How to Freeze Broad Beans

What are the methods for freezing broad beans? Let's learn how to freeze them.

broad bean

A processing method for preserving broad beans by low-temperature quick freezing. The pre-treated broad beans are quick-frozen at -30 to -35°C or lower, and then packaged in plastic bags, boxes and other containers, or packaged and then quick-frozen, and then stored at -18°C to inhibit the growth and reproduction of microorganisms and the activity of enzymes, so that the broad beans can be preserved for a longer period of time.

How to Freeze Broad Beans

When the water in broad beans drops from the initial temperature to the freezing point below 0℃, it changes from liquid to solid, that is, it freezes. As the temperature drops, the ice crystals increase, and the broad beans become hard and frozen. The freezing point of broad beans varies depending on their species (Table 1). Most broad beans begin to freeze at a temperature of about -1℃. When the temperature continues to drop to about -5℃, 70-80% of their water freezes, and the broad beans become hard. That is, at a temperature of -1 to -5℃, a large number of ice crystals are formed, which is called the maximum formation stage of ice crystals. If the temperature is further reduced to -30 to -35℃, the freezing process is completed. At different temperatures, the water in broad beans has a corresponding freezing rate (Table 2). Therefore, in order to completely freeze the water in broad beans, the temperature must be lowered to the eutectic point, that is, the temperature at which the freezing rate of water reaches 100%.

The speed of freezing of broad beans is closely related to the size of ice crystals and the quality of the product. When broad beans are frozen quickly, many fine ice crystals are evenly distributed in the cells. When thawed, the melted water is absorbed into the tissue and restored to its original state, and the product quality is better; when frozen slowly, large and fewer ice crystals are formed outside the cells. Because the cells are deformed by the pressure of ice expansion, the proportion of cell membrane damage is relatively large. When thawed, the melted water cannot be absorbed into the cell tissue and restored to its original state, causing the tissue to become rough, soft and juicy, thus affecting the quality of the product. Therefore, the frozen broad beans must pass through the maximum ice crystal formation stage as quickly as possible. This method is called quick freezing (usually, the freezing speed is 5 to 20 cm of freezing thickness per hour).