What makes milk froth?

Mother’s Day started with the delightful tradition of breakfast in bed. HT delivered Latte, Toast and Honey and the first season Jonquils surrounded by Lavender as I read the latest Henning Mankell novel.

HT

HT (heartthrob) keen to impress

With all this talk of the pros and cons of permeate and its apparent effect on the ability of milk to froth I have noticed with interest the day to day frothing ability of my milk lately. My milk is as fresh as it gets coming straight from the cows to my fridge via the milk vat which drops it (with the help of the plate cooler) from 37 degrees C to 4 degrees C in the blink of an eyelid

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Now as I explained in an earlier post permeate is the option used by the big processors to ensure a consistent standard of the fat and protein content of milk for your table.

Seasonaility of Milk

This chart shows the seasonality of milk production in Australia in the years 2001 to 2002 compared to 2010/11 and as you can see the curve is getting flatter. I will explain in a later post why this is. In this case you will note Australian dairy farms produce a lot more milk in Sept to Dec(Spring). This reflects the period when grass is at its best ( high quality as well as quantity).  Traditionally this means milk protein and milk fat are lower in spring when milk volumes are higher.

Adding to the standardisation complications for milk processors Australian dairy farms systems are very diverse and what you feed your cows can have a significant impact on the milk components.

Interestingly enough as you can see from the chart below only 5% of Australian dairy farmers feed their cows on pasture alone. We fall into the “other” group in that we have what is know as a  “high input” system. To complicate matters even further our two farms have very different high input systems which results in very different fat and protein ratios in the cow’s milk on the two farms.

Production Systems

This chart describes the range of production systems operating across Australian dairy farms & how farmers are increasingly becoming more flexible and opportunistic.

Now my barista skills are good enough to impress most guests as long as I keep the options to short black, long black, latte and cappuccino but in the last month the consistency of the frothing ability of our milk has left a lot to be desired.

On the home farm we milk the “fresh” cows. That is the cows that have just calved to cows that have been milking 150 days. These cows produce less fat and protein than the cows on the Lemon Grove Research Farm who have been milking for 150 days or more. We live on the home farm so we drink the “fresh” cows milk.

Now HT likes copious amounts of cream in his milk on his weetbix and allbran so he brings home a fresh jug every morning and pours the cream off the top. (Yes his cholesterol is not good). This sometimes means we can have 3 jugs of milk in our fridge and this has allowed me to experiment with milk from different days. This morning when I had my second cup of coffee the milk wouldn’t froth at all so I sat it aside and got another jug out and it frothed up beautifully.

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Milk from two different jugs in my fridge from the same cows on different days from pasture in different paddocks

We keep records of every paddock the cows go into, what day and what time, the daily fat and protein content and the total milk, how much concentrates (grains etc.) they get in the dairy as well as the weather conditions. All well and good but as I didn’t keep records of when the jugs of milk arrived in my fridge that wont help me to come up with a hypothesis I can prove or disprove anytime soon.

I was curious enough to start asking DR GOOGLE some questions and apparently frothing ability is determined by milk protein and its better when the milk has little or no fat content.  According to the Coffee Geek properly prepared milk is always foamed. Incorporating air into the milk improves and sweetens the taste. Milk that has not been foamed at all tends to taste flat and dull by comparison. The quantity of foam you have incorporated into the milk will be dependent on how much is required for the drink and how aggressively you worked to incorporate air into the milk.

Courtesy of the Geek if you want the nitty gritty detail on milk for the novice things can be as simple as this.

  • Non-Fat Milk will be the easiest to foam. It will not however be as decadent a combination with your coffee and for this reason I don’t ever really like to use non-fat milk.
  • 2% Milk will foam quite easily and is a nice balance between ease of foaming and some fat in the milk making for a creamy and tasty drink
  • Whole Milk is going to be the most challenging to create foam with. It will however be some kind of tasty when combined with coffee. The extra fat in the milk makes your latte or cappuccino a special treat.

I agree with the Coffee Geek “It’s not just the coffee; it’s the milk too. The milk is important, treat yourself.”

“Remember that the creation of foam is an admirable goal but it is not the end all and be all. We do not want to create foam at the expense of the larger experience and so my preference is always for a fuller fat milk-always.
In Italy they use whole milk. If you were to order low-fat milk they’ll look at you like you’re some sort of bleeding heart, left of centre liberal freak and obviously a tourist with no understanding of la dolce vita or proper café culture.
If you say nothing and drink the coffee as it is served to you, you will get whole milk, very likely enjoy the whole milk and come back home telling everyone how great the coffee is in Italy.”

When I typed in “what makes milk froth” I got lots of hits and this is the one that I thought explained it best. Find it here and summarised below

When coffee milk does not want to froth, these might be the reasons:

1. Proteins in milk

The protein in milk, especially the whey-proteins, is largely responsible for the foaming capacity in milk. These proteins form a film on the surface of the air bubbles in the foam. heating milk above 60°C causes the proteins to be denatured and it is more efficient in coating and stabilizing the air bubbles. UHT milk froths better than pasteurized milk, more proteins are denatured. Changes in season and what cows eat can negatively affect proteins in milk, and thus negatively effect foaming.

2. Homogenization

Homogenization improves the process of steam frothing

3. Milk fat

In general the lower the milk fat, the more foam will be formed. Skim milk will give the greatest volume of foam. This equation changes slowly when milk fat is raised above 5%. Above this value higher fat will give more foam. Breakdown of fat or lipolysis will negatively affect foaming of milk. Lipolysis generally occurs before the pasteurization of milk and is caused by the enzyme lipase. Lipolyses producers free fatty acids. Free fatty acids are surface-active agents, which depress the foaming capacity in milk. Lipolysis can occur spontaneously in milk and is aggravated by agitation. This will occur when the cow’s level of nutrition is low and when she is late in lactation. This occurs in herds and regions due to feed available. This can happen during a period of adverse weather and when cows are seasonally calved. Lipolysis due to agitation commonly occurs at farm when air leaks into teat cluster and air and warm milk are vigorously mixed in milking equipment. Also occurs in factory when air is incorporated when raw milk is pumped. Lipolysis will also occur if raw milk is mixed with pasteurized / homogenized milk

4. Milk temperature

Low temperature makes milk more receptive to taking in of air

I just hate UHT milk ( those little milk thingys you get in hotel room mini bars that don’t have to be refrigerated YUK ) I cant see for the life of me what permeate might have to do with frothing, but I love a great coffee made with full cream milk and some days its easier than others for the cows to help you put the froth on the top

and this great little video from BuzzFeedBlue

Coffee Around The World

2 thoughts on “What makes milk froth?

  1. Full cream milk (preferably unhomogenised and organic) all the way for me!! My lattes are a daily treat. I used to have goat milk lattes (you do get used to the taste of goats milk eventually) before it got ridiculously expensive! Very informative blog. Thanks! 🙂

  2. Interesting to read the science behind what we experience at our Cafe every day. If you want to want to generate a lot of foam for a babycino, best to use lite milk! Also noted that light milk makes for a much thicker milkshake. By the way Lynne, cool baristas call their foam ‘silk’.

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