Baking

What is Baking?

Baking is the final step in making yeast-leavened (bread, buns, rolls, crackers) and chemically-leavened products (cakes, cookies). It’s a thermal process that uses an oven, which transfers heat to the dough pieces via:

• Conduction through heated surfaces
• Convection through hot air
• Radiation from heat sources such as flames

The heat in turn activates a series of physicochemical changes, responsible for transforming the raw dough into a baked good with a firm, dry crust and a soft  crumb.

Origin

Baking is probably as ancient as human kind. The first civilizations in recorded history, the Egyptians and Mesopotamian people, cultivated wheat. They learned the art and craft of baking bread after discovering that wheat kernels could be eaten in a palatable form by grinding and turning them into flour, and then adding water to create paste which could be cooked and consumed. At the time, fire and manual work were key for the development of primitive baking processes.¹

How does it work?

Baking sets the final structure to baked goods. It involves simultaneous heat and mass transfer phenomena. The heat travels from the surrounding air into the interior of the dough or batter while moisture and other liquid compounds travel/escape from the core towards the exterior or surrounding air due to evaporation.²

While both yeast and chemical leaveners can result in gas development and volume build-up, yeast is essential for the development of unique flavors in breads and some baked goods.

Baking of yeast-leavened bakery products (dough-based systems)

Coming out of the final proofer, the bread dough is well aerated with a typical internal temperature close to that of the proof box, around 35°C (95°F). As the dough pieces enter the oven, their surface temperature begins to increase and heat transfers slowly towards the core of the product. The oven temperature can be set, according to the type of product being processed, at any point between 200–300°C (390–570°F).

In general, there are three major stages in the baking process: expansion of the dough, drying of the surface, and crust browning. These can be subdivided into the following stages (in the order of temperature increase):^2,3,4

1. Formation and expansion of gases (oven spring). A rapid rise in volume takes place at the beginning of baking at a core temperature of 35–70°C (95–158°F). This rise creates the oven spring. Five events occur simultaneously to produce the oven spring in the first 5–8 minutes of baking:
   • Yeast reaches its maximum fermentation rate and generates carbon dioxide, CO₂ gas (CO₂ is also produced by chemical leavening).
   • Release of carbon dioxide gas from the saturated liquid dough phase into the surrounding gas cells.
   • Expansion of the gasses trapped in cells (nitrogen from air and CO₂) and generated during mixing, makeup, and proofing.
   • Evaporation of water/ethanol mixture.
2. Killing of yeast and other microorganisms. This usually occurs at an internal temperature of 60–70°C (140–160°F) where the cells can no longer contribute to the gas production or volume increase.
3. Gelatinization of starch. At 76°C (170°F), starch begins to  gelatinize as granules become fully swollen with local free water. Thanks to starch gelatinization and protein denaturation, the dough is converted into bread and a structure is set.
4. Coagulation/denaturation of gluten (egg or other) proteins that make up the continuous phase. From 60 to 70°C (140 to 160°F), the proteins begin to denature. As a consequence, gluten becomes increasingly tough and stiff as it irreversibly forms a gel. Moisture loss also imparts rigidity to the product being baked.
5. Inactivation of enzymes in the dough (naturally-occurring or added) at 80–95°C (176–203°F).
6. Crust formation and browning (non-enzymatic browning reactions and caramelization). Maillard browning takes place above 105°C (220°F) and requires the presence of a reducing sugar together with an amino acid. Sugars caramelize at 160°C (320°F).

Baking of chemically-leavened products

In this case, the three stages of baking (oven spring, setting of structure and crust formation/coloration) can undergo changes in response to differences in type and amount of ingredients in formulation. Chemical reactions and physical transitions during heat processing may be affected by:

• High content of water in system (hydration of flour and other dry ingredients) which creates a liquid or fluid batter.
• Flour to sugar ratio (high ratio cakes contain more sugar than flour). This has a big impact on starch gelatinization, protein coagulation and water evaporation. Low flour content also requires higher levels of structure building ingredients such as whole eggs.
• Rich formulations (higher content of soluble solids such as sugars, fat, etc.) that shift the system towards an aerated oil-in-water emulsion known as batter.
• Absence of yeast but presence of leavening acids and bases that can modify leavening reactions and these require specific conditions of temperature and available water.
• Modification of pH due to the presence of chemical leaveners which can affect final color of crust/crumb and taste of finished product.

The baking process is responsible for major weight loss in the dough/batter, mainly moisture (8–12%) and volatile organic compounds, especially in pan breads and buns. Chemically-leavened products may have higher bake losses.² For labeling purposes, the loss in weight during baking is taken into account during dough dividing or batter depositing.

The main parameters involved in the baking process include: time, temperature, humidity, air flow (convection systems) and heat flux. These process variables are a function of the size, unit weight, formulation, water absorption, type and target characteristics of the finished product. Baking times may range from 2–60 minutes, depending on the type of oven and heating pattern.

References

1. Walker, C.E., and Eustace, W.D. “Wheat Processing” Encyclopedia of Food Grains, vol. 3, Elsevier Ltd., 2016, pp. 299–304.
2. Fellows, P.J. “Baking and Roasting.” Food Processing Technology; Principles and Practice, 4th edition, Woodhead Publishing, Elsevier Ltd., 2017, pp. 733–752.
3. Gisslen, W. “Basic Baking Principles” Professional Baking, 7th edition, John Wiley & Sons, Inc., Hoboken, New Jersey, 2017, pp. 93–101.
4. Figoni, P. “Overview of the Baking Process” How Baking Works, 3rd edition, John Wiley & Sons, Inc., 2011, pp. 34–44.