Kitchen wisdom
When it comes to cake tins, size matters, so it’s time to talk arithmatic QUESTION OF THE WEEK
QIs there a formula that can help me when I am adjusting cake sizes? As there are just two of us at home and with no visitors allowed under current restrictions, I don’t want to find myself making a cake for 12. But while I can often halve or quarter the ingredients, I don’t know what size tin to use or how long to cook it at what temperature. Help, please!
LK via email
ASize does matter, as those of us brought up on baking with Delia know. It’s important to get that cake tin right. But with smaller households and no friends dropping around for a slice and a cuppa, this is a problem lots of us are grappling with right now.
Working it out is like going back to Year 7 maths class. Assuming your cake is round, I start by calculating the base area using the old-school formula: the
Here’s my handy guide to reducing cake tin sizes area of a circle = Y r2, or 3.142 x the radius x the radius.
As it’s kitchen arithmetic, we can approximate and make Y (pi) equal to 3, rather than 3.142. So a 20cm cake tin has a radius of 10cm and a base area of 3 x 10cm x 10cm or roughly 300cm2.
Still awake at the back there? Then I divide that area into half, a third or a quarter – depending how much I’m reducing the quantities of ingredients.
It’s governed by how many eggs are in the mix, as dividing eggs is a pain, so I try to keep to whole egg amounts.
So if I’m halving the quantities of a cake that uses a 20cm tin, with a base area of 300cm2, I’m looking for a tin with a base area of 150cm2. To find the diameter of the new cake tin, I have to work backwards and use the formula (new area ÷ Y) = radius – which for a 150cm2 gives me a radius of about 7cm, making a 14cm diameter tin. It’s pretty much impossible to find a 14cm tin, so I suggest using a 15cm tin.
I’m assuming most of you have zoned out of the maths by now (there’s quite enough homeschooling going on already) so here’s a chart I made (left).
When it comes to tin size, give or take 0.5cm is fine. The best ranges of smaller round tins are at thevanillavalley.co.uk or squires-shop.com. For square cakes, I’m devoted to my Silverwood adjustable cake tin which makes square or oblong cakes in 2.5cm increments up to a 30cm square. It’s currently out of stock, but the Silverwood team tell me they will have more this week at silverwood-bakeware.com.
In terms of timings, that is less hard and fast. After the first 15 minutes (for cakes under 18cm) or 20 minutes (for cakes over 18cm), start checking with a skewer, plunging it into the centre and seeing if it comes out dry. Or use a digital probe (and yes, I know our prizes are sponsored by Thermapen, but it would be negligent of me not to point this out). For a cake to be properly baked, it needs to reach the correct internal temperature, which for most cakes is 98C. The main exception is chocolate brownies, where around 82C is right, or even 10 degrees less if you like them really gooey – and who doesn’t?