From the Internet, a note on bors, which may be helpful: Bors — nothing to do with the Russian beetroot soup of the same name — is the souring agent which gives Romanian soups their distinctive tang and is of ancient Moldovan origin. Bran bors is amber in colour and is supposed to be as clear as possible. It is made by fermenting the protein contained in the outer (bran) layer of wheat in small oak vats. Bors — unlike vinegar and lemon, which can be substituted — is only mildly acid and preserves the flavour of the grain, and therefore can constitute up to half the liquid volume of the soup. Homemade bors is often seen sold in Bucharest markets, but in recent years brand-name bors has also appeared in the shops.
