Milk’s sexy cousin has some surprising chemistry.

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Even an average cook like me knows that if you want to make something taste better just add cream or butter. Or both.

When it comes to cream, if this was all it did, it would be enough. But it isn’t. Without cream desserts would be a whole lot less interesting. Whipped, clotted, flavoured or even just poured cream makes some desserts worth eating.

Let’s face it. No one would eat a scone if it didn’t come with cream. They’re too dry. For me, a scone’s only purpose is to get cream into my mouth.

It’s hard to credit that all the luxuriousness of cream comes down to something as as mundane as chemistry, but it does.

It’s what us scientists keep saying. Chemistry can be sexy too.

What is Cream?

Most of us know that you get cream from milk. I’ve already covered milk so we know that milk is an emulsion where milk fats are packaged into globules called, somewhat unimaginatively, milk fat globules.

Cream is just milk with a lot more fat globules and lot less water.

Almost all the chemistry behind the luxurious mouth feel of cream, it’s ability to be whipped into structured foams and its ability to enrich sauces stems from the fact that cream has a stack of fat packaged into little globules floating in water.

How the Creaming Process Works

Mostly, we’re all used to our pasteurised and homogenised milk that we buy at the supermarket.

But if you take raw milk and let it sit, cream naturally forms as a layer at the top of the milk.

This process, called creaming, occurs because the fat globules are less dense than water. So, over the course of 12-48 hours, they float to the top of the milk and form the layer of cream.

For most of human history skimming cream manually from milk was the only real way to make cream.

In those days the cream was gathered from pooled milkings that were a day or two old. Because it was sitting around for so long the cream also had a bit of fermentation going on which provide a different taste.

These days cream is made using fresh pasteurised milk in centrifuges. This not only speeds up the creaming process but it is also much more efficient with most of the dairy fat globules being purified from the milk.

Cream Fat Percentages Compared

Modern cream production also provides a measure of control. Manufacturers can produce creams with a well defined proportion of fat.

In the supermarket we can select a creams with different amounts of milk fat globules: lite, whipping, double and heavy creams, for example.

Annoyingly, these creams can have different names in different places. So, when following a recipe, it’s a good idea to understand how the cream is being used in the dish, rather than relying on the name of the cream.

Cream Variety	Min. Fat Content	Primary Culinary Use	Science Behind Behavior
Half-and-Half / Light	10% – 18%	Coffee, light soups	High water content; will curdle if boiled with acids.
Single / Whipping Cream	30% – 36%	Sauces, light whipping	Minimum threshold needed to trap air bubbles into a foam.
Heavy / Double Cream	36% – 48%	Stable whipped cream, rich sauces	High fat globule concentration resists curdling at high heat.
Clotted Cream	55% – 60%	Desserts, scones	Indirect heat evaporates water, concentrating fat globules.
Crème Fraîche / Sour Cream	18% – 40%	Dips, garnishes, baking	Bacterial cultures turn lactose into lactic acid, thickening proteins.

Mostly, cream’s behaviour comes down to its fat content. If you know what you are using the cream for you can normally pick which one to get based on it’s fat percentage.

Thickened cream

Some creams have added thickeners like gelatin. In Australia we have ‘thickened cream’, that is a thicker cream for ‘dolloping’ and which can be easier to whip. There is nothing you can’t do with a pure cream that you can do with a thickened cream so I usually stick to pure cream.

Culinary Chemistry: Cooking with Cream Without Curdling

If you can resist just drinking it from the bottle, cream has a lot of uses in the kitchen. One of the most common uses for cream is to add some luxuriousness and ‘mouth-feel’ to to a sauce, soup, curry or stew.

Because cream is full of fat it slightly thickens and improves the texture of liquids while providing fatty flavours that increase the richness of the dish.

Cream can be used this way, adding it to hot or potentially acidic foods, or even deglazing a hot pan, because it won’t curdle like milk. If a cream has a high enough fat content, about 25% according to Harold McGee, it can handle conditions that would curdle milk.

We already know that milk curdles because caseins denature and clump together to form curds when exposed to acidity or high heat.

Not only does cream have less caseins, it is also stabilised in adverse conditions by the ability of the fat globules to interact with caseins molecules as they begin to denature.

That is not to say that cream won’t curdle. It can curdle but a simple rule of thumb is that the heavier the cream the less likely it is to curdle.

The Science of Whipped Cream: From Liquid to Foam

You can add both lightness and structure to cream by whipping it into a foam. Anyone who likes dessert is familiar with this use of cream.

Once again it’s the fat content of a cream that determines how much structure you can get out of the cream.

Whipped light cream forms a less dense foam for dolloping while a whipped heavy cream forms a denser foam that can form layers in a cake or be piped to form long lasting decorations (sometimes with the help of stabilisers).

Whether lightly or strongly whipped, whipped cream is a foam, a stabilised network of air bubbles dispersed throughout a liquid. And the magic behind cream’s ability to become a foam comes down to what happens to milk fat globules when cream is agitated.

Building Structure in Cream

When we first attack some cream with a whisk we are repeatedly forcing air through the mixture.

Initially this air bubbles out of the cream as there isn’t enough surface tension to trap the air and it can just slide out between the fat globules and water molecules.

But as you keep whisking the fat globules are bashed together and begin to lose parts of their phospholipid membrane exposing patches of fat.

We know that fats are hydrophilic and don’t like interacting with water so they will either stick to another globule’s exposed fat patch or align to face an air bubble.

Over time you will start producing a network of globules bound together by their fat patches, a network that will eventually provide enough surface tension to start trapping the air bubbles.

The more you develop this network the more air bubbles you’ll trap and the more structure you’ll have in your whipped cream. From this it stands to reason that you need a certain amount of globules to build the network. A rule of thumb is that you need at least a 30% fat cream to easily make whipped cream. It also follows that the higher the fat content the stiffer you can make the foam.

But be warned. If you go too far you’ll damage the globules too much and start liberating free fats that will coagulate. When that happens you’re on your way to making butter.

This is why over-whipped cream is grainy, you’ve got bits of butter in it.

Temperature Effects on Fat Globule Aggregation

Another important consideration when whipping cream is temperature.

When whipping cream you are building structure using fats as your building material but fats like to melt.

So, you want to start cold, 5-10$\degree$C, and you want to keep it cold because any melted fat will affect the structure of your whipped cream.

A lot of sources recommend chilling the mixing bowl which probably isn’t a bad idea as whisking itself causes a temperature rise, though if you are using an electric mixer you might be quick enough. Depends how lucky you are feeling.

You also want cream that has been chilled for a prolonged period of time, what is called ‘ageing’ your cream. This promotes the formation of some butterfat crystals that will help remove the fat globules outer layer speeding up the whole process.

You Can Also Add Some Acid

You can also make it easier to whip cream by adding acid.

Acid denatures the proteins on the surface of the milk fat globules again making it easier to disrupt the out layer and expose the fat.

Be careful though, too much acidity will affect the taste and weaken the structure of your whipped cream. Harold McGee recommends 5 ml lemon juice per 250 ml of cream, which seems a good place to start experimenting.

The Flavour Of Cream

Cream by itself, straight or whipped, has a fairly neutral flavour. The most noticeable aromas being caused by common chemical building blocks called lactones (in chemistry-speak cyclic carboxylic esters).

Lactones also cause the “fatty” aromas that are present in peaches, coconuts and barrel-aged beers (I can imagine cream with peaches or coconut but beer? I’m not so sure).

This neutrality makes cream perfect for something like strawberries and cream where it brings a richness and mouth feel while leaving the flavour to the fruits.

Because of creams neutral flavour, though, it probably didn’t take long before humans were tarting up whipped creamed with sugar or other flavours.

Today, the most well-known sweetened whipped cream is Chantilly cream, a whipped cream that includes vanilla flavouring and castor sugar. The French, of course, claim it was invented in the French town of Chantilly in the 17th century but it is likely to have been an Italian invention.

Clotted Cream

A 16th century English form of cream, but one that has survived to the present day is clotted cream. Though less known outside of England clotted cream is still popular in it’s home country and is served on scones or fruit.

Essentially it is super-high fat content cream that is produced by heating milk almost to a boil for several hours and then letting it cool before skimming off the cream.

The boiling gets rid of some of the water, hastens the rise of the milk fat globules and melts some of the fat to create butter fat.

In England, by law, it needs to be at least 55% fat, though typically it’s around 65% fat, so not something you want to eat by the tub full.

Although typically associated with England (Devon in particular) it is also has a cousin in Turkey, where it is called kaymak, and there is a Persian version called sarshir.

Fermented Creams

Finally we come to our fermented creams. As I mentioned above, in medieval times the cream had probably already undergone some fermentation.

In the absence of modern technology our ancestors had to wait for the cream to rise to the surface and during this time lactic acid fermentation would have occurred.

Because we are able to separate our cream a lot more efficiently the cream we buy will not have had the time for any fermentation. The milk is also typically pasteurised before creaming, so to achieve products like sour cream or creme fraiche manufacturers need to add bacteria to ferment the cream.

Creme fraiche and sour cream are quite similar and are both produced commercially by inoculating cream with lactic acid bacteria and fermenting.

The main difference between the two is that creme fraiche has a higher fat content and is thicker than sour cream which has a lower fat content and is thinner but more acidic and and ‘tangy’.

In general, because of the fat content creme fraiche has a greater resistance to splitting than the lower fat sour cream so if your going to simmer for a while use creme fraiche.

If using sour cream, which you might want to do because of the acid it will bring to your dish, add it late in the process. If you want to make them at home there are some simple recipes here.

Conclusion

It turns out that there is a lot more to cream than one would initially think. Who’d have thought a bunch of fat floating in water be so useful or have such complex chemistry.

As I alluded to above, whipped cream is a way-point on our way to butter. You can think of butter as what you get when you over-whip cream, but that is a topic for another post.

For now we can be thankful that we have cream, without which scones would be useless things good for no one.