cool veg

eco-cool

On a summer’s day in the UK around 3kWh of energy falls on every square metre of land; great for growing plants but not so great for the picked veg; leave it out in the sun and the shelf life drops.

Although in the past we have had no obvious quality problems caused by leaving boxes on customer’s doorsteps, without shade leaving a box out on a hot summer’s day could have an impact on how long our veg stays fresh. It might not immediately seem like an environmental problem but actually any wasted food represents a waste of all the energy that went into growing, refrigerating and transporting the veg which means all the associated environmental impact was for nothing.

Last summer the focus of our sustainable development project fell on assessing this problem and identifying a low-energy solution.

We took some simple temperature recording devices (about the size of a pound coin) and put them in the core of lettuce in some test boxes, (lettuce is one of the most temperature-sensitive products in a summer box). The results showed that there could be a serious increase in the temperature of veg left out in the sun, which could be wasting all our hard work at the farm. The graph below shows the temperature of a lettuce in a small box left out in the sun last summer.

Satisfied that on a hot day veg could be suffering, we asked The University of Exeter to work out how much of the year this would be a problem. The results came in and we had a summer of covering veg boxes in everything we could think of that might keep things cool without using refrigeration or ice. A quick poll of customers, franchisees and office-staff generated a fairly long list of things to try out:

the solution?

In our efforts to keep veg top quality we covered boxes with wet towels, newspaper, last weeks Riverford box, wooden planks, bits of slate, bits of slate painted white, silver foil, insulation, survival blankets of all sorts, white cardboard, reflective insulation…we even built an evaporative cooler that was effective but not very practical.

One idea that wouldn’t go away was putting boxes in a hole in the ground; not very practical but not a bad idea in terms of low-energy, effective solutions (soil temperature varies much less than air temperature). We came up with the closest practical alternative to encouraging our customers to dig holes in the garden for their boxes, which was included in our trials.

After a fairly exhaustive period of trials we came up with some interesting results; most of the solutions we tried out didn’t work, some just trapped more heat in the boxes.

A seemingly obvious outcome was that shade is the best option. A truly north-facing wall, preferably damp and part of a large building provides good quality shade. Under a garden bench does very little other than take the edge off.

As good shade can be hard to find, we narrowed our solutions down to the most effective, practical solutions and having prototyped them this spring, we have them on offer to customers now.

eco-cool blanket

This lightweight elasticated blanket performed extremely well in our tests, reflecting sunlight away from the box to keep temperatures down. Although not quite as effective as the eco-cool safe (below) the blanket keeps veg up to 5°C cooler and has the added bonus of keeping off rain as well as sunlight. It’s also easy to use and doesn’t take up any space when your box isn’t there.

The blanket fits anything from a mini box up to a large box with a couple of cartons of milk and a few extras. Just squash it inside your used box and your local distributor will cover your new box on your next delivery.

eco-cool safe

It’s a wooden safe, with thick walls and a roof filled with soil, ideally it would be planted with herbs or flowers.

Filled with soil, the safe has ‘high thermal mass’, which means it gets cool at night and warms up inside more slowly during the day as the soil absorbs heat from the sun, keeping the veg put inside it much cooler. Think of a large stone building like a church and it makes sense. Having plants in there and keeping them well watered also improves the way the safe works as water is evaporated taking heat away with it.

This means that in practice your veg stays up to 10°C cooler, which can double the shelf life of your veg.

(Scruff is building these for customers but they do take a little time so we’re rolling them out gradually – we’ll let you know when he reaches your area!).

The graph shows one set of results from testing our prototypes.

You can order your eco-cool blanket either online or by contacting your local distributor.

Riverford sustainable development project

cool veg