The amino carbonyl reaction during wort boiling has been examined in relation to the alcohol oxidising activity of the resulting melanoidins. It was found that the amino carbonyl reaction involves 0.23 to 1.56 mM of amino acids and 5.3 to 7.2 mM of reducing sugars per litre. Threonine comprises about 82% of the amino acid involved in the reaction. The main sugars involved in the formation of the alcohol oxidising activity of melanoidins are maltose, glucose and fructose. Increase in the amino carbonyl reaction induced by prolonged boiling of wort results in increased alcohol oxidising activity of wort melanoidins. The melanoidin formation was found to be proportional to the initial concentrations of reducing sugars and amino acids. However, the alcohol oxidising activity of the resulting melanoidins increased with increase in concentration of amino acids and decrease in that of reducing sugars. Increasing wort pH and the addition of phosphates, iron and copper to the wort increase the alcohol oxidising activity of the melanoidins. Addition of sulphite to wort inhibited the amino carbonyl reaction and suppressed the alcohol oxidising activity of the melanoidins.
Keywords: amino acid beer browning carbonyl compound flavour melanoidin stability sugar wort boiling