Values given in Table 1 show the wide range of CH4 production expected from different substrates. If you look carefully at the specific methane yield results compared to physical and chemical characteristics in the table, you will see that there is a trend. Generally speaking, substrates with OM that is high in energy (high COD:VS), and highly digestible (high percent COD converted) also have high specific methane yields. We might have eliminated Corn Processing Byproduct as a co-digestion product because of its high ash content (only 54 percent VS), but the 54 percent OM that corn processing byproduct contains is highly energetic (3.0 COD:VS), and highly digestible (84 percent COD converted). The resulting specific methane yield (0.26 liters CH4/g VS) is on par with potato peels (0.27 liters CH4/g VS). Potato peel contains much more digestible, but lower, energy OM (100 percent COD converted, 0.64 COD:VS) than corn processing byproduct. These results also tell us something about where to remove substrates from a manure handling system in order to capture the most energy. Compare beef manure removed from outdoor pens to beef manure removed from covered pens (first two lines of Table 1). Both samples have identical VS content, and similar COD:VS ratios. The fraction of COD converted from outdoor pens was roughly 74 percent that of the covered pens, and the specific methane yield was, likewise, 84 percent that of the covered pens. We don’t know how long these two samples lay in the pens, but it appears that the action of wetting and drying of the manure, along with exposure to sunlight, caused some breakdown of manure in the outdoor pens before the samples arrived at the lab.