Heavy whipping cream is cream with a butterfat content that ranges between 36 and 40%. This term is most commonly used in the American dairy industry, with other countries having their own grades of whipping cream. For example, the closest analog in Britain is simply known as whipping cream, while British double cream has a butterfat of 48%, making it much richer.
The high butterfat content of heavy whipping cream makes it extremely rich, and allows it to develop a very full mouth-feel when it is whipped. Typically, the cream doubles in size during the whipping process, and it becomes extremely thick. It can be used to top desserts and drinks, frost cakes, and in a variety of other applications. It is also the easiest to whip, since it is so dense.
Cream with varying butterfat contents is produced by skimming the butterfat from the top of milk and running it through centrifuges to separate out its components. Butterfat is extremely heavy, so it tends to be the last thing to leave the centrifuge. As a result, the longer cream is left in a centrifuge, the higher the butterfat content will be. Because butterfat plays a critical role in how milk and cream perform in the kitchen, most countries have a clear standard to define the various types of milk and cream, ensuring that they are consistent.
In the store, you may have trouble finding heavy whipping cream. Many dairies simply use the term “whipping cream” on their package, without specifying whether it is heavy or light. As a general rule, heavy and light whipping cream behave very similarly, so it is usually safe to use generic whipping cream in a recipe. Light whipping cream, by the way, isn't “light” in the sense of calories, as it has a butterfat content between 30 and 36%. If you absolutely must have the heavy variety and you can't find it, try ordering it through a restaurant supplier.
Like other dairy products, heavy whipping cream should be kept under refrigeration to prevent it from spoiling. It should also be as cold as possible during the whipping process. Cold cream is easier to whip, and it also performs better during the whipping process, developing a smooth, dense, creamy texture. Warmer cream will churn when it is beaten, turning into butter instead of a frothy bowl of whipped cream.