Why oven temperature matters
Do you blame yourself when your sponge cake fails to rise or you burn your biscuits? It might not be you.
We've tested hundreds of ovens, and found that many don't stick to the temperature you set them at. Some have even veered more than 40°C above the set temperature.
Read on to find out how oven temperature affects cooking and see the consequences of baking at the wrong temperature.
How oven temperature affects your cooking
We made a classic Victoria sponge to test how much difference an oven with flaky temperature controls will make to your cooking. Using exactly the same recipe, we baked four cakes at different temperatures, ranging from 20°C under the recommended temperature to 40°C too hot.
As our results show, even a 20°C difference can have a marked effect on the appearance and texture of your cake. And the same applies to other dishes – you may find your dinner isn't ready when you expected or that it's burnt and bubbled over before the timer goes off.
Too cool (140°C)
The cake is too light in colour, sunken in the centre and not completely baked in the middle. The structure is very compact as few air bubbles developed in the baking process.
About right (160°C)
The cake has a good pale to mid-brown colour. After cooling it is fairly flat and has a good soft structure throughout. There are some small air bubbles and few medium-sized ones. A few cracks appear on the surface towards the end of the baking process.
A little too warm (180°C)
This cake turned out slightly too dark and, after cooling, was higher in middle than at edges. There are a fair number of surface cracks at the centre from where the cake has risen then sunk back down during cooling. The structure of this cake isn't too bad – soft in the centre but slightly harder near base.
Too hot (200°C)
The surface colour is too dark and the cake is burnt around the edges. Its rise is uneven – much greater in the centre – and there are lots of surface cracks. The middle of the cake is soft textured but the base and edges are much harder.
*We used a fan oven where the recommended temperature for the Victoria sponge recipe was 160°C.
What’s happening inside your oven?
At the right temperature your cake mix should turn into a light, airy and hopefully tasty sponge that’s evenly risen, cooked through, and gently browned on the surface. This is because the reactions that occur in response to the oven’s heat – such as the fat melting, the sugar dissolving, the formation of those nice airy bubbles and caramelisation on the surface – happen in the right order and for the right length of time.
But if you unwittingly cook in an overheated oven, the stronger heat will cause moisture to evaporate too rapidly from the cake’s surface, resulting in an overbrowned cake that may be burnt on the edges before the insides are done. The overheating also affects the structure: you’ll get drier, harder sponge around the sides than in the middle.
Cooking at a too-low temperature slows the reactions down, so each stage takes longer. And although you don’t risk burning the outside, the structure of the cake can be adversely affected. The rise is less, so you end up with a denser, less airy sponge.
How common are inaccurate ovens?
Today's ovens have all sorts of hi-tech features to tempt you, including steam cooking and self-cleaning, and some can even be controlled remotely by an app on your phone. But unfortunately, this doesn't mean they get the basics right. In our most recent 2018 tests, we came across an oven that soared to 220°C when we had set it to 180°C.
While it's more common for an oven to overshoot the temperature you set it at, we do come across models that struggle to get up to the right temperature. One of our recently tested ovens was set for 180°C, but we measured the temperature in part of the oven to be just 150°C.
You can adapt to an oven if it averages just a handful of degrees away from the correct temperature by turning it up or down a little. But if it's a larger gap – or the temperature fluctuates a lot during cooking – you could be in for some disappointing results.
And it's not just built-in ovens you need to worry about. We've also found cookers which have ovens that struggle to maintain the right temperature. So it's worth checking our or before you buy to ensure you get a model that cooks to perfection.
Oven thermometers: do you need one?
All ovens have an in-built thermometer but, as explained above, some can have problems reflecting the correct temperature. This isn't great if you're trying to finish that perfect bake.
You can position the thermometer in different areas of your oven to test the temperature and find hot/cold spots. Just make sure you leave the thermometer in each area for at least ten minutes before checking for changes.
Oven temperature conversion
Use the table below as a guide when converting oven temperatures between gas, celsius, fahrenheit, and fan ovens.
Why are fan oven temperatures lower?
Fan oven cooking temperatures are typically reduced by around 20°C compared to conventional ovens. This is because the fan circulates hot air around the inside of the oven and the food, ensuring a more even temperature and cooking food much more quickly.
Not adjusting the temperature to account for this effect can cause the outside of your food to cook too quickly, so it's always worth checking the recipe.
As most ovens are fan ovens these days, you can usually assume that a recipe that only suggests one oven temperature is referring to fan ovens. Some will offer two though – a hotter temperature for traditional ovens and a cooler one for fans.
How to make your bakes great
There are many variables that can potentially affect the outcome of your bakes, from the ingredients you use to the temperature and humidity of your kitchen. Some things you can't control, but using an oven that accurately maintains the right temperature is a great starting point. Here are a few tips to stack the odds in your favour for results worthy of the Great British Bake Off.
Don’t open the oven door – This can spell disaster for sensitive dishes such as soufflés, and delicate sponges don’t appreciate it either. Our reviews highlight which ovens have great visibility through the door, so you can keep an eye on your bakes without compromising their rise.
Don’t overfill the oven – While some ovens are better than others at spreading heat evenly and supplying your food with enough heat, this is a greater challenge if the oven is overloaded. Generally speaking, cooking on any more than two levels risks poorer results.
Measure ingredients carefully – While it can be tempting to guess quantities if you're in a hurry, this is risky. The ratios for butter, sugar and flour are best stuck to in order to maximise your chances of good baking results.
Use foil to avoid overbrowning – If you notice that your cakes or pastries are browning before they are cooked in the middle, loosely covering with silver foil may save the day. This lets the warm air circulate but protects the surface from more fierce direct heat.