|Choosen the specific milk for frothing can be quite a challenge|
I have the opinion that any Barista or Home-enthusiast most know in specific what groceries they are handling, for example to produce velvety micro foam. Therefore lets get the basics set by clearing out the different content, that milk is combined off - in other words lets get to know milk a little bit better.
In the pursuit of steaming professional micro foam there must be three thing in the milk, that we should have great focus on; fat, protein and milk sugar (lactose). Therefore we can trace this back all the way to which cow the milk is coming from? whats its mostly eating? How all it is? These among others will potentially influence the flavor within the milk and therefore also the final result off your micro foam - but don't go running around blaming the cow because you aren't producing optimal micro foam.
When you are tasting the milk or your final cappuccino result - the slightly sweetness and pleasant taste you will experience in the milk is primarily due to the relationship of lactose and chloride contents. Therefore it gives great meaning that lactose is the milk sugar - like mentioned above. The lactose - when steaming the milk and thereby also heating the milk - will begin to dissolve and in turn increase the perceived sweetness, which is what we truly want.
Milk is solid based in the quality of fat it contains and can range from 0,1% in non-fat to approximately 3,5% in whole milk. Lactose described above gives the milk a lot of sweetness and the fats doesn't provide any taste to the milk, but instead gives body to the flavor - a fuller flavor. Therefore can fat play a big part when tasting the steamed milk, regarding the mouthfeel and texture. The milk fat is therefore providing some get richness to the milk based beverage, that cannot be denied.
The most important when seeking the ultimate steamed milk is the proteins within the milk, because they are responsible for our milk being able to be foamed. Understanding how proteins play a part in this matter can be a little tricky or quite a challenge, therefore the following quote.
"Foam foramtion is mainly based on the effect that in the boundary layers of the phases, liquid and air molecules are enriched due to a boundary layer activity and therefore stabilize the boundary layers." Quote Spreer & Dekker
When you are steaming milk you are incorporating air into the milk, the proteins are hereby important because they are being absorbed by a thin film surrounding an air bobble giving stability to the entrapped air. If you are way off track here, maybe read this previous written article; Variables when frothing milk.
When you get the above - you will understand that we want proteins in our milk - but there are actually two types of foam caused by either proteins or phospholipid-protein, so does this matter? Well the relationship of fat and protein can impact how easily the milk will foam and at what temperatures milk is most receptive to incorporate air, so yes. But its an extreme technical point of view when trying to steam milk on home bases, so I will leave it as a cliffhanger.
Non-fat milk is more receivable of incorporating air at low temperatures, this applies also to whole milk although to a lesser extent. Therefore will the milk from fridge temperature and to approximately 38 degrees (100 Fahrenheit), things are looking great for the optimum steamed milk. Nonetheless from 38-72 degrees (100-160 Fahrenheit) the chemical process is reversed with the higher fat dairy products consistently exhibiting a greater volume of foam being produced at any given point.
Most importantly does temperature trumps the influence of the fat on foaming - because all milk regardless of fat content, creates the greatest volume of foam at cooler temperatures.