Many companies are making efforts to go carbon-neutral, whether out of genuine commitment or spotting a marketing opportunity. The Australian micro-brewery Young Henrys has much bigger goals, seeking to avoid far more warming than their brewing operations create. They’re not there yet, but a collaboration with scientists seeking to slash methane emissions from cows has passed some significant milestones.

Breweries aren't top of the list of greenhouse gas emitters, but “brewing just one six-pack of beer leaves behind a CO₂ hangover that takes a tree two days to absorb,” the University of Technology, Sydney (UTS) note in a media release. Some breweries capture this and use it to carbonate their beer. However, many smaller brewers find the carbon capture technology unsuited to their size, and let the gasses escape, buying CO₂ from elsewhere to feed into the beer, Dr Janice McCauley of UTS, told IFLScience.

In an effort to avoid this, Sydney microbrewery Young Henrys approached McCauley and colleagues. The UTS team’s solution was to put vats of microalgae on the brewery floor and feed them some of the waste CO₂. “It’s like we’re installing a mini-forest on the brewery floor,” said UTS's Dr Leen Labeeuw.

That in itself could make a tiny contribution to keeping the Earth cool, but the collaboration has bigger goals.

In recent years Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO) have shown that certain seaweeds change the microbiota of cattle's digestive systems. In the best cases, this can almost eliminate the methane they produce, currently one of the largest sources of greenhouse gasses. Although some have hailed this as a miracle cure for the problem, there is considerable doubt about how scalable the idea is, given that the most effective seaweeds are rare in nature. On the other hand, “microalgae is very flexible, it can be grown on a small scale using tubular bioreactors in the brewery,” McCauley said, but also has the potential to scale up for larger producers. A single 400-liter bioreactor holds 20 trillion algal cells.

UTS has a large collection of algal types, McCauley told IFLScience. She and her colleagues are searching for those that can match the effects of seaweed, while being grown easily in Young Henry's vats. They narrowed the field first using laboratory assays, and are running the most promising strains through an imitation of a cow's stomach created using real cattles' digestive systems and fed as realistically as possible.

“If this works we will go to a live feeding trial,” McCauley told IFLScience. She added the team are also selecting for algal species with large cell sizes, making them easier to harvest, and capable of tolerating wide temperature ranges and the highest concentrations of CO₂. Then the cows need to like the taste.

If microalgae grown this way prove effective, delivery shouldn't be a problem, at least on a small scale. Like most breweries, Young Henrys already send their spent grain to local farmers who find it provides nutritional benefits for the cows, and can be invaluable during droughts or floods when grass is scarce. Microalgae could easily be added in as a supplement.

The methane cows belch is so much more potent as a warming gas than CO₂ that reducing even a few dairies' emissions could make much more of a difference than simply stopping Young Henry's own gasses reaching the atmosphere. The seaweeds the CSIRO have fed cows, increase their rate of growth, at least when provided in moderation, giving farmers an incentive beyond the environmental benefits. It is hoped the same will be true for microalgae fed on brewer's waste.