Sanitising surfaces

Food safety and practical tips

3 min readOct 11, 2021


Photo by Clay Banks on Unsplash

Bleach is an effective sanitiser, as is acidifying with distilled vinegar. Add some soap to wash your hands and that is all you need — expensive cleaning products claiming to ‘kill 99.9% of household germs’ are best avoided.

A 200 ppm solution of bleach can kill microbes in about 2 minutes and is dilute enough to be left on surfaces. A stronger solution is instantaneously effective, but needs to be washed off (creating the potential for secondary contamination, for example if the surface is then dried with used linen).

Select bleach with sodium hypochlorite as the active ingredient and without additional unnecessary ingredients such as ‘lemon scent’. Check the strength on the label, usually provided as % available chlorine (not the same as the concentration of sodium hypochlorite). If in doubt, assume a 5% concentration (fairly typical). Note also that bleach deteriorates naturally with time and some manufacturers will give the residual percentage at the use-by date (it usually halves).

The quick rule to get 200 ppm is to divide the % of chlorine into 20 to get the ml of bleach to dissolve in 1 litre of water. So, for a bleach labelled with a 5% concentration, mix 20/5 = 4 ml of bleach (a scant teaspoon) in 1 litre of water (1 teaspoon = 5ml; one part per million equals one mg/litre).

For the stronger (instant) sanitising solution the simplest thing is to aim for a 1% solution, so for bleach with a 5% concentration, mix 1 part bleach with 4 parts water.

If sanitising with vinegar — use 1 part of vinegar mixed with 2 parts water. Vinegar is best for wooden boards as they can discolour with bleach.

These solutions can be stored in clearly labelled spray bottles for ease of use.

Other considerations for kitchen hygiene: the sink is a dangerous place — not recommended for washing foods (e.g. vegetables) to be served raw (use a bowl) or else clean scrupulously and sanitise before and again after washing the food. Linen towels are a great source of cross contamination, especially if they are used to wipe surfaces, dishes and hands (and are damp). Consider using recycled paper towels or disposable wipes. Sanitise linens frequently. Kitchen sponges are microbial heaven and can spread infections if used to wipe surfaces — they can be disinfected in boiling water (5 mins to be sure), soaked in beach or vinegar, or microwaved (wet and wrapped loosely in plastic).

By the way, the 5-second rule for the safety of food dropped on the floor is an urban myth — if there are microbial colonies on the floor then the food will be infected immediately on contact (microbes are in constant and relentless motion). The floor may well be safe though, for example microbes require moisture and colonies can take about 4 hours to establish themselves, whereas most people would wipe up spills and keep their floors dry (although as with knife cuts, floor scratches are an issue). It is sobering to think that the floor could be healthier than the sink (or the sponge).

And finally, if in doubt about the safety of food then throw it away — the cost of discarded spoiled food is trivial compared to the cost of illness. In Australia, annually, food-borne illness results in: 18,000 hospital admissions; 120 deaths; 2 million lost working days; 1.2 million GP visits and 300,000 prescriptions for antibiotics. There are 15,000 new cases every day.




Science of cooking, eating and health. Retired neuroscientist.