Cold brew coffee phenomenon producing possible turfgrass fertilizer

Writer: Kay Ledbetter, 806-677-5608, [email protected]
Contact: Dr. Ben Wherley, 979-845-1591, [email protected]
Garrett Flores, [email protected]

COLLEGE STATION – From the coffee maker to the lawn, investigators in a Texas A&M AgriLife Research study are scattering spent coffee grounds on turf plots to see if the beverage leftovers can give the grass a jolt like the drink does for its consumer.

Dr. Ben Wherley, Texas A&M AgriLife Research turfgrass ecologist in College Station, said the two-year study will determine if the used coffee grounds can serve as a replacement for some of the currently used top-dressing fertilizers and soil amendments.

Wherley and his master’s student Garrett Flores will compare fresh and composted grounds to other organic and synthetic fertilizers and sphagnum peat moss, which is commonly used as a soil amendment in sand-based sports fields and golf course putting greens.

The study was discussed at the recent Texas A&M Turfgrass and Landscape Field Day. The study plots are located at the Scotts-Miracle Gro Center for Lawn and Garden Research at Texas A&M, located off F&B Road in College Station.

The work has been partially supported through a seed grant from the United States Golf Association Green Section as well as GeoJava, a new eco-friendly company started by Chad McNair, CEO of Aspen Beverage Group in San Antonio.

“We think this might provide a nice alternative by using a spent resource and not cutting into a non-renewable resource like peat moss,” he said.

What’s really brought increased interest in this is the explosion of cold-brew coffee, Wherley said.

He said Aspen Beverage Group is providing a substantial supply of spent coffee grounds for the project, which is trying to find uses both as a surface application, perhaps as a fertilizer or compost, but also as a soil root-zone amendment in sand-based systems.

Aspen Beverage is a cold-brew coffee company, one of the largest in North America, and produces about 40 cubic yards a day of spent coffee grounds. That’s enough to fill a dumpster 22 foot long by 7.5 feet wide by 8 feet high.

“And they expect to be up to 250 cubic yards a day by next year,” Wherley said. “We are trying to help them find an environmentally friendly and economical way to use these coffee grounds.”

Wherley said in the past it might not have been feasible or practical to do this type of research based on the widespread and limited amounts of spent coffee grounds available. In fact, during the grant application process, he said he was asked “if we were going to go around and pick up a 5-gallon bucket of grounds every day.”

But the coffee scene has changed, he said.

“Cold brew is all the rage because college students find it doesn’t have the acidity of normal coffee and they like the texture and flavor,” Wherley said. “So people who haven’t been drinking coffee in the past are now drinking it, and it is replacing the energy drinks.

“The sheer volume being provided by not only Aspen but other cold brew extractors around the U.S. provides a new material we need to look at a little more closely for agronomic systems. There’s a need to use these or get rid of them in some fashion.”

He said a second benefit in determining their nutritive value to turfgrass and keeping them from going to the dump is the reduced amount of synthetic fertilizer used on lawns.

Flores said they have 10 different treatments under study, including an untreated plot. Coffee grounds tested are both fresh and composted. The composted coffee grounds analysis indicates they have a slightly higher nutrient level.

The spent coffee grounds have about a 2.5-3 percent nitrogen content, and a carbon to nitrogen ratio of about 20 to 1, which could theoretically make them fairly desirable for fertilizer application, Wherley said.

“Cold brewing is a very slow process which substitutes time for temperature in the extraction process,” he said. “Coffee is very complex with over 1,000 compounds. When cold water is used to brew the coffee, some of the compounds that come out at higher temperatures are left in the bean. These are the fatty acids and oils that can cause bitterness.”

The result of cold brewing is a coffee with less than half the acid of hot brewing, making cold brew very smooth. This smoothness makes it possible, even desirable to drink cold-brew coffee at about twice the strength of regular hot-brewed coffee, which means twice as much coffee and twice the caffeine per ounce, Wherley said.

“When we have tested hot-extracted coffee grounds and cold-brew grounds, our experience is the cold brew grounds still have more ‘juice’ or nutritive qualities. It leaves a lot of material in the grounds, so it might prove better in the long run.”

He said regardless of which coffee grounds are used, if they are dried, they spread very easily out of a rotary spreader, so the application is quite feasible. GeoJava has been working with local landscapers in San Antonio that have been doing top dressing applications for many years.

Flores said in the study they are comparing the coffee grounds to both slow- and quick-release fertilizers to determine how they compare. Varying rates of poultry litter-based organic fertilizer, ammonium sulfate and sulfur-coated urea are being tested.

“We are primarily evaluating growth, turf quality and color,” Flores said. “We will evaluate turf color using digital imaging software. We will also take clippings to determine growth rates, as well as the amounts of nutrients that are absorbed.

“We are also tracking soil moisture in the plots,” he said. “We are going to see whether coffee grounds increase the moisture retention ability of the soil.”

Flores said additionally they will be evaluating changes in the soil microbial biomass due to spent coffee grounds as well as other fertilizer treatments.

“The coffee grounds provide considerable organic matter and we will be determining how readily the microbes are able to break it down into a usable form of fertilizer for the plants to take up,” he said.

“We’ll be following this study over the next two years to evaluate turf health and performance and see whether there is potential for a marketable end-use for spent coffee grounds,” Wherley said. “As we see an increased use of cold-brew coffee around the country, it would be nice to be able to utilize these in an agronomic setting.”