Sour Mash is a batch of old mash (mash itself is used in the process of distilling) that is being further fermented.[1]
A City doctor might prescribe barley mash applied to the scalp.[2]
The Sour Mash is a lesser punishment given to prisoners of Cragscleft Prison for minor offences. According to the prison log for block one and block three, both Issyt the Beggar and Dikket were fed sour mash during their stay.[3][4]