 to 65 minutes to inflate dough’s air cells and develop the protein structure, so the proofer must be large enough to contain this amount of product.
Finally, dough pieces at this stage are extremely delicate. Any jarring during final proofing can literally knock it back; thus, the mechanical operation of the proofer and the proofer-to-oven transition needs to be smooth.
The fact that the proof time is so long presents a problem to the craft or artisan baker, who wants to have a batch of bread available for the oven first thing in the morning. The solution is the retarder-proofer, a cabinet provided with a controlled temperature and humidity cycle. Normally, it operates as a simple proof box, with a controlled proof cycle; however, for the last batch of the day, it becomes a chiller that retards the fermentation process overnight until the proofer automatically warms up in the early hours of the following morning and starts its proof cycle.
Dough retarding is defined as placing a partially fermented dough under refrigeration at temperatures in the range of 1.7 to 4.4°C (35 to 40°F) and a relative humidity of 85%. Such conditions are not intended to freeze the dough but slow down its fermentation rate so the dough can remain stable for either several hours or several days. While quite useful for preparation of bread and rolls, dough retarding has become an integral step in many sweet dough and puff pastry operations. By subjecting a dough that usually contains high levels of shortening to periodic cooling during its early processing stages, bakers preserve its optimum machining properties through somewhat lengthy and intricate handling operations.
Two refinements are worth mentioning: First, retarding can be set for the period of a weekend or holiday when necessary. Yeasted doughs remain essentially stable for periods up to 48 hours. Second, in the event that the proof cycle is complete but the rack has not been removed, the proofer will cool down, delaying any further development.
Versions are available that will freeze retard; these styles are particularly relevant to larger loaves of 800 g (28 oz) or more.
More on this topic and other related subjects can be found in Baking Science & Technology, by E.J. Pyler and L.A. Gorton.