Money Down the Drain?
here are many issues to worry about when operating a distillery. One of these is the non-fermentable materials that are left after fermentation. In some of my previous articles, I’ve talked about ways to add value to and utilize your spent grains. In this piece, I will talk about issues related to sending the non-fermentables down the drain for the municipal water treatment plant to deal with. A rule of thumb commonly used in the industry states that for every 1 kg of cereal grain used for fermentation, approximately 1/3 kg of each of the constituent product streams (alcohol, CO2, non-fermentable residues) will be produced. On a more scientific basis, the rule of thirds arises due to the metabolism of the yeast while they consume the glucose in the grain’s starch: 1/2 C6H12O6 (Glucose) C2H5OH (Ethanol) + CO2 (Carbon Dioxide)
Theoretically, one bushel of cereal grain can yield a maximum of about 2.97 gal/bu (0.44 L/kg). Realistically, however, an alcohol yield between 2.50 to 2.74 gal/bu (0.37 to 0.41 L/kg) is more common at many distilleries, although some plants can achieve up to 2.80 gal/bu (0.42 L/kg). Thus, 25.4 kg of cereal grain will typically produce about 8 kg of alcohol, 8 kg of carbon dioxide, and 8 kg of spent grains (not counting the water). This equates to a cerealgrain-to-distillers-grains conversion of about 0.30 kg spent grain / 1 kg cereal grain (with a range from 0.28 to 0.32 kg / 1 kg cereal grain) — thus the rule of thirds. Potential variations in cereal grain conversion and fermentation will substantially affect the quantity of coproducts that are generated during processing. Moreover, at individual distilleries, variations in raw material inputs, equipment used, and operational procedures will also result in conversion rates that will not match values found in literature, but instead vary over both time and location. As I have discussed in previous articles, there is much economic value to be gained from dewatering the TABLE 1: spent grains (i.e., separating the thin (TS) (%, dry basis) stillage, which TYPICAL contains water and PROPERTY VALUES dissolved solids) and Dry Matter 5.0 selling the distillers Protein 16.8 wet grains (i.e., Fat 8.1 suspended solids) Carbohydrates as livestock feed. Neutral Detergent Fiber (NDF) 11.7 Typical nutrient compositions for Starch 22.0 thin stillage and Ash 5.9
chemical properties of THIN STILLAGE
Considerations for Byproducts vs. Coproducts vs. Waste Products from Alcohol Distilling WRITTEN BY KURT A. ROSENTRATER
chemical properties of DISTILLERS WET GRAINS (DWG) (%, dry basis)
30.9 - 35.5
25.0 - 39.5
8.5 - 14.5
Carbohydrates Neutral Detergent Fiber (NDF)
39.4 - 58.1
Acid Detergent Fiber (ADF)
23.4 - 25.3
4.6 - 9.0 1.2 - 2.4
The magazine for craft distillers and their fans.