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I froth my milk using the steam wand on my espresso machine. With a national-brand organic whole milk, I am able to get a perfect micro foam nearly 100% of the time. However, when I instead use a local, grass-fed, organic whole milk (whose flavor I prefer to the national brand), I am only able to produce a perfect micro foam about 20% of the time. What could be causing this? Could it be differences in the fat content? (They are both labeled "whole".) Does it have something to do with the fact that the national brand was likely from grain/corn-fed cows, whereas the local brand is grass-fed?

Update: The local milk is homogenized and pasteurized. It does not say anything about ultra-pasteurization (i.e., HTST vs. ESL). The "national brand" milk is homogenized and apparently comes in both "pasteurized" and "ultra-pasteurized" forms. I'm not sure which one I usually get, but if I had to guess I'd say it's ultra-pasteurized (i.e., ultra-heat treated) because the national brand usually has a sell-by date at least a week after the local milk's expiration. According to their nutrition labels, both have the exact same nutritional content except:

  • Sugar (per cup)
    National: 11g
    Local: 12g
  • Cholesterol (per cup)
    National: 30mg
    Local: 35mg
  • Vitamin C (% of Daily Value per cup)
    National: 0%
    Local: 4%
  • Vitamin A (% of Daily Value per cup)
    National: 4%
    Local: 6%

Protein content is reported as identical.

Update #2: As I mentioned in a comment to TFD's answer, I let the local milk age for several days and now I seem to be getting better results (although I am now at the cusp of its sell-by date). Perhaps there is some psychological effect going on and I am paying more attention to my technique now, though. If in fact this success is due to the aging, can anyone explain why? What happens over time that allows the milk to froth better?

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Are both homogenized, or only one of them? And what about pasteurization temperature? (Homogenized should form a more stable foam. ESL will break down more proteins as compared to classic pasteurization). –  rumtscho Jul 20 '11 at 12:25
    
Both are homogenized. I'll check the pasteurization temperature once I get home today. –  ESultanik Jul 20 '11 at 12:55
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3 Answers

up vote 1 down vote accepted

Let your milk age a bit; a day or two extra in the fridge should fix the problem.
Your local milk is too fresh.

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Perhaps there is some psychological effect going on and I am paying more attention to my technique now, but I let the local milk age for several days and now I seem to be getting better results (although I am now at the cusp of its sell-by date). If in fact this success is due to the aging, can you explain why? What happens over time that allows the milk to froth better? –  ESultanik Jul 26 '11 at 12:23
    
Despite the fact that I am still not 100% sure why this happens, I am marking this as correct because it basically solved my problem. My working theory is that the milk's proteins denature over time, which allows for better foaming (much in the same way that egg whites foam better when acidic cream of tartar is added to denature some of the proteins). –  ESultanik Aug 25 '11 at 19:33
    
@ESultanik in NZ we have milk products designed just for latte's (microfoam). When cafe's order it they can get it pre-aged. It works because...um err, I don't think anyone really knows why, it just does :-) –  TFD Aug 27 '11 at 11:27
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Check how much protein your milk contains, that makes the main difference in the behaviour of the milk during frothing. See CoffeeGeek for a more detailed explanation.

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This is a great link. But our guideline is to summarize the relevant info in the answer, as a precaution against linkrot. Do it, and I'll be very happy to upvote you. –  rumtscho Jul 21 '11 at 9:54
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If you want to make milk froth/foam for using with espresso, you should put 0% fat milk in a blender/mixer; this produces a very thick foam.

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From what I understand (perhaps I am misinformed), that procedure will produce a "dry macrofoam." I am trying to produce a "wet microfoam." –  ESultanik Jul 23 '11 at 22:14
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