Food Scraps & Cafes — how much waste is there and could it be composted in a home garden setting?

A couple of years ago I was really curious about just how much food waste was generated in a cafe.

My question — could it all be composted to make soil and then used to grow food for that cafe?

I had a chat with a local cafe owner here in Tuakau — Mich at Sugar Plum Kitchen, who had just recently started putting her food scraps into landfill after a pig farmer stopped collecting them.

It was my lucky day, she was delighted to take part in the research.

I went and got a couple of Mitre10 buckets, and she got her staff to add all the food scraps to the buckets. I’d bring a clean bucket in, swap it with a half-full bucket, which went back to the soil farm for composting.

Over and over and over and over.

I’d often bring in a bunch of flowers ‘grown in cafe soil’, and she would often offer me a complimentary cup of coffee.

Here’s a summary of what I learned:

Trial period: 8th October 2022–13 April 2023

That’s 187 days or 26.7 weeks, or 6 months and six days.

42 visits — this works out to an average of one visit every 4.5 days.

614 litres of food scraps — on average 23.6 litres a week.

For context: the cafe is open for business 7 days a week from 8am-3pm, and 8:30am-2:30pm on weekends.

I accepted all the food scraps — meat, dairy, bread, cheese, vegetables, table scraps.

How I composted it at the soil farm:

Initially I used a compost tumbler, but quickly ran out of space, so I started using big blue food grade barrels. These are 220 litres in size, and I only ever needed two of them. Even though I collected over 600 litres of food waste, it shrank in volume over time.

At the time I began, I was starting to get more intentional about tracking the inputs into my Hua Parakore garden, and therefore wanted to keep this cafe compost separate from the rest of my space.

There came a point where I had enough data to summarise the volume over a good length of time, and without a way to use the compost I was making, it started to feel like voluntary labour that wasn’t ever going to bring about any sort of change, so I let Mich know that if she wanted my help setting up a composting system in her own home garden in Tuakau that I could help her do so.

We’re still friendly, but for now my volunteering time is spent growing flowers across the railway line from the Sugar Plum Kitchen behind the Tuakau Museum, where I can also teach composting, and don’t need to carry waste off site.

Time spent:

24 hours driving backwards & forwards to the cafe (8km round trip)

13.5 hours spent actually making the compost: this included the time needed to wash the bucket and put it back in the car, rip up cardboard boxes or forage for weeds from the garden to balance out the food scraps.

Petrol was costed at 83 cents per km (this rate taken from the IRD website in 2022)

An imaginary processing fee was set at $1 per litre for the food scraps.

The total estimate for the six month trial based at $50 per hour was $3,443.09.

This equates to about $132 per week.

In this scenario, $6 per litre of food scraps would have covered travel time, bucket washing time and fuel expenses for the 8km round trip at a rate of $50 per hour.

Alternatively, selling the finished soil at $10 per litre could have achieved the same goal.

Suggestions for others who are exploring the viability of compost cafe food scraps:

• Minimise the transportation as much as possible. For this cafe in Tuakau, it would be relatively simple to compost it within 100 metres and carry the buckets by hand or bicycle.
• If there really isn’t space to compost onsite, consider partial composting on site, e.g. using in-ground worm farms within flower beds. Food waste has a lot of moisture (and nutrients) and will compact in size as it turns to soil. There’s a good chance that when transportation is required, it could be transportation of half finished compost. This process would also reduce odours.
• I don’t recommend letting food scraps sit for any longer than three days, especially in warm weather. Larger restaurants may require daily pickups.
• I suggest starting off with knowing how the finished soil will be used before starting a trial, so that the composting system can be fully circular from the outset — and to build in the cost (or the time it takes) to deliver and use that soil. I was hopeful that I could grow flowers or herbs for the cafe, but this was not cost effective for the cafe.
• Can the role of composter be created within the context of the organisation, just like cafes with reusable plates and cups have staff responsible for washing dishes? Does a future friendly cafe or restaurant need to train up a team of composters?

I would love to hear your thoughts on this trial. Please reach out to me by email at katrina@blueborage.co.nz with your comments.

Here’s a link to a spreadsheet with the summarised figures that can be used as a ‘compost calculator’ — enter the distance & time to transport the food scraps, the volume of waste per week & the days between collections, the hourly rate for transportation and composting, and see what number it gives you.

To use the file — please make a copy first. The link here gives you access to the document but not editing rights.

And for cafe owners — good luck with your composting!

-Katrina

Ideas for innovative edible gardening solutions using biodynamic methods to make exquisite compost is what the world needs right now. To see the full range of online courses go to www.blueborage.co.nz or get in touch by email at katrina@blueborage.co.nz