Alkaline and lye are the same thing.

Alkaline water, also known as lye, or edible alkaline water, is a kind of compound food additive, is a material in the food process, the traditional auxiliary ingredients common in Cantonese-style pastry.

Alkaline water is often added when making the dough for the crust of Cantonese mooncakes. According to the National Standard for Mooncakes, the production of Cantonese mooncakes must use the alkaline water, which is the characteristic method of making Cantonese mooncakes. In the new version of the Standard for the Use of Food Additives introduced on June 20, 2011, this ingredient is not included in the list of food additives allowed to be added.

Expanded Information:

p>In the production and processing of mooncakes, some brands use edible lye water, whose ingredients are potassium carbonate and sodium carbonate. Potassium carbonate and sodium carbonate have similar functions, and their main function is "acidity regulator". There are also some brands that write the word "lye" as "spout". The purpose of adding spout to mooncakes is threefold:

1. To neutralize the acid in the transformed syrup, preventing the mooncakes from having an acidic taste and affecting the flavor and texture;

2. To increase the alkalinity of the mooncake crust, which is beneficial to the mooncake's taste and texture. The higher the alkalinity, the easier it is to color the mooncake crust;

3. Alkaline water neutralizes the acid and produces a certain carbon dioxide odor, which promotes the moderate expansion of the mooncake and makes the mooncake crust more fluffy and less deformed. The main ingredients of the water are also potassium carbonate and sodium carbonate.

Baidu Encyclopedia - Alkaline

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