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Recycling of used brewer’s yeast for environmental protection

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Recycling of used brewer’s yeast for environmental protection

July 27, 2022


Brewer’s yeast used to make beer is usually discarded once it is no longer needed. Sometimes, however, leftover yeast is mixed into livestock feed as a source of protein and vitamins.

Now, there may be even more reason to continue this practice, according to findings from a team of scientists from the Agricultural Research Service (ARS), Warren Wilson College (WWC), and Asheville Sustainability Research (ASR), LLC. of Ashville, North Carolina.

Laboratory results published by the team in the journal Frontiers in animal science suggest that using leftover brewer’s yeast as a feed additive may benefit the environment by helping cows release less methane into the air as a greenhouse gas that contributes to global climate change. Agriculture represents 11 percent of all greenhouse gas emissions in the United States (5,981 million metric tons of CO2 equivalent), with ruminants, including cows, being responsible for more than a trimester of this total.

Methane from cows is a waste by-product resulting from the fermentation activity of certain types of microbes, called methanogens, in the first of the animal’s four gastric cavities, the rumen. Another group of rumen microbes, known as “hyper-ammonia-producing bacteria”, cause the animal to excrete ammonia, a potential air quality problem. and water. The production of methane and ammonia by microbes from the food the cow eats also deprives the animal of the amino acids necessary for growth and milk production, explained Michael Flytheresearch microbiologist at ARS Forage-Animal Production Research Unit in Lexington, Kentucky.

Flythe’s co-investigation into the preventative role brewer’s yeast may play is part of ongoing research effort develop natural alternatives to the use of expensive protein supplements and monensin (a special class of ionophore antibiotics only approved for use in cattle) to control gas-producing microbes. An earlier focus on this front has included the incorporation of red clover into the animal’s diet.

More recently, Flythe teamed up with Robert Bryant (ASR) and Rhys Burns, Christopher Feidler-Cree and Denia Carlton and Langdon Martin – all of WWC – to explore the preventative potential of leftover brewer’s yeast, which ferments the grains used in the manufacture of beer, lager and other types of beer. According to one estimate, the brewing process generates 15 to 18 tons of spent brewer’s yeast per 10,000 hectoliters (or approximately 2,641 gallons) of finished beer, making it the second-largest by-product after spent beer grains (SBG ). According to a 2019 studyEU brewers generate 6 million tonnes of SBG per year and 1 million tonnes of spent brewer’s yeast.

During the brewing process, yeast, known as Saccharomyces cerevisiae, absorbs humolones, lupolones and other hop compounds that contribute to the flavor and aroma of beer. Humolones and lupolones are biologically active molecules that inhibit certain bacteria and other microbes, including those that trigger the release of methane and ammonia from the cow. But until recently, little research had been done on whether leftover brewer’s yeast enriched with hop compounds could be just as effective in controlling the harmful pathways of rumen microbes.

To find out, the researchers took samples of spent brewer’s yeast used to make six different types of beer at a local brewery and added them to flasks containing live cultures of methane- or ammonia-producing microbes. After a 24-hour incubation period, the researchers sampled the gases and analyzed them, observing a direct correlation between the concentration of hop compounds in the spent yeast and the amount of gas produced.

The team also used baker’s yeast and monensin as comparison controls. Not surprisingly, the baker’s yeast, which had not been exposed to the hops during the brewing process, failed to curb the gas production by the microbes. However, spent brewer’s yeast – flush with the hop compounds it had absorbed – curbed the microbes’ methane production by an average of 25% – a reduction comparable to monensin.

Although spent brewer’s yeast is sometimes used as a feed additive for cattle, Flythe said cow-feeding trials would still be needed to fully assess its methane and ammonia reduction potential at scale. the farm.

These results, in turn, should give a better idea of ​​the potential role of yeast as part of a broader, integrated approach to making animal agriculture more environmentally sustainable, Flythe added.