Well. That was an unexpectedly drawn-out blog holiday, was it not? Lovely science fans, I am so sorry the delay… it all started with a week in Cornwall. Unfortunately for my holiday, but fortunately for my career, I had to cut short my Cornish idyll to rush home for some job interviews, which I then got offered. I have spent the past fortnight finishing up freelance work, equipping myself to do a job where I don’t work in my pyjamas in my spare room, and generally giving myself a bit of a break to celebrate the end of months of rubbish job hunting. By the time you read this, it will be my first day in my new job, which is exciting. So, I apologise for the extended blog break, sometimes a girl just needs a holiday. And a new job.
Anyway, before I went away, Kat sent me a kitchen science question. She asked me “why does whipping cream make it go stiff? And does temperature have an effect on the time it takes to whip?”
I actually love this question. I love when people ask me questions for the blog anyway, and I particularly love when they ask me things I had never thought to wonder about but immediately NEED to know as soon as I get asked. In fact I read this question in the supermarket, and forced my husband to come and spend 5 minutes with me reading the labels on the various pots of cream trying to figure out the answer myself.
I figured that there must be a clue to the answer in looking at the difference types of cream, because single cream is difficult to whip into a stiff foamy solid, whereas whipping cream or double cream is considerably easier. The most obvious difference between a pot of single cream and a pot of whipping cream, apart from the different coloured packaging, obviously, is the fat content. Single cream has around 30% fat, whereas whipping cream has 36-40% fat. Double cream has 45%+ fat content. It was fairly easy to assume that this is the crucial difference that allows the change in consistency. And indeed, it is, but what’s more interesting is how it works…
Cream is basically fat-full, low-protein milk; if you leave fresh milk alone to stand then globules of fat naturally float up to the surface and bob around, creating a fatty creamy layer of deliciousness that can be skimmed off the top, leaving the majority of the protein behind. This cream, with its high fat content, can be whipped.
Whipping creates air bubbles. This is actually true in any liquid, if you whisk water it becomes bubbly, however the bubbles have no strength and are liable to pop at any moment. If you are going to create a solid mass of trapped air bubbles, you need something to keep them in place. This is where fat comes in. Fat hates water; it cannot stand to be around it. This is why fat tends to form globules in water, it arranges itself so that only a small outer region that doesn’t mind the water faces outwards, leaving the rest of the cowardly molecules to hide themselves away from the big scary water. Whipping, however, disturbs the fat. The globules are forced to whizz around the place and bash into one another. The protective membrane that shields the globules from the scary water is ripped away by all the whizzing and bashing. Fat is suddenly naked in the face of the water.
This is not something that fat molecules can cope with; once they have been forced out of their globules they will choose to arrange themselves in one of two ways. Either they will face air, or they will face each other. Arranging themselves like this forces them to form a network of fat surrounding air bubbles, trapping them in place. And there you have it, stiff fluffy whipped cream.
However, it is possible to over-whip cream, as I know only too well, because I have a tendency to assume that more force = better in the kitchen. Now that I understand the science behind why this is not at all true, perhaps I will learn, because continuing to beat the cream after the fat network has trapped the bubbles actually destabilises the network, the fat begins to be able to reform globules of pure fat, making the mixture greasier, and liable to weep. Poor sad over-beaten cream.
Finally, Kat also asked me whether temperature makes a difference on how long cream takes to whip. The short answer is… yes. Colder cream whips faster. Warmth softens the fat, weakening the framework that traps air bubbles. So if you want perfect fluffy whipped cream you need it to be cold, with a high fat content, and to know when to stop. Otherwise you’ll make your cream cry.