Cooked white or brown rice can turn grey after refrigeration due to a process called "retrogradation." Retrogradation is a natural reaction that occurs in starches when they cool down and are then chilled in the refrigerator. It is especially noticeable in rice because it contains a significant amount of starch.
Here's how the process works:
Gelatinization during Cooking: When rice is cooked, the starch granules in the rice absorb water and swell, a process known as gelatinization. This is what makes the rice soft and edible.
Retrogradation during Cooling: As the cooked rice cools down, the starch molecules begin to recrystallize and reorganize. This process is called retrogradation. During retrogradation, the starch molecules move closer together and expel some of the water that was absorbed during gelatinization.
Refrigeration Accelerates Retrogradation: When you refrigerate the cooked rice, the low temperature accelerates the retrogradation process even further. As a result, the starch molecules continue to reorganize and recrystallize, causing the rice to turn grey and become harder and drier in texture.
While the grey color and change in texture might not be visually appealing, the rice is still safe to eat. However, the taste and texture may not be as enjoyable compared to freshly cooked rice.
To minimize the effects of retrogradation and keep your rice fresh:
- Eat the cooked rice soon after cooking rather than refrigerating it for a long time.
- If you have leftover rice, consider reheating it by adding a little water and covering it with a damp paper towel to restore some moisture and prevent excessive drying.
Keep in mind that while reheating rice can help with the texture, it's essential to handle cooked rice safely to prevent bacterial growth. Store any leftover rice in the refrigerator promptly and reheat it thoroughly to an internal temperature of 165°F (74°C) before consumption. Avoid leaving cooked rice at room temperature for extended periods, as this can lead to foodborne illness.