Unfortunately, there’s no straight answer – you might as well ask how long a ball of string is.
It’ll mostly depend on how often you use the oven and what kind of food you use it for – a busy canteen cooking lots of roast meats will certainly need cleaning much more often than a domestic oven in a vegetarian household.
However there are warning signs – which are even easier than having to remember a date. Here are some things to look out for, to tell you when you’re in need of a serious clean.
If you can see dirt, grime, and burned-on carbon on your oven, it needs cleaning – especially if you can see any fat. When fat is reheated it can combust, and other dirt can release noxious fumes that won’t just smell bad but change the taste of your food, and maybe even cause cancer.
Besides, if you clean your oven every time you notice grime it’ll never build up and become a three hour job to clean!
If smoke comes out when it’s on, it needs a clean. If it’s thick, black, putrid-smelling smoke it seriously needs a clean! If there’s nothing in the oven to burn but you’re still getting smoke, you can be sure that it’s burnt-on carbon producing that smoke. As above, it changes the taste of your food and can be dangerous to your health.
You Can’t Remember the Last Time
This one’s a biggy. If you have no recollection of when you last cleaned your oven, you probably should. You might think that it’s okay, given you can see no grime or smoke, but there’s more going on beneath the surface than you might think – there could be dirt you can’t see blocking up the inner workings, preventing it from reaching the right temperature and generally making it more inefficient.
Don’t wait for your oven to start producing noxious gasses before you tackle it. Remember to clean up spills as soon as you’ve made them (once the oven has cooled) and give it a good clean every now and then. Every six months is usually a good timeline, but don’t allow it to become inefficient – and make sure you don’t leave it too long, or you’ll definitely need an oven cleaner.