In the vegetable aisle of my local supermarket I am greeted with row upon row of ready washed, ready-to-eat salads in plastic bags full of air (sort of like pillows). They all look good, the leaves are green and fresh and there is no sign of discolouration or wilting. In fact, the word 'exotic' springs to mind.

What's even better is that all I have to do is split open a bag and stick the contents on a plate, perfect for when I'm too busy to bother with sorting, washing and chopping vegetables. So I get a nice, tasty, nutritious salad with minimal effort. Or do I?

Chlorine Washes

It turns out that much of this fresh, ready-to-eat salad has more in common with my local swimming pool than a field of lush green lettuces, for it is likely (unless it is organic) to have been disinfected with chlorine (a powerful bleaching and disinfecting agent).

Chlorine washes are used to prevent disease-causing bacteria from contaminating pre-prepared salads. My first thought was that perhaps this is no big deal, after all tap water contains chlorine, so if I wash it at home I'll only be doing the same, won't I? Well, not quite.

Chlorine levels in tap water are tightly controlled and are typically restricted to no more than 0.5 mg/litre. It is common practice to use chlorine washes that contain up to 100 mg/litre of chlorine to rinse food that's sold as 'ready-to-eat', or to put it another way, 200 times as much chlorine as tap water.

Alarmed? Well don't be. UK Government legislation permits this as long as all residues that might pose a health risk are washed off. What you really need to worry about is the by-products.

When the sap from picked salad leaves reacts with chlorine, this can generate chloromines. Chloromines are known causes of eye and respiratory irritation. Unfortunately there is little or no research available to tell us if the by-products of pre-packed salads are harmful to us or not, or if indeed the people who pack them are in any danger.

Members of the Fresh Prepared Salads Producer Group have responded to concerns about chlorination by-products and ill health by carrying out their own tests, the results of which they claim show no cause for concern. I am giving them the benefit of the doubt while remembering they have an invested interest in producing such results.

Interestingly enough, EU Directive 2092/91 bans the use of chlorine for decontaminating organic food. This means that chlorine cannot be used to wash organic food anywhere in the European Union, including the UK.

Some countries, including Germany, Denmark, Holland and France do not allow chlorine washing of any fruits or vegetables; water used to wash them must not contain higher levels of chlorine than ordinary drinking water.

Modified Atmosphere Packaging

The chlorine issue aside, appearances can be deceptive, as a salad 'pillow' is not full of air as I (perhaps naively) first thought. The plumpness of the bag is down to Modified Atmosphere Packaging (MAP), a process whereby oxygen is removed from around the food in order to stop oxidation and the subsequent browning of leaves.

This is why as soon as a bag of salad processed in this way is opened it has to be used up quickly; the presence of oxygen starts to cause spoilage. In essence, by modifying the atmosphere around the food, MAP serves to increase its shelf life.

MAP can also involve the addition of other gases, namely carbon dioxide and nitrogen. This is because some disease causing bacteria are still able to survive in the absence of oxygen; the additional gases prevent them multiplying by making the atmosphere inside the bag more acidic.

It is of paramount importance that foods packaged without oxygen are stored and used exactly according to instructions (sometimes within 24 hours of opening). The absence of bacteria means there will be no odours when the food starts to spoil, and you may not be aware when it becomes unsafe to eat.

Again the Fresh Prepared Salads Producer Group says that foods prepared using the MAP process are perfectly safe, and that MAP ensures food is as fresh as possible by the time it reaches the supermarket shelf.

Furthermore, the manufacturers of ready-to-eat salads and the supermarkets they supply work together to ensure the food gets to the consumer as quickly as possible after harvesting and packing. Even so, this can take up to three days if the salad is grown in the UK, and up to seven days if it comes from Europe.

So What's My Verdict?

Whether any residues left on salad related to chlorine washing are harmless or not, drenching fresh salad leaves in chlorine does not appeal to my taste buds.

I can't help but raise an eyebrow at the fact that chlorine washing of fruit and vegetables is not permitted in some countries and banned completely on all organic food in the EU.

MAP means that no artificial preservatives are needed to keep the food fresh, so this for me is a big plus. But I'm still not sold on the idea of my 'fresh' salad leaves sitting in a sealed bag of an unnatural mix of gases for possibly days on end.

On two separate occasions I have discovered live bugs in ready-to-eat salads I have bought. This leads me to take the view that if they were still alive, the chlorine process and the gases can't be harmful. But if the washing process does not get all the bugs off what's the point in paying the extra money to have it washed for you?

So are pre-packed salads better or worse than loose, unwashed salad vegetables? For me, the jury is still out. So how do I buy my salad now I have investigated this issue? It depends how lazy I'm feeling.