The term controlled fermentation is commonly used to describe processes in which fermentation is halted through the use of cold, without reaching freezing temperatures. I do not particularly like the term because all fermentations should be controlled. The terms delayed, retarded or sluggish fermentation are also used on occasion to describe something similar or a variation. However, the focus here is on the possibility of stopping fermentation to resume it later.

This interruption can be achieved with positive cold (without freezing the water present in the dough) or through freezing (in which case we refer to frozen dough). Although both techniques share similarities, they also have significant differences to consider.

Why?

Controlled fermentation entails higher costs as cold application requires energy. It complicates the process, necessitating adjustments and considering new factors, as we will explore shortly. Additionally, there’s an equipment cost involved, as you need sufficient refrigeration chambers to store a significant number of pieces with less turnover than in conventional fermentation.

So, what are the advantages? The first and most obvious is better regulation of bakers’ working hours. In contrast to the more common processes in Spanish bakeries, where bakers must work through the night to offer freshly baked bread in the early morning, controlled fermentation allows breaking this pattern. The baker can work in the afternoon, for example, handling mixing, dividing, rounding, and shaping, then return in the early morning to extract the fully fermented pieces and put them in the oven. This rationalization of schedules offers other possibilities based on very slow fermentations and good organization, but the resulting bread may be different (though potentially of better quality). Another advantage is better production organization, as having chambers where the dough does not evolve allows for better planning. The last advantage is the ability to perform initial operations (mixing, dividing, and rounding) in a larger bakery and distribute the pieces to different locations for fermentation and baking at the point of sale. By centralizing some phases and increasing production, you can negotiate better prices, have better control, better technology, etc., or at least spread these costs over a larger production. Completing the product at the points of sale also presents a more artisanal and locally sourced image.

What’s the Basis?

Yeast has an optimal operating temperature, close to 40°C. As we deviate upwards, we approach their inactivation temperature, causing damage and eventually death. Conversely, as we move downwards from the optimum, yeast activity slows to almost a standstill. To achieve this halt, we must reach the lowest possible temperatures, preferably close to 0°C. However, we must consider that the dough also contains other elements that can degrade it, such as enzymes or other microorganisms. Fortunately, these also slow down significantly as the temperature decreases, more so at lower temperatures.

The most drastic way to stop fermentation is through freezing. Once frozen, the dough becomes very stable, and both microorganisms and enzymes cease their activity. However, yeast is very sensitive to cold, and freezing can damage it. Therefore, it’s necessary to modify the process to reduce these issues. Moreover, the energy cost of storing and transporting frozen dough is much higher than that of refrigerated dough.

When applying refrigeration, it is important to note that the dough, although much more slowly, can still evolve. Therefore, it is crucial to reduce the temperature as much as possible, slightly modify the processes, and carefully consider the time the dough will be refrigerated, as differences in cold rest time can translate into differences in the final product. The advantage of this method is that it’s less harmful to yeast and, therefore, easier to adapt and much less energy intensive.

Considerations

Frozen Dough

The main problem with freezing dough is the yeast’s limited tolerance to cold. It is surprising that a yeast cube can be frozen without much problem, but we cannot freeze dough without losing its fermentative power. This is because yeast is much more tolerant to cold in an initial stage but much less tolerant once it has started to reproduce and ferment. Therefore, before freezing dough, the first thing to do is prevent (or minimize) yeast activity beforehand.

Several techniques can achieve this, such as incorporating yeast in the final stages of mixing, achieving mixing temperatures as low as possible (usually around 20°C), minimizing resting times, and ensuring the time between yeast incorporation and dough entering the freezer is as short and at the lowest possible temperature. It is also possible to use cryotolerant yeast, which has better resistance to freezing conditions, but these are not magical and also suffer. Therefore, we must not neglect the previously mentioned aspects. In some cases, it may be useful to increase the yeast dose, considering that some loss of leavening power will occur.

If we achieve a lower final mixing temperature and lower yeast activity, the rheology of the dough will change. Therefore, if we maintain the same formulation as in conventional baking, the dough will tend to be softer and slightly stickier. To compensate for this effect, we can reduce the dough hydration, use stronger flours, and incorporate additives or enzymes to strengthen the dough. These changes may also require a longer mixing time, as higher-protein flours typically need more time for gluten network development. The advantage is that these doughs will also be more stable against overmixing.

These types of dough are usually frozen in the final piece form, i.e., after dividing, rounding, and shaping. These are low-volume pieces since no fermentation has occurred, and it’s crucial to ensure that the central point has reached a certain temperature (between -7 and -10°C) to ensure freezing. Freezing should be done at the lowest possible temperature, around -40°C. This way, the process is faster, and the ice crystals formed are smaller, causing less damage to the dough. Once frozen, they should be stored at -24°C. Throughout the process, from freezing to final thawing, maintaining the cold chain is essential. Otherwise, ice crystals can melt and re-form as larger crystals, potentially damaging the internal structure and worsening the final bread quality.

Due to the potential problems caused by ice crystals on the gluten network, even with efforts to minimize them, it is often necessary to use slightly stronger flours for these preparations. Reinforcing additives, especially those providing process stability, such as DATEM emulsifiers, can also be very beneficial.

Once frozen, and if the cold chain is maintained, the dough can be transported to stores, supermarkets, hospitality establishments, or final retail points and stored for many months, as it is very stable.

At the point of sale, these frozen doughs must be thawed, preferably at a low temperature to prevent fermentation and maintain control over the process. After thawing, fermentation and baking must follow. These stages should be carried out with the same care and control as in a traditional process.

Refrigerated Dough

Fermentation can also be stopped with simple refrigeration. To do this, we must lower the interior of the dough to the lowest possible temperature without reaching freezing. Although we typically say water freezes at 0°C, this is true for pure water. When there are solutes in solution, such as salt or sugar, the freezing temperature of water decreases, and we can reach temperatures between -2 and -4°C depending on the formulation. To lower the temperature as quickly as possible, we use chambers where the temperature is programmed to 0-2°C. Once we have lowered the temperature of the entire dough, we can slightly increase the resting temperature (to 4-5°C), depending on the circumstances.

It is important to note that, unlike freezing, refrigeration slows down changes but does not stop them altogether. Both yeast and enzymes, as well as other microorganisms, remain alive and can act, albeit at a much slower pace. Therefore, the longer the dough stays in refrigeration, the lower the temperature should be maintained, although in that case, the energy cost will be higher. In many bakeries, dough is refrigerated for only a few hours, in which case a temperature of 4-5°C may be sufficient. However, with good conditions, it’s possible to keep dough refrigerated for up to 72 hours.

Dough is a poor thermal conductor, so the interior of the pieces will take much longer to cool down than the exterior. This can create differences between these areas due to possible fermentation. For this reason, this technique is more suitable for small and flat pieces, where cold reaches the central areas sooner, and less suitable for rounded and large doughs, such as loaves.

In some books, it is advised, similar to frozen dough, to reduce the final mixing temperature. Unlike frozen dough, the temperatures the dough will reach are not as low, and yeast can tolerate them much better. However, it is always good to minimize initial fermentation, both to preserve yeast from slight damage and to avoid the mentioned differences between the internal and external parts of the pieces.

If we reduce mixing temperatures, it will be necessary to modify the formulation and process, similar to what was mentioned for frozen dough. Additionally, besides using stronger flours, we must minimize enzymatic activity since enzymes can act during refrigerated storage. Although they do so at a much slower rate than at higher temperatures, increased amylase or protease activity will alter the final bread quality and may be detrimental. Thus, neither the inherent enzymatic activity of flours nor the enzymes in improvers should be too high. This precaution becomes more critical with longer refrigerated storage times and higher temperatures. For improvers based on enzymes, they must be specifically designed for these processes.

During cooling and subsequent cold storage, it is crucial to be careful with chamber humidity. Most refrigeration systems tend to dry the air and, consequently, the dough. To prevent this, humidification systems are necessary, usually regulated at very high levels, around 90% relative humidity or higher. Another crucial aspect is ventilation, especially door openings. Regularly opening the doors in chambers where refrigerated dough is stored introduces a distortion of the process. When the door is opened, the conditions of the air inside the chamber tend to equalize with those outside. Thus, the chamber temperature will increase, and humidity will decrease. Therefore, door openings should be minimized.

Once the pause is over, the chamber itself can increase the temperature to reach the fermentation temperature. However, it is also possible to transfer the dough from a refrigeration chamber to a fermentation chamber. In the latter case, the temperature change is usually more abrupt and can negatively affect large pieces due to temperature differences between different areas (external and internal). In any case, fermentation times must be defined correctly. If nothing has been modified, it should be noted that the pieces reach the fermentation temperature later than in a normal process (coming from a colder temperature). Therefore, to achieve the same fermentation, fermentation time can be extended, temperature increased, or yeast dosage increased. As you know, there are no fixed rules, and many factors are interrelated, so it is necessary to understand and think through the process.

One last point I would like to mention is that refrigeration can also be applied to unformed dough, so mixing (ingredient reception, dosing, etc.) takes place at a common point, and the dough can be transported to other locations where the process is completed. The refrigeration and humidity conditions will depend heavily on the distances to be covered and therefore the refrigeration times. However, if these times are not high, it should not be very problematic. In these cases, the temperature differences between the external and internal parts are not very concerning because the dough has to be divided, rounded, and shaped again, a process in which it works slightly, and these conditions are equalized. However, all aspects of the process must be studied to avoid losing quality.