16/11/2015 4:10 PM AEDT | Updated 15/07/2016 12:51 PM AEST

Washing Fruit And Vegetables: How And Why

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UK, London, fruit and veg for sale in Borough market, Southwark.

You pick up your fresh fruit and vegetables each week from the farmers market or local supermarket and pop them in the fridge, assuming the produce has already been washed. And anyway, a little dirt never hurt anyone, right?

"While is it commonly thought that not washing fruits and veggies is no issue, and even thought to help boost immune function when we expose ourselves to soil and other "natural" substances, the truth is that even fresh fruits and vegetables can be carrying dangerous bacteria including E-coli, which is a common cause of food poisoning," Dietician Susie Burrell told The Huffington Post Australia.

Laura Ryan, Accredited Practising Dietitian, agrees. "Fruit and vegetables can be contaminated with soils, pesticides, bacteria and other pathogens which can be harmful to human health and must be washed prior to consumption to ensure safe consumption."

"Fruit and veg that aren't washed will likely contain a higher level of residue compared to fruit and veg that is washed, however there is still debate about pesticides and whether they pose a risk to our health," Ryan said.

Buying organic or growing your own fruit and vegetables is also a good way to ensure you consume pesticide free produce, however that isn't always possible.

"There is some research to show some pesticides might be carcinogenic, while others are believed to cause a range of health problems including developmental disorders, birth defects and other health problems. Food Standards Australia New Zealand (FSANZ) have strict guidelines to ensure chemical residues are always below the international standards deemed safe for consumption, however if you are concerned, it’s best to limit your exposure by always washing and/or peeling fruit and vegetables," Ryan said.

Ideally all fruit and vegetables should be washed prior to consumption, and visible soil should always be removed. However non-visible bacteria and pesticide residue may be present too, so it’s vital to wash all regardless of visible appearance.

Ryan provides this list of higher risk fruit and vegetables:

Home grown vegetables as they may have more visible dirt and contamination (for example households with pets which may contaminate soil with faeces).

  • Melons. Melons should be washed prior to cutting. Cut melons are at a higher risk of contamination from pathogens and must be refrigerated and covered after being cut to minimise the risk of pathogens growth.
  • Sprouts. These are often eaten raw and therefore do not have the benefit of many other cooked vegetables where the heat can destroy the harmful bacteria. There have been two outbreaks of Salmonella poisoning in Australia recently thought to be caused by sprouts. According to the Food Safety Information Council washing sprouts is not very effective as laboratory studies have shown that bacteria can be internalised in the sprouts, making it difficult wash off/sanitise, and bacteria can be protected in a biofilm on the sprout surface. Raw sprouts should not be eaten by vulnerable groups (pregnant women, elderly, young children etc.) And they should always be consumed within the used-by date.
  • Any fruit or vegetables to be eaten raw, as the bacteria will not be killed via the cooking process.

Fruits which are peeled prior to consumption such as bananas are safer, though as a general rule all fruit and vegetables which are to be consumed should be washed.

"As there can be contamination between the skin of the fruit or vegetable and the knife when it cuts through the flesh of a banana, avocado, pumpkin or mango, it is recommended that all fresh produce be washed," Burrell said.

As to exactly how to wash them most thoroughly, Ryan offers this advice.

"It’s best to wash all fruits and vegetables with cool running water directly before use to remove soil and bacteria from the surface of the food. Bacteria is most often in the soil attached to the produce, meaning a rinse under running water while rubbing with your hand can remove any remaining soil and minimise your risk of consuming any harmful bacteria.

It’s important to then clean your hands, boards and knives before preparing other foods, just to make sure you don’t transfer the soil to the other produce. A good tip is to not wash before storage as this might lead to your produce going mouldy, best to wash just before you are going to eat or prepare it."

For those partially concerned, several brands offer fruit and vegetable washes used to remove residual pesticides.