Kneading is the process by which ingredients are mixed in bakery and the necessary mechanical work to form gluten is provided. Besides these primary functions, there are other essential phenomena that occur during kneading that are important to understand.

Development of Gluten

In the initial stage of kneading, proteins that will later form the gluten network are hydrated. Soluble components, such as salt, dissolve in water and remain in the aqueous phase. If there is oil or fats, they are usually placed between the water and the air bubbles introduced into the dough, stabilizing these bubbles, and facilitating kneading due to their “lubricating” effect.

In the second phase of kneading, the hydrated proteins, through the mechanical work applied during kneading, due to the resistance of these doughs, stretch and intertwine forming a protein network or mesh. This network is responsible for the extensibility of the dough, allowing for the shaping of the dough and the retention of air and expansion during fermentation and baking. If the kneading time is short (less than what’s needed to form this network) it can result in a problem since the dough will be brittle, unable to shape properly, and will have difficulty expanding in subsequent processes. The time required to form the gluten network depends on the type of flour, as well as the other ingredients. In general, stronger flours with higher protein content and higher-quality proteins tend to require longer kneading times. Ingredients with high water retention capacity, such as fibres, also tend to increase kneading requirements. An idea of the necessary kneading time can be obtained through farinographic analysis or similar tests, which we have discussed in the blog before.

If the kneading time is excessive, the gluten network can weaken, leading to lower-quality dough. This weakening can result in stickier dough or reduced ability to withstand prolonged fermentation or the impact of late-stage fermentation. In general, flours with better protein quality tend to tolerate over-kneading without weakening, while flours with lower protein quality are more delicate during this phase. The ingredients in the formula can also contribute to resistance against over-kneading or the opposite effect. Ingredients with high water retention capacity can enhance resistance, while those that weaken the gluten network (sugars or fats) can have the opposite effect, although their effect depends on the type and quantity.

An essential factor in kneading is the type of kneader and the kneading speed. With slow kneaders, such as arm mixers, the kneading time is extended, but problems with dough weakening are reduced. By imparting less energy to the dough, the time required for the dough to weaken the gluten network also increases, providing bakers with more leeway. However, super-fast mixers that can form the dough in less than one or two minutes, especially with low-quality protein flours, can be disastrous if over-kneaded.

It’s also important to consider that the higher the dough hydration, as in the case of ciabatta bread, the longer the kneading time required. Since the dough has less consistency, it also has less resistance to kneading, resulting in less mechanical work communicated to the dough. On the contrary, denser doughs can be formed more quickly due to the higher friction between the kneading accessories and the dough itself.

An extreme case is low-hydration bread typical of some regions in Spain and some Ibero-American countries. Once the proteins are hydrated, they form dough balls, with larger ones having higher hydration. However, these dough balls move within the mixer without receiving additional mechanical work, at least in most mixers. To provide the necessary mechanical work, refining or passing these pieces through two rollers continuously for some time is usually necessary.

Other Processes

In addition to gluten formation, other phenomena begin during kneading. Firstly, all enzymes present in the dough, whether inherent to the flour, or added directly, or with other dough improvers, start to act. If any of the added ingredients also have enzymatic activity, these enzymes will also begin to act during this phase. As you may already know, enzyme activity depends on temperature and pH, so by changing dough temperatures and pH (by adding acids or using sourdough, for example), we can modify the action of these enzymes. One of the enzymes typically found in dough is amylase, specifically a combination of alpha and beta amylases, as we have discussed before. The action of these two enzymes on damaged starch will generate fermentable sugars, mainly maltose, which are necessary for yeast fermentation. It’s also possible that the dough contains strengthening enzymes, such as glucose oxidase, which will strengthen the gluten network through oxidation. However, it is also possible to encounter negative enzymes, such as proteases originating from insect damage to grains. In all cases, we can regulate the action of these enzymes by controlling temperature and pH, but we must be cautious because these changes will also affect other parameters.

Another phenomenon that begins during kneading is the bread fermentation. Yeasts, once dissolved in the dough, usually undergo an initial acclimatization phase where they reproduce through aerobic processes (in the presence of oxygen). This phase is important in various fermentation processes, such as winemaking and beer brewing, and in bread making, it typically occurs naturally. However, the anaerobic fermentation process begins quickly, during which yeasts come into contact with the sugars present in the dough or generated by amylases, producing carbon dioxide and alcohol. These reactions become much more critical during dough resting and final fermentation, even during the initial minutes of baking, but they commence during kneading.

During kneading, air is also incorporated into the dough, laying the foundation for the final structure of the baked goods. Kneading moves the dough, incorporating air, and consequently oxygen. This oxygen facilitates yeast adaptation and all oxidation reactions. Therefore, if there is an oxidizing agent, such as ascorbic acid, it begins to act during this phase (we have discussed oxidizers before). It is important to note that flour pigments can be bleached through oxidative processes. Favouring this oxidation can result in a whiter crumb, while inhibiting it will lead to the typical cream or ivory-coloured crumb. Salt plays an essential role in this process as it acts as an antioxidant, protecting pigments from natural oxidation. Consequently, bread without salt typically has a whiter crumb. A similar effect can be achieved if salt is added in the final kneading stages, allowing oxidation to occur in the initial stages. In Spain, people generally prefer bread with less white crumbs, but in other countries, preferences differ, and they seek bread with very white crumbs. To achieve this, specific oxidizing agents may be used if allowed, or enzymes like lipoxidases. Regardless, by adjusting kneading conditions, you can modify the final crumb colour.

Lastly, we must not overlook the influence of kneading on the alveolation of the dough. The dough’s bubbles are formed during this process, and therefore, the number of bubbles in the dough is determined by this phase. During fermentation, no additional bubbles are created; they only expand as carbon dioxide is incorporated. It is difficult to provide specific recommendations, but the type of kneading machine will influence the distribution of these bubbles. Of course, other factors need to be considered. Doughs with higher hydration will have fewer and more irregular bubbles because the viscosity of the medium surrounding the bubbles is lower, and they may tend to merge, forming larger bubbles. On the other hand, low-hydration bread, like Spanish “candeales,” has a very fine and uniform alveolation. Likewise, the presence of oils or fats in low proportions can help stabilize this structure and facilitate finer alveolation. Special kneading machines exist that allow you to manipulate these characteristics, as we will discuss in a later entry.

Kneading Temperature

One of the most critical aspects during kneading is the dough temperature. This is because most of the reactions that occur, as well as the fermentation process, depend on temperature. Furthermore, the fermentation process is exothermic, and higher temperatures tend to accelerate it. Regardless, the fermentation will alter the rheology of the dough due to gas generation and changes in oxidation-reduction reactions. In industrial processes, regular and homogeneous conditions are necessary (advisable for artisanal processes as well). It is essential to note that dough consistency, stickiness, or lack thereof can affect the subsequent performance of equipment such as dough dividers. Therefore, it is necessary to regulate the final dough temperature.

The final temperature can vary, but it is essential to avoid a significant increase as it can disrupt the process. Generally, a final dough temperature of around 23-25°C is sought. In some cases, it may be beneficial to lower the temperature, such as when the dough will undergo a cooling process afterward, such as controlled fermentation or the production of frozen dough. This is because yeasts, once they have started reproducing, are sensitive to cold, and it is advisable to reduce the previous fermentation processes. However, in general, having a consistent temperature, regardless of the specific value, is more important than having one temperature over another.

The dough temperature depends on several factors, with the most critical being the temperature of the main dough components (flour and water), the temperature of the bakery, and the type of kneading machine. Some kneading machines heat the dough more than others. In general, a straightforward formula is used in bakeries that works well. According to this formula:

Tb = Tf + Tw + Tr

Tf (temperature of the flour) and Tr (temperature of the bakery or room) can be measured, and Tw (temperature of the water) is easily adjustable by altering the tap water temperature. The base temperature (Tb) needs to be calculated for each formula, kneading machine type, how full or empty the kneading machine is, and the desired final dough temperature. By knowing Tb, Tf, and Tr, you can calculate the water temperature, resulting in a consistent final temperature. In some cases, the tap water temperature may not be cold enough, so it is advisable to have a water cooler in bakeries. In other cases, the water temperature calculated using this formula may be below 0°C. In such instances, ice flakes or other methods can be used, but the formula would not be valid because it is based on the specific heat of the ingredients and does not consider phase change heat.

We will discuss the types of kneading machines and other topics related to kneading in a future entry.