Unravelling disposal benefits derived from underutilized brewing spent products in Tanzania

The valorization of raw materials including grain barley, hops, and yeasts, consumption of natural resources like water and energy (heat and electric), use of fertilizers and/or organic substrates, and pesticides in brewing is a global concern. The disposal benefits associated with the spent grain, surplus hops, and surplus yeast is economically and environmentally unrecovered in Sub-Saharan Africa, in which Tanzania is also included. Literature synthesis showed that Tanzania is the 8th worldwide in brewing producing over 4.3 million hL or 430 million litres but depends largely on the imported raw materials such as deficit barley, yeast, and hops. Breweries import 10,500-11,500 tons of barley annually and undocumented quantities of hops and yeast. In the brewing process, every 100 L of beer produces approx. 20 kg of spent grain equivalent to 85% of all by-products hence 15% is for surplus hops and yeast. Much water and energy are consumed in brewing displaying negative impact on these natural resources. In digested surplus yeast H₂S and NH3 gases are released where S and N are nutrients to plants and it has importance as an energy source through biogas. Over 4.3 × 10⁶ hL or 4.3 × 10⁸ L of beer produced in 2016, for example, required total thermal energy of 150,500,000 kWh but only 133,300,000 kWh would have been consumed with the use of biogas as it would have produced 17,200,000 kWh. Total of TZS 36,452,605,000/= or $ 16,129,471 was incurred only in brewing thermal energy but the inclusion of biogas would have saved TZS 4,196,012,000/= or $ 1,843,368 based on the TANESCO tariffs of TZS 242.21/= per kWh. The Government gained over TZS 345 billion as corporate, excise, and value-added taxes. These value addition to disposal options display alternatives to environmental conservation, utilization of natural resources, and overcoming carbon-pint (CO₂) emission into the atmosphere. It is recommended that the significances of these by-products for food, feed, pharmaceuticals, biogas, and soil fertility are scientifically evaluated.