Among the processes involved in brewing beer, a significant number of by-products are generated. The main waste products in the brewing industry include brewer’s spent grains, hot residue, and carbon dioxide. Proper disposal of these wastes not only brings economic benefits but also helps protect the environment from pollution caused by their excessive accumulation.
Studies have shown that beer contains various functional compounds. However, the high water content dilutes the amount of these compounds in beer. Additionally, the high calorie value and alcohol content limit the health effects of beer. In contrast, brewing by-products may contain a higher concentration of functional components when isolated. These by-products can be used as low-cost and nutritious sources for feed and food additives. They also have the potential to be inexpensive materials for extracting valuable compounds for the food industry.
Brewing Beer and Brewing By-Products
The brewing process of ordinary beer consists of four main stages: malting, mashing, wort boiling, and fermentation. During beer brewing, three main by-products are produced: lees, hops, and residual yeast. These by-products have limited applications and are mainly used in animal feed in the livestock industry.
Distillers Grains
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.
Hops
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 is made up 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 residue. 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 fermentation with Candida parapsilosis, and the resulting spent hops can be used as animal feed supplements. Additionally, due to their nitrogen content, hops can be used as soil conditioners and fertilizers.
Surplus Yeast
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, making up 50% of its dry weight. Oxygen (30–35%), nitrogen (5%), helium (5%), and phosphorus (1%) are the other elements present in yeast. Leftover yeast, distillers grains, and hops have similar protein compositions, all containing essential amino acids, vitamins, and minerals. Therefore, they find greater usage in animal feed and nutritional supplements. However, excessive consumption of excess yeast can lead to gout due to its ribonucleic acid (RNA) content, which is produced through uric acid metabolism.
Application of Brewery By-Products in the Food Industry
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 applied in biotechnological processes to produce additives for the food industry.
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