I just wanted to make a wonderful latte at home without an espresso machine. I don't have a great deal of space on my kitchen counter it seemed like it would be simple enough.
Yet, with a whisk in hand, and after several efforts based on instructions from the barista and internet searches, the resultant foam poured over the coffee didn't look or taste quite as I had hoped for.
I tried 2% low-fat milk and 4% full-fat milk first and the foam was - well cold foam not frothy and rich.
Then I tried heating the milk before frothing with no better result and then making the whole drink and putting the finished drink in the microwave to heat. Still not good at all.
Trained as a food scientist, I thought now I need to use my knowledge to solve this dilemma. My mind recalled an interview I had at a leading food manufacturer. I was asked only one question - tell me everything you know about milk.
Actually, there is quite a lot to know about milk, and yes, I was offered the job. But to be brief for this purpose I'll share only the pertinent highlights you need to know to create my perfect froth at home with or without fancy equipment.
Milk contains the three major macronutrients - about 4% each for this example: 1) protein (casein or curds when heated and whey), 2) carbohydrates (lactose which is milk sugar - the lactose intolerant are far too aware of this) and, 3) fat, of which roughly 65% is saturated (solid at room temperature). The remainder of the milk is simply water - 88%.
All three macronutrients contribute to my perfect froth.
The process of creating the froth I love works best with whole milk containing the most fat and therefore the most saturated fat, the component of milk fat that is most solid at room temperature. The colder the milk the more solid the fat is. I am using homogenized milk which means the components of the milk are mixed under pressure to make smaller fat particles which help to strengthen the natural emulsion of the milk improving mouthfeel, taste and, shelflife of the milk. Most of us know that fat/oil and water do not naturally mix. That is where the protein casein comes in because it is a natural emulsifier.
We start with cold milk when making froth because it is easier to whip air into a solid structure. We are trying to incorporate fine air bubbles into the milk and develop a stable structure to support the froth. The process of steaming while whisking results in vaporized air and water above the surface of the liquid incorporating air into the milk.
To maintain the structure's stability, the protein in the milk needs to be heated slowly so that the casein protein component can separate from the whey protein component. The casein will coagulate as it is mixed with the milk fat while being aerated and heated. Froth containing the aerated saturated fat structure creates a more stable foam with a rich mouthfeel.
The other key component for success is to note that the milk is whisked while it's being gradually heated to approximately 70 degrees. We want the foam to be warm, not only for enjoyment but also because the foam and the coffee that we drink at approximately 175 degrees are closer in temperature when combined. This is important because when the froth-containing fat in the foam hits the coffee the fat doesn't immediately turn to liquid fat due to the temperature differential and rather melts on your tongue at approximately 98.6 degrees - body temperature as the warmer coffee and the foam combine in your mouth.
I am thrilled with the outcome of my froth and look forward to my morning lattes now. But why stop there? I enjoyed hot chocolate drinks with high-quality cocoa in the evenings over the holidays and with egg nog (eggs are high in protein and froth well with milk). I sprinkled a coffee latte with cinnamon or added a splash of schnapps or other alcohol as an after-dinner drink.
If you don't want to use whole milk for one of many dietary reasons, based on individual preferences for taste, health, personal values, and/or lifestyle and you want to adapt your frothing method for ingredients you love, let me know in the comments below.
Or contact me at mindy@foodfitter.com for more help to solve any sourcing, shopping, and kitchen challenges based on the science of food. Let's have fun with food, entertain yourself and others with new skills, and become more comfortable creating food that you design.
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