Food Chemistry
Why won’t my milk foam?
The problem we have with milk is that drinkable doesn’t necessarily mean foamable. Many people tell me that they find skimmed milk easier to foam than full fat, and yet we know that it is all about the protein when it comes to milk foam. Are these people right? Yes and No.
A great and simple test the quality of your milk is to foam it up and then start to listen to it. That’s right - get your ear right into the pitcher. What do you hear? If your milk is in poor condition then it will sound like a freshly opened soft drink, almost fizzing away in pitcher - this is not good. Every tiny pop is another bubble bursting and your foam is falling to pieces. As you let it sit you notice that out of nowhere there are larger bubbles appearing at the edges of the pitcher. With great milk you’ll only hear a few little pops (though this will increase as you swirl the pitcher) but it should really be very quiet indeed.
What has this got to do with full fat and skimmed milk? The answer is down to what is causing your bubbles to burst. It isn’t down to drainage as we see in crema, but the presence of glycerol. Glycerol provides the backbone to our triglycerides in our fat molecules - making up around 4% of our whole milk but only traces in our skimmed milk. When the milk is fresh the glycerol is busy being part of a bigger fat but various things can break it up letting it run free. Free glycerol interrupts the foaming process very effectively causing our bubbles to burst. So full fat milk is more susceptible to this than skimmed. However when the milk is fresh this shouldn’t be a problem for either product.
Often we can trace the problem back to storage. The big enemies of foamable milk is light and heat, so if you get your milk in a clear glass bottle that has been exposed to the morning daylight for some hours before delivery then it is likely to be in pretty poor condition. Again - light is a problem in some cafes where they store it in a glass pitcher in a glass fronted fridge. Store it somewhere dark and nice and cool. Interestingly the longer life fresh milks now come in more opaque packaging than many standard milks on the market. In the UK milk in a supermarket never really has more than 10 days shelf life but I tend to see a sharp dip in foam quality when you get with three of four days of the use by - even though it tastes great with my cereal. Anywhere along the way from cow to cup someone can ruin the milk, so it is hard ever to definitive in saying one dairy is better or worse than another.
We are starting to see more and more “Cappuccino Milks” on the market. Often they have added protein (which we already have plenty of to start with) or in one bizarre case they have removed half the fat and then added thickeners and stabilisers to get the nice thick viscosity of full fat milk. This is also a UHT product which I am not wild about. If we look at the quantity of protein in the milk it is around 3% by weight. However only about 25% of these are whey proteins which are the ones that we are after. If you are choosing a milk for cappuccino then taste, sweetness and a creamy texture are what you are looking for in the raw product but often we just don’t demand the same of our milk supplier as we do our coffee supplier - yet your average cappuccino is way over 80% milk. We don’t think of it as a point of difference - milk is milk right? Try it - go out and buy 5 different brands of milk. Steam them all. How do they perform? How do they taste?
Any questions in the comments….
[tags]milk, cappuccino, milk chemistry, food chemistry, lipids, latte, latte art[/tags]
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Hello Jim,
Nice post, and great blog. What’s your take on the ultra-pasteurized organic milks? How do they compare to “regular” milks?
Fizzy, rapidly disappearing foam is one of my nemeses. I didn’t know whether to ascribe it to poor technique or bad milk. This post would seem to point toward the latter. It can be frustrating…
Thanks!
Howard
It does depend on technique too. If your technique results in larger bubbles then they will naturally be weaker than dense microfoam. Check the dates on your milk, try a few different brands, check your boiler produces enough steam power to get the small bubbles needed for microfoam.
As long as pasteurisation has been done properly there should be no impact on the milk, organic is fine usually.
hi, have you played with any non cow milks? goat, sheep, yak, human? i’ve been prommised some raw goats milk and i was wondering if it’d be worth a play.
also, does freezing have an impact?
Goat - yes, Human - er, no.
Just about any milk with a similar protein content to cow’s milk (3%) should be ok. This goes for goat, sheep, yak, reindeer or whatever you can find at the zoo. I can only presume it is the same for human milk too. Some of the ones with much higher fat contents might be tricky, but I would be more worried about the taste.
I did once serve someone a goat’s milk capp. It did not go down well….
Ha! Love it!
Hi,
1. You’ve mentioned “big” fats, do you mean larger molecules?
2. Also the process of homogenisation playing a role in the breakdown of fat, as the process is appears to be destructive?
3. Constitution of skim is mostly water, as I am lead to believe… what about the use of cream? Now that’s an idea, perhaps… why be worried about the taste? People love fats, cream is used in all types of cookery, desserts, drinks, cocktails. Dairy in the vast majority of coffee drinkers opinions go well together. Apparently in the US they use half’n’half though unhealthy it would certainly taste good IMHO.
Pascal
I forgot to ask, is this only on commercial machines that you are talking about? Is there a diffence between steaming and machines ie pressure, no. of holes in steaming wand etc..
Haven’t seen “cappuccino milk” on these shores yet.
At some point milkfoam will begin to “bubble” on the edges if left to sit, no matter how good the microfoam - in your trials, have you identified an “ideal” time period before this happens? And what milk/milkfat delivered the longest time before bubbling? Or are you suggesting it has more to do with age of the milk than any other factor?
Human milk… heh… well, here’s an idea, “Ma’am, if you care to contribute some milk for everyone in line, we’ll give you a free refill. Here’s a pump…”
Firstly, slightly off subject, I feel the need to thank Jim/James and Annette for their boundless enthusiasm and knowledge that keeps life interesting for us all.
Secondly…milk stuff. I feel the need to agree and disagree with this thread. We buy milk from a local farm, near our roastery. The cows are Danish bread Jersey’s so the milk is approaching 6-7% Wholesome.
( The UK government have actually been talking about taxing fat in milk…to stop children in inner cities drinking cola or something…)
Anyway…This milk is trully “old fashioned” and makes my milk based drinks amazingly sweet, although I can’t drink so many a day, otherwise the ripples begin to show etc. yuck!
In recent weeks the cows have come in their food has changed and I have had to go back to the irradiated blue stuff from the super market, because the milk will take NO air or if it does it will fizz and make large square bubbles. The couple who run the farm (and dairy) have tried pasterising the milk for longer for us, but still we will wait until spring.
Of all the things you can say about mass market milk (or may be anything) it is that it’s consistent.
Happy Christmas Mr. Hoffmann
I agree with Peter J. In Australia there are certain times of year where the milk just will not foam.It comes down to the varying diet that cows have in southern hemisphere.(They feed on grass outside all year round) The cow’s diet here in the Northern Hemisphere may be more consistant as they are not eating grass outside all year round. I agree with the storage concerns but I think diet may come into it.
I agree with Peter J. In Australia there are certain times of year where the milk just will not foam.It comes down to the varying diet that cows have in southern hemisphere.(They feed on grass outside all year round) The cow’s diet here in the Northern Hemisphere may be more consistant as they are not eating grass outside all year round. I agree with the storage concerns but I think diet may come into it.
Actually, Mary, my understanding is that, during summer the cows are considerable more stressed - due to the heat conditions, and this has a dramatic impact both upon production and quality.
I tell my customers that it also has something to do with ‘clover in pasture’ which may or may not be the case, but at least it makes you look like you know what you’re talking about!
Also, with the extra heat, storage and transportation may well be an issue.
Happy Christmas to you too Peter!
Ok - here is a quick test if your milk won’t foam. Overheat it and see how it smells. If there is that baked, slightly eggy smell in it then there was the right protein in the milk - as it is an amino acid (cysteine) that contains the sulphur that has been released through the breakdown of the protein (beta-lactoglobulin) as H2S (a not very pleasant gas).
Of course other proteins are likely to have this amino acid (I can’t pretend to know the amino acid sequence of every milk protein!) but it can only be liberated from whey proteins as they are the only ones temp sensitive below 100C.
If that makes sense?
Why is it that sometimes my milk will foam properly but then when I pour it on the coffee it starts fizzing and bam, no more foam
I just made 2 cappuccinos. One was perfect, and the other one with the exact same milk fizzled and the foam disappeared.
By the way, I’m using non-fat milk from the supermarket.
Thanks in advance,
Carlos Lage
Just me thinking here, but maybe your textured milk froth started to separate? Sometimes I find that if I let my cap froth sit in the cup, the thicker stuff rises to the top while the creamy microfoam stays relativtely homogenised. With a bit of practice this won’t happen, but in the meantime try ’splitting’ a bit of milk off into a second jug. This keeps the froth smooth and homogenised, and gives consistent proportions in your drinks (ie you’re not pouring all the froth into your first cap and giving the second one nothing but milk).
Cheers
Josh
good luck!!很好啊。
I have noticed more and more consistently that here in the US (Pennsylvania), regular non-fat milk never foams properly even the first day, whereas organic milk always does. Any idea why this would be?
Hi, im doing a project concerning the foaming of milk, what are the various ways in which triglycerides can breakdown?:
‘When the milk is fresh the glycerol is busy being part of a bigger fat but various things can break it up letting it run free.’
This would be a great help thanks
I’m actually having this exact problem with Horizon Brand organic skim milk(I live in Central Ohio). I wonder whether it could have anything to do with freshness (since my milk is also UHT pasteurized I really have no idea how long it has been sitting in storage/at the supermarket) since it is non-fat. All I can say is that I switched recently due to lack of availability of an organic and local brand that had served me well in the past, but I’ve had a lot of falling cappuccinos since then.