Treatment of Defatted Soybeans

The main purpose of treating defatted soybeans is to denature the soybean proteins to a form so that it is more suitable for the protease from the starter to digest or hydrolyze (primary denaturation), without the presence of ''native'' proteins (6). However, the soy protein should also not be denatured to an extent that it is not easily utilized by the protease (secondary denaturation.) In order to avoid over-denaturation, the current practice is to steam the soybeans for less than one hour, followed by vacuum cooling to drop the temperature rapidly. The soybeans are also stirred slowly in the cooker to maintain even temperature in order to prevent soy proteins being denatured. This can be achieved by utilization of NK style pressurized rotating steam cooker and vacuum cooling equipment (Fig. 2) (7).

In order to achieve a moisture content of 60-62% in the cooked soybeans, cold water is added at a ratio of 120-130% on a weight basis of the soybeans (i.e., 120-130 kg of water per 100 kg of defatted soybeans). This amount of water is added by spraying the water through tubes inside the cooker with proper rotation of the cooker. After water spraying, the rotation is continued for 5-10 min to allow even water absorption. At the same time of the rotation of the cooker, pressurized steam is injected to 1.8 kg/cm2 and held for 5 min (or 3 min at 2.0 kg/cm2). The cooked soybeans are vacuum-cooled rapidly to 40 °C. In a closed system mode, the cooled soybeans are moved to a sealed mixing tank equipped with a screw-type stirrer and mixed with broken and roasted (stir-fried) wheat, as well as the soy sauce starter (koji).

Another procedure is to inject steam during rotation of the cooker to achieve a steam pressure of 0.9-1.0 kg/cm2 and maintain it for 40-60 min. After cooking, the pressure is reduced with a jet condenser to rapidly cool the cooked soybeans to ambient pressure in 1025 min. When the temperature reaches 40 °C, the broken and roasted (stir-fried) wheat and one-half of the starter (koji) are introduced to the cooker and mixed. This procedure can avoid the introduction of foreign microorganisms and contamination of the batch when cool air is introduced. If the water absorbed by the soybeans is insufficient or uneven, this is a cause of turbid soy sauce (8).

In the past, the cooking process usually took 7 hr at ambient pressure with a large amount of steam. If the soybeans are cooked for only 2-3 hr, are undercooked and the soy proteins are not denatured. It was fairly common to have turbid soy sauce products. Also, in

Figure 1 Flowchart of soy sauce manufacturing.

the past, the soybeans were pressure-cooked with steam at a pressure of 0.7-0.8 atm for 3-4 hr. No matter which way the soybeans were cooked, at ambient pressure or pressurized, the cooked soybeans were left in the cooker overnight. They were taken out the next morning. This procedure will soften the soybeans properly, and the soybeans are suitable for inoculation and making the mash (9).

The use of the NK-type rotating pressurized cooking process does not require the holding overnight period. It can be used for making the soy starter (koji) the same day. The nitrogen utilization rate is much higher than the traditional method, about 83% as compared to 65-70%.

Figure 2 Soybean steamer. 2. Treatment of the Wheat

Roasting (stir-frying) the wheat has the following purposes: it (a) heat-gelatinizes the starch for easy hydrolysis and utilization by the microorganisms, (b) evaporates the water for easy breaking, and (c) kills the foreign microorganisms on the wheat surface.

After selection, the wheat is stir-fried in a flat pan, followed by breaking. For large-scale production, the roasting is conducted in an iron rotating drum (Fig. 3), followed by a roller breaker (Fig. 4). The breaking should achieve a status of 30% passing rate for a No. 30 mesh. This is to avoid contamination during preparation of soy starter (koji) and proper covering of the surface of moistened soybeans. The degree of roasting is to have fox (brown) color on the surface of the wheat kernels, with the disappearance of green odor. The volume of the kernels will increase considerably. Direct roasting is also conducted, avoiding burning or charring of the kernels. The bran should be slightly stir-fried or steam-cooked.

Figure 2 Soybean steamer. 2. Treatment of the Wheat

Roasting (stir-frying) the wheat has the following purposes: it (a) heat-gelatinizes the starch for easy hydrolysis and utilization by the microorganisms, (b) evaporates the water for easy breaking, and (c) kills the foreign microorganisms on the wheat surface.

After selection, the wheat is stir-fried in a flat pan, followed by breaking. For large-scale production, the roasting is conducted in an iron rotating drum (Fig. 3), followed by a roller breaker (Fig. 4). The breaking should achieve a status of 30% passing rate for a No. 30 mesh. This is to avoid contamination during preparation of soy starter (koji) and proper covering of the surface of moistened soybeans. The degree of roasting is to have fox (brown) color on the surface of the wheat kernels, with the disappearance of green odor. The volume of the kernels will increase considerably. Direct roasting is also conducted, avoiding burning or charring of the kernels. The bran should be slightly stir-fried or steam-cooked.

Figure 3 Wheat roaster.
Figure 4 Wheat crusher.
Bread Making

Bread Making

Discover How To Surprise Family and Friends With Homemade Bread? Is Your Bread Coming Out Doughy Or Crumbly? Well, you don't have to be frustrated anymore by baking bread that doesnt rise all of the way or just doesn't have that special taste.

Get My Free Ebook


Post a comment