The softer the cheese, the more perishable it is. Ripe Brie will keep for just a few days. If the cheese becomes too runny or smells of ammonia, it indicates the cheese has been aged too long. Owing to concerns about Listeria bacteria, the U.S. Food and Drug Administration recommends that unpasteurized, soft, aged cheeses like Brie should not be eaten by children, older people, or anyone with a compromised immune system.