Physicochemical composition, fermentable sugars, free amino acids, phenolics, and minerals in brewers' spent grains obtained from craft brewing operations

The unconventional processing of grain ingredients in the craft brewing industry changes the production of brewers' spent grain (BSG) byproducts. This study aimed to investigate the nutritional composition of representative BSG samples obtained from craft breweries in the region of North Dakota and Minnesota in the United States. Whole grain/malt kernels and large fragments were observed in all craft BSG samples which consisted of 38.2% fiber, 33.1% starch, 18.7% protein, 6.3% lipid, and 3.2% ash (dry basis) on average. The limited sparging in the craft industrial processing retained significant amounts of fermentable sugars and free amino acids in the craft BSGs. Fermentable sugars, including maltose, maltotriose, glucose, and fructose, were detected at the total level of 8.2 ± 5.8% in BSG dry basis. Free amino acids in the craft BSGs were at the total level of 2571.7 ± 940.6 mg/kg, with 40% being essential amino acids. Phenolic acids, mainly including ferulic acid, p -coumaric acid, caffeic acid, sinapic acid, and vanillic acid were at the total level of 2309.7 ± 344.0 mg/kg, which primarily existed in the insoluble bound form. The total content of nutritional minerals in the craft BSGs was 1.0 ± 0.2%. The results highlighted that large amounts of starch, fermentable sugars, and free amino acids still remained in the BSGs from craft brewing operations, which should be further exploited. • Spent grains obtained from craft breweries (craft BSG) contain whole grain kernels. • On average, 33% starch and 19% protein were observed in the craft BSG dry basis. • Craft BSG contained large amounts of fermentable sugars and free amino acids. • Up to 99% of phenolic acids existed in the insoluble bound form in craft BSG. • Different craft brewery operations significantly affected the BSG compositions.