Refrigeration plays an important part in all stages of modern bakery production from the preservation of raw materials such as flour and yeast to the cooling of finished dough. Flour is usually stored in bins in air-conditioned spaces at ambient temperatures. It is important to filter the flour dust in the air since it may settle on the heat transfer surfaces of the air-conditioning system and reduce heat transfer. Yeast is dormant at temperatures below 7°C, and thus it is stored in refrigerated spaces below 7°C but above its freezing point of 3.3°C since freezing kills most cells. Yeast is most active in the temperature range of 27 to 38°C, especially in the presence of nutrients such as sugar and water, but temperatures above 60°C must be avoided since yeast cells cannot survive at those temperatures. Ingredients such as corn syrup and liquid sugar are stored in heated tanks at about 52°C to prevent thickening and crystallization. The first step in the preparation of baked products is the mixing of flour yeast, water, and other ingredients, depending on the kind of product, into dough. \The temperature of the dough tends to rise during mixing as a result of the heat of hydration, which is the heat released when dry flour absorbs water, and the heat of friction, which is the mechanical energy supplied to the mixer by the motor. Therefore, cooling is needed during kneading of the dough. The easiest way to maintain the dough at the desired temperature of 26 to 27°C is to cool the water to 2 to 4°C before mixing it with the other ingredients. Another method is to cool the mixing chamber externally with water jackets. After mixing, the dough is allowed to ferment in a room maintained at about 27°C and 75 percent relative humidity for a period of 3.5 to 5 h. The dough temperature rises by about 5vC during fermentation. Some water as well as other fermentation gases such as alcohols and esters evaporate from the dough surface, and the rate of evaporation depends on the relative humidity of the environment and the air velocity. The dough is formed into loaves and is kept in an enclosure at 35 to 49°C for about 1 h. The fully developed loaves are then baked, usually in gas-fired ovens at 200 to 230°C for 18 to 30 min, depending on the type of bread. The hot air in the oven is circulated to ensure uniform baking. The exposed surfaces of the loaves are sprayed with steam to caramelize the sugars on the surface at early stages of baking to obtain a gold-coloured crust. The temperature of the baked loaves is about 95°C inside and 230°C on the crust. The baked loaves are allowed to cool in racks to about 32 to 35°C, which takes about 1.5 to 3 h before they are bagged and shipped. The cooling time can be shortened by using forced airflow. The cooling rate is high initially because of the large temperature difference between the bread and the ambient air and the evaporative cooling due to the vaporization of the moisture in the bread.

Bread starts losing its freshness shortly after baking as a result of the starch crystallizing and losing moisture, producing a crumbly texture. A tight wrap can slow the process by sealing the moisture in. Bread freezes at about 8°C.

To preserve quality and to keep the cellular structure intact, the bread must be cooled as fast as possible; Wrapped bread loaves can be cooled from an internal temperature of 21°C to 10°C with cold air at 29°C and 3.5 m/s in about 3 h. Unwrapped bread will freeze faster, but the moisture loss in this case will be excessive. Frozen bread can be defrosted at room temperature with satisfactory results.