The Vietnamese word "lên men" is a verb that means "to ferment." Fermentation is a natural process where yeast, bacteria, or other microorganisms convert sugars into alcohol or acids. This process is often used in making foods and beverages like bread, yogurt, beer, and wine.
In more complex sentences, you might discuss the conditions required for fermentation: - "Để lên men thành công, cần phải kiểm soát nhiệt độ và độ ẩm."
(To ferment successfully, temperature and humidity need to be controlled.)