## 4 Discussion
[39], malt words obtained from barley were characterized by an FAN content of 63.2 mg\(\cdot\)L\({}^{-1}\), while the values were 78.9 mg\(\cdot\)L\({}^{-1}\) for oat, 85.2 mg\(\cdot\)L\({}^{-1}\) for rye, and 90.9 mg\(\cdot\)L\({}^{-1}\) for wheat. A similar difference between FAN contents in barley and malt wort was also reported by [PERSON] et al. [42], showing a lower FAN level in barley word (57 mg\(\cdot\)L\({}^{-1}\)) than in malt wort (160 mg\(\cdot\)L\({}^{-1}\)). In the research by [PERSON] et al. [43], the wort in 100% barley malt was characterized by an FAN content of 107.1 mg\(\cdot\)L\({}^{-1}\), while the values were 69.7 mg\(\cdot\)L\({}^{-1}\) in 77.5% barley malt + 22.5% unmallated oat, 65.8 mg\(\cdot\)L\({}^{-1}\) in 100% oat malt, and 45.4 mg\(\cdot\)L\({}^{-1}\) in 77.5% oat malt + 22.5% unmallated oat. Free amino acids are essential in the fermentation process, mainly for yeast metabolism, and significantly affect the quality characteristics of beers, including the stability of the beer head or the sensory qualities of the final product. During fermentation and in the final product, some amino acids are converted into aldehydes. In order to delay the ageing processes of the beer and the deterioration of its quality, it is recommended that the content of free amino acids in the finished beer be relatively low [44; 45]: the higher the protein content of the wheat malt used for beer production, the lower the polyphenol content of the final product after the fermentation process [46; 47]. Chemical compounds that are important for the taste of beer are formed through interactions between carbonyl compounds, esters, sulphur compounds, alcohols, phenolic compounds, or organic acids [10]. The beer head is one of the most important attributes influencing consumer appeal and consumers' decisions to reach for a specific beverage range in the future. Wheat beers should be characterized by a long-lasting abundant head with high saturation [48]. The quality and stability of the beer head are significantly influenced by the proteins in the malt that enter the word during mashing. Glutenin and gliadin (wheat gluten proteins) are converted into high-molecular-weight water-soluble proteins during malting which affect the foaming properties of beers and their haze, especially when interacting with polyphenic compounds [11; 12]. During boiling and in the final stage of fermentation, the protein content of the word is stable, while the greatest decrease in protein content occurs in the initial stage of the fermentation process. The addition of wheat malt to beer production (raw material) positively influences the stability of the beer foam due to a higher proportion of soluble proteins. Wheat malt is also characterized by a high proportion of high-molecular-weight proteins, which are responsible for foam stabilization. Proteins derived from barley malt are responsible for the construction of foam particles [14]. Significant research attention has been paid to the LTP1 protein responsible for lipid transfer and the \(Z\) protein, both of which have an important influence on beer foam formation and stabilization [49; 50]. In their study, [PERSON] et al. [49] found that a protein fraction of 2.1-7.6 kDa contributed most to beer foam, while a protein fraction of 13.2-100.0 kDa was responsible for beer quality characteristics.