When Yeast Goes Down the Drain

Written by on September 12, 2014 in The Beer Diaries



In the process of fermenting beer, whether on a large commercial scale or as a homebrewer, there is always leftover yeast in the form of a sludge at the bottom of the fermentation vessel. This is referred to as spent yeast, yeast slurry, or trub. Most homebrewers either dump this outside or send it down the drain without much consequence. Commercial breweries, on the other hand, are subject to more scrutiny. Two craft breweries in Austin received substantial fees for a heightened level of BOD (Biochemical Oxygen Demand) caused by “improper yeast disposal”. Both breweries were sending their spent yeast down the drain. This brings up a couple of questions. What are the concerns with dumping trub down the drain? What organization was issuing the charges, and why? And what does proper yeast disposal look like?

The Clean Water Act, enacted in 1972, established pollution control programs such as setting wastewater standards for industry. These standards include requirements and standardized measurements for BOD levels and Total Suspended Solids (TSS), among others. This law applies to breweries that dispose of their yeast in public water systems or bodies of water to which the Clean Water Act applies. Some breweries dump their yeast slurry into the drain. While this is a common practice, brewers should beware, unless that brewery’s drains lead to a large septic.

Because decomposition of yeast requires oxygen, dumping spent yeast down the drain in most water systems or bodies of water will increase the BOD of the water. The increased BOD creates an oxygen shortage for other organisms in the water and can throw off the delicate balance of associated ecosystems. Another concern of dumping yeast sludge into water systems is that the yeast increases the TSS in the water which is costly to treat and remove from wastewater. For two breweries in Austin, this increased cost was passed along in the form of a $5,000 charge.

It would be legal under the Clean Water Act to send the spent yeast to a landfill, but adding liquid waste to landfills is wasteful and illegal in some states. The Brewers Association has some recommendations in their sustainability guide regarding best practices for disposing of yeast. Among these best practices is to use an old fermentation vessel no longer in use to hold it until a farmer can pick it up. Yeast is high in protein and can be used as a food additive for livestock. Yeast can also be used to make bread or vegemite for human consumption. Independence Brewery in Austin, Texas has been considering using their spent yeast with vermiculture (worm farms). Microbial Earth is a company attempting to use yeast as a spray to speed up the composting process. Brewers can also implement filtration systems to separate the solids from the liquid yeast before disposing of it as a solid.

There are many ways to properly dispose of yeast besides sending it down the drain. This is an important consideration for small breweries and it is better to put a system in place that they can grow into rather than be faced with charges relating to improper yeast disposal. Besides facing potential negative financial ramifications, it is also better for the environment to not send yeast down the drain. In the next few years I expect more companies to come along finding new ways to use spent yeast effectively – turning one industries waste into something useful and saving it from drain disposal.



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