When are soft and moist fruits in the refrigerator, or fruit juice with a gassy taste, considered ritually impure (najis) or unlawful (haram) due to their transformation into alcohol?

It is permissible to consume fruits and juice as long as they have not spoiled or fermented. The criterion for prohibition is: that which intoxicates in large quantities, a small quantity of it is forbidden. A small amount of alcohol in juices is overlooked, but if an alcoholic smell or gas bubbles appear, it must be avoided, as this is a sign of the beginning of change. The Prophet, peace and blessings be upon him, used to drink nabidh as long as it was sweet and had not changed or boiled. If its taste changed or a gassy smell appeared in it, it was to be avoided.