Spent brewers’ grain as a supplement for oyster mushroom production

Tekstin on kirjoittanut Chris Holtslag Helsieni Oy:stä, joka on kiertotalouteen perustuva, osterivinokkaita paikallisesti tuottava yritys Espoon Kerassa. Helsieni toteutti 6Aika KIEPPI -hankkeessa pilotin Kerassa sijaitsevien panimoiden olutmäskin hyödyntämisestä osana osterivinokkaiden kasvualustaa. 

Helsieni is a circular urban mushroom farm located in the Kera area in Espoo. Helsieni currently produces oyster mushrooms on a substrate of straw and coffee grounds which are pasteurized for a second time before inoculation with mushroom spawn. In 2020, as a part of 6Aika KIEPPI project Nopeat kokeilut, Helsieni initiated a trial using beer mash or spent brewer’s grains as a substrate for growing oyster mushrooms. The goal was to find out if the locally available spent brewer’s grains would be suitable as a supplement in our mushroom production process. The potential benefits that were identified would be higher yields in mushroom production and reduced need for transporting heavy material in and out of the area (both at the brewery and the mushroom farm).

Logistics is a factor to consider when using spent brewer’s grains. Since they are wet (and warm after brewing) they would need to be sterilized as soon as possible after production or  refrigerated if they are to be stored for some days. This adds to the complexity of having to synchronize mushroom production with beer production, and having to wait until the beer mash is available. For small scale production it would be possible to collect the mash in heat resistant polypropylene (PP) plastic buckets.

Left: Substrate with (re)pasteurized beer mash showed some signs of contamination (dark spots). 
Right: unpasteurized supplemented substrate contaminated very quickly.

The research showed that spent brewer’s grains are very susceptible to contamination by other organisms and need sterilization or pasteurization of over 60C for more than 2 hours. Since Helsieni does not currently have the capabilities to do this kind of processes, and it did not seem feasible to include spent brewer’s grains in the mushroom production. If the heat treatment is successful the yield increase would need to be investigated since that was not possible to do in this study.

The scale of the brewery and the mushroom farm is also not likely to be the same. In this case the microbrewery produced a lot more spent grains that the mushroom farm could use, so there would still be a cost of disposing the grains. The disposal cost often includes a fixed element, regardless of the weight. This would negate one of the perceived advantages identified at the outset of the research. For the mushroom farm picking up the mash has a cost (and having the vehicle to do it is not obvious), mainly labor time. For the brewery the cost reduction if all of the waste is not collected, is not significant enough to justify the extra work of collecting some of the mash in separate buckets.

Although these first experiments did not result in a successful continuous use of the beer mash, Helsieni is interested in future experimentation of using the beer mash. A better pasteurization process and clean inoculation needs to be in place, before starting these tests. Also a more detailed analysis of the substrate costs in terms of weight and time in handling in relation to the mushroom growing business needs to be done. The practicalities and routines of handling the wet matter throughout the year need to be addressed. Since the beer mash will need to be re-pasteurized, it would be interesting to know if a cold chain is necessary for the beer mash, or if slight fermentation is beneficial for the oyster mushroom growth.

Other circular economy applications for spent brewer’s grains would be composting it on the  site of or near the brewery. The compost could be offered or sold to local (urban) gardeners, since there will always be a demand for good quality living compost. Additionally, this would be an interesting option for processing all the other biowaste that is generated in the Keran Hallit.

 

You can download the full report and find more information about growing mushrooms at home at www.helsieni.fi.