Can you leave dirty dishes overnight? A microbiologist weighs in

We’ve all had those moments where we can’t bear the thought of doing the dishes after dinner, especially if we don’t own a dishwasher. So the pile of dirty plates, bowls and cutlery gets left overnight until the morning when we’ve got more energy.

Unfortunately, a microbiologist warned this is doing more harm than good and risks causing plenty of problems for our kitchen that we’ll have to deal with later. 

“Kitchen sinks have germs, from contact with foods, including raw ones, and they are damp. Swab studies have consistently identified high concentrations of bacteria, such as E. coli, Enterobacter, Staphylococcus, Pseudomonas, and others in kitchen sinks,” Cindy Gunawan, Associate Professor at the Australian Institute for Microbiology and Infection, University of Technology Sydney, told nine.com.au. 

“Leaving dirty dishes overnight, in particular with food scraps still on the dishes, has risks of bacterial growth. It has risks of odours, as well as attracting pests, like cockroaches and flies.”

If you soak the dishes overnight in the sink with water, thinking that’ll help prevent odours and pests and give you a head start on washing them the next day, you should think again. Gunawan said it’s “even riskier” than leaving them stacked on their own.

“Food residues and water provide ideal breeding grounds for bacteria; along with the temperatures common in kitchens (20-25C), at these temperatures, many bacteria can double every 20 to 30 minutes,” she said.

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When you do need to soak heavily soiled dishes, such as saucepans and baking trays, one to two hours is the maximum time you should leave it for. But Gunawan warned even that is too long for “starch and protein rich residues like dairy, eggs, rice, pasta, meat”.

For those who have left their dishes overnight and are now concerned about the bacteria that has since multiplied on their dishes, rest assured the standard washing process will make them clean again by removing germs.

“Yes, hot soapy water is usually enough, if done properly with thorough scrubbing, thorough rinsing and air-dry ... washing dishes right after use is still better,” she said.

But there are some households where the nightly dishes just shouldn’t be skipped.

“While once-in-a-while lapses are usually OK for healthy individuals, there are risks of infections through open cuts on hands, even foodborne illnesses, if not cleaned properly, for people with weakened immune systems, for instance the elderly, or babies (digestion) with their still developing immune systems. There are also risks of infections with 'left overnight' utensils used to handle raw meats,” she said.

When you need to leave dirty dishes overnight, there are a couple of things you can do to make them ever so slightly less gross. 

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“Get rid of food residues from dishes and do dry-stacking. But even with this, bacteria can still survive, although the growth will be slower with minimal food residues and moisture, and it can still attract pests,” Gunawan said.

So what can you do to make washing up easier and yourself more likely to do it before bed? Washing up dishes after each meal means there is much less to do at night, especially if you are doing any cooking.

Another option is to have a dish scrubbing brush and wash things as you use them. The scrubbing brushes with handles that dispense dishwashing liquid make this even easier as you just need to run hot water and get scrubbing before putting on a rack to air dry. 

Thinking about how good you’ll feel that the dishes are done and ready for the next day is good motivation to get washing. Playing music or anything you enjoy listening to can also make the task more fun.