"Besides a greenhouse, good growers and good protocols are also needed for food-safe production"

"Mapping and standardizing business protocols are becoming an increasingly important issue, both in terms of food safety and operational security. At the same time, a greenhouse is not an autonomously running object. Cultivation in greenhouses and vertical farms is a lot safer than open cultivation, but you still need a good grower to monitor the cultivation and the nursery." That's what crop specialist Tim van Hissenhoven tells us when asked about the risk of a salmonella outbreak in a greenhouse or a vertical farm.

Potential risks
The reason for the question is the outbreak of salmonella in Brightfarms' greenhouse Last week the American grower had to recall several varieties of lettuce. This was despite the fact that during the major e.coli outbreak in the US two years ago, indoor farms and greenhouses were classified as extremely safe. For the open farms, the accessibility of the fields to animals and the vulnerability of the irrigation systems were often mentioned as potential risks.

Business protocols
On CEA farms, incoming water is treated. Rainwater that is used is usually disinfected with, for example, a UV or ozone disinfectant. That already makes the chance of contamination much smaller, experts tell us. Still, there is always something that can happen. A bird flies in through a hole in the insect screen, or the sealing liners on a silo are damaged and what then lies on the ground is not immediately visible.

"Poor follow-up of hygiene protocols by the staff," Tim gives as another possibility. "But it can also come from the substrate in the trays in which the lettuce is grown. In an indoor crop you work much more safely and there is a smaller chance of this kind of contamination, but there is still a chance. And whatever that is, it's a business protocol that's not going well."

He explains that the level of hygiene in horticulture has risen tremendously in recent years, and that America is way ahead of Europe in this. Insect netting, for example, is almost standard there. At the same time, there is still work to be done. It is mainly a matter of mapping out and standardizing the business protocols. When is that silo cleaned, and who is responsible for that, for example. This will minimize the chance of contamination, and if something does happen you can show what you have done: these are the water disinfectors, these are the latest techniques and everything is checked regularly.

Building resilience
At the same time, he also sees that you can't go to 100% sterility. Tim explains that in recent years they have also been focusing on building resilience. It's the same strategy from that of integrated crop protection and administering beneficial bacteria to substrates: not a sterile crop, but a resilient crop, where beneficial organisms keep the invaders in check.

"As a consultant, I did see that in both NFT and hydroponic lettuce cultivation, it is almost impossible to keep a crop completely pure. In addition to standardizing protocols, you're also going to look for some kind of resistance. When you disinfect, for example, you choose a side stream for disinfection, which removes some of the potential pathogens while ensuring that the good bacteria in the water can survive. With proper oxygenation and temperature control, you can prevent your plants from getting sick and continue to grow year-round."

What remains then is testing, testing, testing. Tim: "Part of such a protocol can also be a daily or weekly sampling. Packaging is done here directly from the greenhouse, so there is no extra check from a packer. Contamination can develop in the packaging. By regularly having a sample checked in the laboratory, you have a bit of extra security."