Free Amino Acids Decrease Beer Foam Stability

<p><span>The assumption that “only basic amino acids damage beer foam” is incorrect and should be revised. Beer foam stability has long been discussed mainly in terms of foam-active proteins (e.g., LTP1 and Protein Z) and their loss or inactivation; however, our results demonstrate that foam can deteriorate through an additional and direct route: free amino acids themselves disrupt beer foam stability in the finished-beer matrix. In other words, foam deterioration is not explained only by a decrease in foam-positive proteins—proteolysis products, i.e., free amino acids, can act as independent foam-negative constituents. Importantly, this foam-negative effect is not restricted to basic amino acids.</span></p> <p><span>We first examined a production dataset of &gt;200 lots of a single Japanese pilsner brand manufactured across all factories in 2016 (same raw materials and nominally identical process). NIBEM values differed among lots, and higher free amino acid contents tended to associate with poorer foam stability (lower NIBEM). To test amino-acid-specific effects under practically relevant concentration changes, we quantified, for each amino acid, the across-factory concentration range in the 2016 dataset (ΔC = Cmax − Cmin). Fresh commercial beer (≤7 days after production; 633 mL bottles) from a separate lot was then supplemented with individual amino acids at two levels derived from this real production variability (Level 1 = 2ΔC; Level 2 = 4ΔC), and foam stability was measured by the NIBEM-30 method.</span></p> <p><span>As expected from prior reports, basic amino acids impaired foam stability: lysine and histidine decreased NIBEM values consistently, arginine showed a pronounced decrease at the higher level, and a mixture of basic amino acids also reduced NIBEM. Crucially, several non-basic amino acids likewise decreased foam stability—glutamine, glycine, proline, and γ-aminobutyric acid (GABA) lowered NIBEM values at one or both supplementation levels—demonstrating that foam-negative amino acids are not confined to basic species.</span></p> <p><span>Finally, we show that NIBEM values are highly sensitive to the measurement environment: laboratory ambient temperature substantially influenced the measured collapse time (19 s difference between 20 and 27 °C at constant beer temperature), whereas the temperature of rinse solution used for glass cleaning had negligible impact. Collectively, these findings broaden the mechanistic interpretation of beer foam deterioration by identifying free amino acids—beyond basic amino acids—as direct modulators of foam stability, and they establish strict control and reporting of room temperature as essential for robust NIBEM-based foam evaluation.</span></p> <div> <br> </div>