"This was the smallest we could build and still be commercially viable, so it's tight for space," co-founder and chief executive Kate Hofman said of its Beckton site, housed in one of an array of industrial units that gives no external clue as to the cutting-edge production inside. "We designed the system to make the best use of the space and to maximise the yield per square metre."
In production since October, the system combines hydroponic growing under LEDs with aquaculture (fish farming) next door. The waste water from the fish provides a nutrient-rich feed for the plants. With a staff of four "we don't divide labour up in a traditional way - they are multi-skilled and each do everything", Hofman explained. "Someone has to be here seven days a week."
She described the aquaculture units as "standard", with 12 tanks generating an artificial current, and lit by blue LEDs to reduce algal growth. The tilapia fish - a popular species in some ethnic cuisines - are bought in at the fingerling stage and take six months to grow to harvest.
"Tilapia are farmed all over the world. It's a very good protein converter, with a conversion ratio of 1.7 to one, and omnivorous, unlike, say, trout," Hofman pointed out. "But they are a warm-water species so we keep the temperature in the 22-24 degsC range. In theory you could farm any freshwater fish with the right diet and conditions."
Currently the fish are given a standard pelletised feed. "We would like to have an insect-based feed," she revealed. "We are working towards global aquaculture standards."
Waste water from the tanks is filtered in agitation tanks filled with plastic pellets that are home to bacteria that convert the nitrates to nitrites, then passed to the hydroponic unit next door. "We have had to bring in a lot of stuff, including from the US and biofilters from Scandinavia," said Hofman, costs that have added to the initial outlay but are likely to drop as the techniques become more established in the UK.
Next door the hydroponic unit has 10 levels, each with a Philips LED lighting recipe tailored to the individual crop, ranging from pea shoots to basil. "The things that grow well are leafy greens that use a lot of nutrients," said Hofman. "We could grow strawberries but would need to supplement the nutrition to get the flavours."
GrowUp has not yet undertaken nutritional analysis of its crops. "It would be interesting to know," she said. "Since it's a controlled environment, we can add in anything that's needed to rebalance them."
The LEDs have filters to bring them closer to the daylight spectrum, to suit the workers rather than the plants, she explained. Perforated ventilation tubes along the side of each unit ensure air circulation, minimising the opportunity for moulds to take hold.
"The main issue is humidity. We use no chemicals or pesticides but we do have an integrated pest management strategy. We are mostly concerned about aphids, but the growing medium is warm, damp and filled with fish poo, which attracts flies that aren't interested in the crop."
Seeds are germinated in situ in a substrate made from recycled carpet fibre. "In a larger unit you would have separate germination units. We would consider that for future installations," she said.
Everything is grown to order so the shelves are not always at full capacity. Deliveries are made by electric van within 12 hours of harvest. "There are some crops we can get to harvest in seven days."
Until the Whole Foods deal, restaurants have been the main market. "We have very positive feedback from chefs. The shelf life is fantastic. We say five days on the pack but we have kept pea shoots for three weeks without deterioration.
"The fish are not a big earner. This unit was sized to suit the hydroponics and so we haven't worried about efficiency. To be efficient we need to be larger. We would like to work at five or 10 times this size. That would allow a lot of automation, though employment is part of what we do."
Indeed, some start-up funding has come from social enterprise funder Ignite, which seeks social and environmental as well as commercial returns, as well as from the Government's Agri-Tech Strategy. "Now that we have this up and running we have had a lot of interest from more traditional investors in doing something larger," said Hofman, adding that she expects the company to make such a move "within the next 18 months".
The estimated return on investment for the current unit is eight-to-10 years. "With bigger farms that would be less, but they would probably have to be further out of town. This will always be where we bring people and trial new things."