|PSZCZOLKOWSKI, VIRGINIA - Warren Wilson College|
|BRYANT, ROBERT - Warren Wilson College|
|HARLOW, BRITTANY - Oak Ridge Institute For Science And Education (ORISE)|
|MARTIN, LANGDON - Warren Wilson College|
Submitted to: Advances in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/14/2016
Publication Date: 8/17/2016
Citation: Pszczolkowski, V.L., Bryant, R.W., Harlow, B.E., Aiken, G.E., Martin, L.J., Flythe, M.D. 2016. Effects of spent craft brewers’ yeast on fermentation and methane production by rumen microorganisms. Advances in Microbiology. 6:716-723. http://dx.doi.org/10.4236/aim.2016.69070.
Interpretive Summary: Ruminants, like cattle and goats, can use the energy in fibrous feeds (e.g. grass) because the bacteria and other microorganisms in the rumen can digest fiber. Most of the products of rumen fermentation are nutritionally available to the animal, but methane is not. The carbon in methane gas is lost to the animal when it is eructated (burped) out into the atmosphere where it is a greenhouse gas. The spent yeast from craft breweries contains a high level of plant secondary metabolites, called hops acids, left over from the hops used to make beer. The hops acids are inhibitory to select rumen bacteria and have favorable effects on rumen fermentation. Rumen microorganisms were collected from cattle and goats and tested in fermentations that contained spent craft brewer's yeast or another yeast that did not have hops acids. The rumen microorganisms made less methane in the presence of craft brewer's yeast. Feeding trials are still needed, but these results indicate that this waste product of the brewing industry could be a valuable co-product for ruminant industries. The impact of this work is in identifying that the concentration of hops acids in the spent craft brewers' yeast adds value.
Technical Abstract: Saccharomyces cerevisiae is a key component of beer brewing and a major by-product. The leftover, spent brewers’ yeast, from large breweries has been used for some time as a protein supplement in cattle, however the possible advantages of spent yeast from smaller craft breweries, containing much higher levels of bioactive hop acids, have not been evaluated. Hops acids from the hops used to make beer primarily end up in the yeast once brewing is completed, and have antimicrobial activity against Gram-positive bacteria. Uncultivated suspensions of bovine rumen microorganisms produced less methane during fructose fermentation when exposed to using inactivated, freeze-dried spent craft brewers’ yeast than a bakers’ yeast control. The experiment was repeated with caprine rumen microorganisms and ground grass hay as the substrate. Total gas production was not inhibited by craft brewers’ yeast, but again, less methane was produced (2.7% vs. 6.9% CH4). Both experiments also revealed a decrease in acetic acid production, but not propionic acid production, when craft brewers’ yeast was included. These results indicated that spent yeast could represent a co-product for craft breweries, and a feed supplement for ruminants that has a favorable impact on methane production.