Among the processes involved in brewing beer, a large number of by-products are generated. The main wastes produced by the brewing industry include brewer’s spent grains, hot residue, and carbon dioxide. Proper disposal of these wastes brings economic benefits and helps protect the environment from pollution caused by their excessive accumulation.
Although studies have shown that beer contains various functional compounds, the amount of these compounds in beer is diluted due to its high water content. Additionally, the high calorie value and alcohol content of beer limit its health effects. In contrast, brewing by-products may contain a higher concentration of functional components. They can be used as a low-cost and nutritious source of feed and food additives. Moreover, they have the potential to be inexpensive materials for extracting valuable compounds for the food industry.
Distillers grains are the most abundant by-product of beer brewing, accounting for approximately 85% of the total by-product production. Distillers grains consist of barley husks, remaining endosperm starch granules, and other grain additives (such as wheat, rice, and corn) that contribute to beer’s distinctive flavor. Distillers grains are rich in protein, cellulose, and minerals, making them suitable for feeding ruminants. Research has also explored the addition of distillers grains to bread and snacks to increase their fiber content.
The main components of dried hops are fiber, hop bitters, and protein. Dried hops also contain ash, salt, polyphenols, tannins, and oils. The fiber in hops consists of xylose, mannose, galactose, and glucose. Only 15% of the added hops remain in the final beer product, while the remaining 85% becomes spent hops. Although hops are rich in nitrogen, carbon, and protein, their bitter taste limits their application in food. The bitterness of spent hops can be reduced by fermenting them with Candida parapsilosis. After removal, the spent hops can be used as animal feed supplements. Additionally, due to their nitrogen content, hops can be utilized as soil conditioners and fertilizers.
Residual yeast is the second most abundant by-product in beer brewing, accounting for approximately 10% of the total by-products. Carbon is the predominant element in yeast, constituting 50% of its dry weight, followed by oxygen (30–35%), nitrogen (5%), helium (5%), and phosphorus (1%). The protein composition of leftover yeast, distillers grains, and hops is similar, as they all contain essential amino acids, vitamins, and minerals. Therefore, they are commonly used in animal feed and nutritional supplements. However, yeast contains ribonucleic acid (RNA), which is produced during uric acid metabolism, and excessive consumption of excess yeast can cause gout.
Brewery waste finds applications in various branches of the food industry as feed additives and food ingredients. They can also serve as raw materials for extracting compounds used in the food industry or be utilized in biotechnological processes to obtain additives for the food industry.