The reasons why thick porridge becomes thinner after a few mouthfuls may be due to the following reasons:

1. Water evaporation: When cooking porridge, too much water is added It will cause the porridge to become thinner. During consumption, the water in the porridge may be reduced by evaporation, causing the porridge to become thinner.

2. The role of salivary amylase: When we drink porridge, we stir the porridge with a spoon or chopsticks, which may cause the starch in the porridge to be decomposed by salivary amylase, thus making the porridge thinner.

3. Heating temperature and time: When cooking porridge, if the temperature is too high or the time is too long, the starch in the porridge may be gelatinized too high, making the porridge thick. As porridge cools, the degree of entanglement between starch molecules increases, making the porridge thicker.

4. Stirring: During the eating process, if the porridge is stirred frequently, the entanglement between starch molecules may be reduced, resulting in the porridge becoming thinner.

5. Proportion of ingredients: When cooking porridge, different types of rice have different amounts of water absorption. If you add too much water or too little sticky ingredients, the porridge may become thin.

In order to keep the porridge at an appropriate consistency, the following measures can be taken when cooking porridge:

1. Add an appropriate amount of water: Add an appropriate amount of water and adjust the porridge cooking time according to the actual situation.

2. Add sticky ingredients: such as glutinous rice, red beans, taro, etc. These ingredients can help maintain the consistency of the porridge.

3. Use low heat to cook slowly: This allows the porridge to fully absorb water, and also allows the starch to gradually gel and maintain consistency.

4. Heating time control: If the porridge has been cooked, you can continue to heat it for a period of time to allow the water in the porridge to evaporate, making the porridge thicker.

5. Add glutinous rice flour or starch water: Add some glutinous rice flour or starch water before eating, stir evenly and then heat it for a period of time to make the porridge thicker.