P-23 - Changes in Maillard Reaction Products Due to Heating in Beer Brewing and Their Effects on Koku

The heating process, including mashing and boiling during wort production and kilning during malting, is essential in beer brewing. The Maillard reaction is a chemical reaction between sugars and amino compounds that contributes to the taste, aroma, and color of beer. Maillard reaction products (MRPs) are classified according to whether they react with free amino acids (free MRPs [F-MRPs]) or amino acid residues in peptides and proteins (bound MRPs [B-MRPs]).  

In a study presented at American Society of Brewing Chemists　2023, free, high molecular weight-bound, and total-B-MRPs of seven compounds were analyzed for different types of beer from around the world, referring to previously reported methods, and their relationship to koku (fullness or richness) discussed. The results suggested that MRP values could be used as an indicator of koku. At World Brewing Congress 2024 (WBC2024), 1–3 kDa was found to be the molecular weight range of B-MRPs with the highest correlation with koku. In addition, we previously reported a relationship between boiling time and koku based on 1-3 kDa B-MRPs  and F-MRPs. For the latter, we conducted mashing under two conditions, and in both cases, koku increased with time at 30-120 min of boiling, although koku weakened at 150 min. Some aspects were difficult to explain using the above MRPs under one condition.

In the present study, we re-analyzed the samples reported at WBC2024 after adding a new indicator that showed a relationship with taste, the “browning rate of high molecular weight peptide-bound Maillard reaction products” (Brewing Summit 2025, poster, Ota et al. [browning rate of HMW B-MRPs]). As a result, F-MRPs, 1-3 kDa B-MRPs, and the browning rate of HMW B-MRPs increased with the boiling time, and a strong correlation with koku was observed. From 120 to 150 min of boiling, the tendency of F-MRPs, B-MRPs, and the browning rate of HMW B-MRPs tended to level off or increase, and this trend differed from the decrease in koku. Although the protein content was similar in the range of 30-90 min of boiling, it decreased between 120 and 150 min. In addition, a correlation was observed between the protein content and koku (WBC2024, Poster, Kato et al.), so the decrease in koku in the 150-min sample was thought to be due in part to the decrease in protein content.

These results suggest that the balance and interaction of other substances that change during the brewing process are also important factors; however, MRPs are thought to contribute greatly to koku under certain condition.