The amount of alcohol in kombucha tea is a very low amount that does not lead to drunkenness, hence drinking it is not haram because of that. For more, please see the detailed answer.

Drinking alcohol is a major sin, for wine is the mother of all evils. It clouds the mind, wastes money, causes headaches, tastes foul, and is an abomination of Satan’s handiwork. Allah has cursed the drinker of alcohol. The Prophet (peace and blessings of Allah be upon him) likened the one who is addicted to alcohol to one who worships idols.

Zina, alcohol and gambling are all major sins. The most serious of these three major sins is zina. The basic principle is that zina is the worst of the three, then alcohol, then gambling. But it may vary according to the evil consequences that result from it.

It is not permissible to sell, buy or drink intoxicating beer. Scholars have ruled that non-intoxicating beer is permissible because it is completely free of alcohol, or because it contains a minuscule amount of alcohol.