# Brewer's Spent Grains: Possibilities of Vaporization, a Review
## 2 BSG: A Valuable By-Product  
BSG has a complex chemical composition, which varies according to variety of barley used, harvesting and malting time, and mixing time [8]. Due to the high moisture of the BSG (approximately 80%), shelf life is 7-10 days. Preservation can be done with acids (lactic acid, benzoic acid, formic acid, or acetic acid), which is contrary to the desire of consumers of the most natural food, or can be used in a mixture of benzoate-propionate-sorbate in concentrations 0.2-0.3% (v/v), which can extend its validity by 4-5 days [8]. Drying is considered the most effective method of preservation of BSG. A drying method can be used in two stages--pressing and drying--bringing moisture to 10% [9]. According to studies by [PERSON] et al. (2016), other preservation/drying methods that can be used are:  
* drying in the oven is considered the most suitable but must be carried out at temperatures below 60 \({}^{\circ}\)C, with the disadvantage of a high energy consumption;
* drying by overheated steam in a thin layer brings the advantage of less consumption and improved drying efficiency;
* autoclaving at 121 \({}^{\circ}\)C for one hour has the disadvantage of solubilization of polysaccharides and phenolic compounds;
* drying by freezing with the disadvantage of the need for large storage spaces;  
Figure 1: Barley structure.  
* pressing and filtration through the membrane followed by vacuum drying and drying 2 days in the air to bring moisture to 10% with the advantage that the products in which it was used no longer show microbial growth for 6 months [18].  
Wet preservation can be achieved by adding salt, mixing with pomace, membrane filtration, or vacuum drying (moisture 20-30%) [13]. BSG has high proliferation post-production and for later use must be stabilized and properly stored. For long storage, a moisture of 10% is recommended.  
The chemical composition of the brewer's spent grain is shown in the Table 1.  
Fibers are the components with the greatest interest in health intake (arabinoxylans and \(\beta\)-glucans) but also phenolic components (hydroxycinnamic acid) [8]. Hemicelluloses consisting mainly of arabinoxylan (AX) can be present in up to 40% of the dry weight of BSG (AX is the main non-cellulosic polysaccharide present in cereals and herbs). Another important polysaccharide in BSG is cellulose, and among monosaccharides are found xylose, glucose, arabinose, and traces of rhamne and galactose [8].  
Proteins are found to be around 20% of the dry mass, and the most abundant are hordeins, glutelines, globulins, and albumins. Of the protein content, 30% are essential amino acids, the most present being lysine [8].  
Lipids are found in a low percentage, of which triglycerides have a higher percentage (approximately 67% of total extract), followed by 18% fatty acids, according to [PERSON] et al. (2013) [26].  
BSG also contains phosphorus (6000 mg/kg), calcium (3600 mg/kg), and magnesium (1900 mg/kg) [8; 9], iron, copper, potassium, and manganese [12], and the vitamins present are biotin (0.1 ppm), niacin (44 ppm), choline (1800 ppm), folic acid (0.2 ppm), pantothenic acid (8.5 ppm), riboflavin (1.5 ppm), thiamine (0.7 ppm), and pyridoxine (0.7 ppm) [9; 11; 13]. In addition to all these components are extractives made up of waxes, gums, resins, tannins, essential oils, and other cytoplasmatic components [13].  
It is of interest to separate BSG into individual components due to its high nutritional value and low cost, having applications in both food and non-food industries. When BSG was introduced into the rat diet, it had a beneficial effect on both constipation and diarrhea due to the high content of non-cellulosic polysaccharides, the small quantity of \(\beta\)-glucans, and the content of proteins rich in glutamine [27]. Due to high annual quantity and low cost, it is a source of interest worth exploiting [11].