When gasses like oxygen (H₂O) or nitrous oxide (N₂O) are injected into milk or cream foams of different textures are created. Dairy foams happen because whey and casein in the milk protein becomes denatured forming a thin film that traps the gas and creates bubbles. Foams may be light and airy bubbles, frothy or dense, or thick like an espuma. Whether you are creating hot varieties accompanying coffee drinks or cold dessert creams, temperature and fat content are critical factors in creating foams.
Heavy cream with 30-40% butterfat forms a stable cold foam because the fat surrounds the denatured proteins and holds the air in place. But whipped cream will easily fall if it gets too warm. Stabilizers, including lecithin, agar, gelatin, and xanthan gum can be added to foams to create greater volume and steadiness.
Foams made with milk are less stable than cream and don't hold up as well unless combined with stabilizers. Fat free (skim) milk creates better bubbles than whole milk at 3-4%. That's because in fat free milk the proteins do all of the work and in whole milk the small amount of fat works against bubble creation. Skim milk foams the best at 110°F/ 45°C, but as the heat is increased the fat content in whole milk helps it create a similar volume.
Foams are aerated through the use of a whisk, either by hand, in a mixer, or with an immersion blender. Cream can also be foamed with a nitrous oxide (N₂O) charger, called a thermal whip or a whipping siphon. Cream doubles in volume when whipped by hand or with a mixer, but will increase by about four times its volume if it is foamed with a gas.
Conventional Whipped Cream
It’s important to keep the cream and the utensils (bowl and whisk) as cold as possible, below 40°F/4°C, when aerating it. A balloon whisk will achieve the most volume. Sugar stabilizes the cream but prevents the cream from achieving full volume, so add it towards the end of the process as it begins to hold soft peaks. Flavor with vanilla, cocoa powder, or other flavorings as desired. Some weeping may occur if it is whipped in advance and stabilizers such as gelatin (1 tsp. gelatin melted in 2 tsp. water per cup of cream), or dried milk powder (2 tsp. per 1 cup of cream) may be added to the whipped cream. Cream that is slightly over-whipped and beginning to looks grainy can be brought back by adding a touch of un-whipped cream. If the cream has been whipped to the point of butter it cannot be brought back.
- Chill the bowl and whisk in a cooler or freezer before beginning the process
- Add the cream to the bowl and begin to whisk
- Add milk powder at this stage if using to stabilize the cream
If using a machine begin slowly until it starts to thicken and then increase the speed to medium. If whipping by hand it should take 3-5 minutes of vigorous whipping. Monitor it carefully especially if using a machine to avoid over-whipping the cream
- Whip to a soft peak
- Add sugar if desired
- Add a little melted gelatin to stabilize if desired
Foaming Cream with a Charger
Cream can also be foamed using a nitrous oxide charger.
- Add the cream to the charger
- Fit a tip onto the the cover of the charger and tighten it to the tank
- Charge the the tank with a cartridge
- Shake the charger a few times
- Invert and squeeze the handle