How to wash fruit and vegetables: contamination and food safety at home

Where does contamination of fruit and vegetables come from?

A lot of it starts in the field. Soil, untreated manure, animals and irrigation water can carry bacteria, viruses or parasites onto the surface of plants.

The FAO, the UN agency for food and agriculture, and the WHO point to two main risks during growing: water of highly variable quality and manure used as fertiliser without treatment [3]. That is why they call for good hygiene practices from the outset [3].

Next comes handling: harvesting, transport, the supermarket shelf and, finally, your kitchen. Unwashed hands or a chopping board you have just used for raw chicken can transfer microorganisms from one food to another. This is cross-contamination, and it is the part you can control.

What infections can be transmitted by raw fruit and vegetables?

The three bacteria most closely monitored are Salmonella, Shiga toxin-producing Escherichia coli and Listeria monocytogenes. According to the WHO, Listeria can reach vegetables from soil or manure. Outbreaks have been linked to prepared salads, bean sprouts, and fresh fruit and vegetables [4]. Some viruses and parasites can also be transmitted this way [3].

In a healthy person, the most common outcome is gastroenteritis that clears up within a few days. Shiga toxin-producing E. coli can lead to haemolytic uraemic syndrome, a serious condition affecting the blood and kidneys. It occurs mainly in young children and older people [5]. Listeria, on the other hand, is particularly concerning during pregnancy and when the immune system is weakened. See “Cheese in pregnancy”.

How should you wash fruit and vegetables?

Use cold, running tap water and rub with your hands or a brush. The order and technique make the difference.

1. Wash just before eating or cooking, not as soon as you get home from shopping. Storing produce while wet encourages mould.
2. Separate the leaves of lettuce, endive or spinach and wash them one by one. Discard the outer leaves.
3. Scrub hard-skinned produce with a clean brush, such as melons, watermelon, cucumber, courgette, potatoes or carrots.
4. Drain well before dressing or storing any leftovers.

Do not use soap or washing-up liquid: they are not made for food and may leave residues on the skin.

Do you need to wash fruit that you peel?

Yes, and do it before peeling. A knife or your fingers can carry anything on the skin into the flesh. This applies to melons and watermelon, which are cut with the rind on, as well as oranges and avocados. Running water and a little rubbing are enough; don’t use bleach.

Do you need to wash fruit and vegetables with bleach?

Not all of them. Bleach suitable for food use is reserved for produce eaten raw and unpeeled: whole fruit you bite into, salad leaves, cucumber with the skin on or strawberries. For these, the Spanish Agency for Food Safety and Nutrition (AESAN) recommends soaking in water with bleach, in addition to washing [1]. Produce you are going to cook does not need it, because heat does the job.

To do this properly, check three things [1].

• The label. It must state that the bleach is suitable for disinfecting drinking water; household cleaning bleach is not suitable.
• The amount. Use 4.5 ml per 3 litres of drinking water (one dessert spoon), and leave the produce submerged for 5 minutes.
• Rinsing. Rinse thoroughly afterwards under running water.

Disinfecting the surface reduces the risk, but does not eliminate it. Washing your hands and keeping raw and cooked foods separate still matter just as much.

Are sprouts and germinated seeds safe?

They’re a special case. Sprouts such as soya, alfalfa, radish or broccoli are grown in warm, moist conditions—the same conditions in which bacteria multiply.

A FAO and WHO report on sprouts adds two facts that affect how they should be handled [6]. In the outbreaks investigated, the most likely source of contamination was the seed itself. And there is currently no treatment that guarantees bacteria-free seeds [6].

Because sprouts are eaten raw or only lightly cooked, no step removes any contamination they may carry. Washing them is sensible, but it will not remove microorganisms that may be inside the seed. Buy them refrigerated, follow the use-by date and keep them in the fridge. Growing them at home carries the same risk.

If you’re pregnant or have a weakened immune system

According to the WHO, pregnant women, older people and those with weakened immune systems are at greatest risk of listeriosis [4]. Toxoplasmosis is also a consideration during pregnancy. If you’re not sure whether you’re immune, follow the prevention advice. Wash any fruit and vegetables you eat raw thoroughly. Our guide to what not to eat during pregnancy explains what to avoid and what you can eat.

If your immune system is weakened because of chemotherapy, a transplant, an illness or immunosuppressant medication, careful washing becomes part of looking after yourself. Wash anything you eat raw with extra care. Always cook sprouts, and avoid salads from deli counters. Your healthcare team may give you stricter advice for your situation; follow their guidance.

Does washing fruit and vegetables so thoroughly remove anything good?

No. Washing removes soil, dirt and some microorganisms from the surface. The fibre and the substances that feed your gut bacteria remain. Washing thoroughly lets you enjoy more raw fruit and vegetables with confidence. This variety is one of the foundations for looking after your gut microbiota.

What mistakes do we often see in consultations?

These are things we hear almost every week in consultations, and none of them is an unusual oversight.

• Assuming organic fruit or home-grown produce is clean. Soil, irrigation water and fertiliser can all be sources, whatever the growing method [3].
• Adding vinegar or bicarbonate of soda to water and assuming the vegetables are disinfected. For produce eaten raw with the skin on, the recommendation is suitable bleach, used at the correct dose and followed by rinsing [1].
• Eating less salad and raw fruit out of fear. Thorough washing lets you eat raw produce with peace of mind almost always, and variety counts for your health.
• Washing bagged salad that is already ready to eat. If the packaging says “washed and ready to eat”, washing it again in a kitchen with a recently used chopping board may contaminate it further.