Prepacked salad leaves have been associated with many outbreaks of food-poisoning bugs, including E coli, salmonella, norovirus, campylobacter and cryptosporidium. In July last year, more than 150 people in the UK became infected with E coli after eating prepacked rocket leaves; two died. We eat salad leaves raw, so potentially lethal bacteria (pathogens) aren’t killed off by cooking. More worrying still, researchers have shown that these pathogens can become more virulent once refrigerated. As Hugh Pennington, emeritus professor of bacteriology at Aberdeen University, puts it: “It is safer to eat a burger than the salad that goes with it.”

Ever wondered why your “fresh” leaves so rapidly become flaccid and lifeless after you open the puffy “pillow pack” bag? They’ve been flushed with a mixture of gases known as “modified atmosphere”, which keeps them looking fresher longer and extends their shelf life. Check the packaging closely and in the small print you’ll find a label that says: “Packaged in protective atmosphere.” This isn’t true field-to-fork freshness. It’s perfectly possible that your salad leaves are a week or more old when they reach their “use-by” date; that’s why they slump when exposed to natural air.

Ready to eat
Don’t think for a moment that your supermarket leaves have been hand-washed in sparkling fresh mineral water by vestal virgins. For fresh-produce processing companies, “cleaning” consists of tearing up the leaves and sloshing them around in a Jacuzzi-style tank of tap water that has often been dosed with chlorine. In some salad-washing operations, the same tank may be used to wash multiple batches of dirty leaves over several hours without a water change. After which the fragile leaves are spun or blow-dried in a machine.

When salad leaves are separated from their roots and stems, they become what’s known as “wounded” tissues and deteriorate more rapidly than they do in whole lettuces. This diminishes their vitality and nutritional value. With the exception of watercress, salad leaves aren’t a terrific source of vitamins and trace minerals anyway. You’d be better off eating more micronutrient-rich vegetables such as broccoli, cabbage, carrots and peas.

In Britain, 40% of the salad leaves we buy end up in the bin, according to Wrap, the government’s waste advisory body. That stacks up to a staggering 37,000 tons of wasted salad leaves, the equivalent of 178m bags each year. They’re so easy to slip in the trolley — a handy stand-by, we think. But often they’ve turned to pond weed before we get round to eating them.

For something so watery, airy and insubstantial, bags of salad are remarkably expensive. The most basic mixed bags, often bulked out with cheap iceberg lettuce and red cabbage, cost about £7.50 a kilo, which is the same price as really high-quality butter. Bags of more expensive, boutique-chic baby leaves such as pea shoots, chard and wild rocket can set you back about £23.50 a kilo, the price of 2kg of best steak mince. Rotten value, really.

Try these

It’s cheaper, fresher and healthier to buy whole, firm lettuces (1 gem, 2 frisée, 3 endive, 4 radicchio) and to break them up and wash them yourself. To preserve more of their nutritional value, break the leaves off the whole head only when needed. Invest in an inexpensive salad spinner.

Buy mixes of more tender salad leaves (5 lamb’s lettuce, 6 Japanese greens, 7 baby chard) from farm shops and market stalls that sell them just picked, not in “modified atmosphere” packs. These haven’t been technologically interfered with, so you can see if they are fresh.

Try to eat the salad the day you buy it. Or grow some cut-and-come-again leaves of your own. One small window box will give you fresh pickings over the warmer months.

The Sunday Times, 3rd September 2017