Activity of individual mash tun peptidases has been estimated under varying pH conditions. Maximum activity at 65° C. for 2 hr. lies between 4-3 and 4–6 pH. In most cases this pH optimum is well defined with activity falling off rapidly on either side of these values. However, the pH optima for the production of glycine, threonine and proline are more diffuse. There is no significant indication that in a malt substrate a second pH optimum occurs in the alkaline pH range.