At Intermix Beverage and at countless coffee shops across the country, particular attention is paid to the quality and flavor of the coffee that goes into our lattes, cappuccinos and other espresso drinks. But the milk in espresso based drinks is an equally vital component.
How you steam and froth milk can be just as important as making sure you grind and tamp your coffee correctly. And understanding the chemistry behind steaming and frothing will help you make the best tasting espresso drinks in town.
Milk’s Three Magic Ingredients:
There are three solids suspended in milk that directly affect its flavor and froth-ability (so to speak):
- Lactose (or milk sugar)
- Fat
- Protein
Lactose is less soluble at cooler temperatures (that is, its ability to completely dissolve in a liquid is slowed), and thus milk is relatively unsweet when it’s cold. When milk is heated, lactose becomes more soluble and dissolves, making it taste sweeter.
As for fat content, you can probably guess that skim milk contains no fat, while 2% milk contains 2% fat and whole milk contains 4% fat. The more fat, the richer and creamier the taste. The percentage of fat also affects the stability and volume of milk when you froth it.
Froth made from whole milk is more stable than skim milk, but the volume of the froth will be less. The opposite is true for skim: you will get thinner, less stable froth but your volume will increase. If you want the best of both worlds, milk that contains over 5% fat creates both thick, stable froth and large volumes of it.
Breve, anyone?
Proteins in milk include whey and caseins. Both help create the froth. The structure of froth depends upon the structures of these proteins. These proteins work differently, but when heated, they react the same. Both of these proteins are stable at approximately 140 degrees. After that, they become susceptible to denaturing. Denaturing changes the shape and charge of the proteins causing them to react differently than they normally would.
Warning: You will not get the same quality of milk when you steam it a second time. Our best advice is to train your staff to steam only the amount of milk they need for the drink they are making. Because constantly throwing away milk can become expensive, we understand that it is not always practical to discard already steamed milk. If you do decide to re-steam milk, you should only re-steam one time only.
For now, check out this simple but quite helpful tutorial on steaming milk. It includes great use of graphics to help you gauge your technique!