Today's post comes to you courtesy of Mary Roach (aka, the person I want to be when I grow up). I have a copy of her latest book, Gulp: adventures in the alimentary canal that I am reading for review, and a weird science connoisseur such as myself of course spends half her time in the bibliography section, wherein I located this paper. This paper may thus be taken as a pre-review of the book. Spoiler: so far, the book is FABULOUS, but should never be read while eating.
Ah, goat milk. When I think of goat milk, I think of places like farmer's markets, Whole Foods, and little Heidi dancing through the alps. I'll admit to never having drunk raw goat milk (though I do LOVE goat cheese). But after having read this paper, I'm afraid that I do not WANT to try raw goat milk. Why? I'm afraid of the taste...the goaty taste...that is potentially hot, sexy goaty hormones. Hot sexy goat hormones sprayed around in hot, sexy goaty URINE.
Smith et al. "Characterization of Male Goat Odors: 6-Trans Nonenal" Journal of Dairy Science, 1984.
(Awwww. Just wait til he pees all over himself... source)
So, goat milk doesn't usually taste...well, goaty. Usually it tastes pretty much like cow milk (whole fat cow milk, that is). But sometimes, you'll get a bad batch. Nothing's WRONG with it, per se, it's still healthy and not bad, but it's...goaty. The flavor and smell are musky and weird, and not at all tasty. So obviously you want to find the source of that problem.
For years, people who raise goats have pinpointed the MALE goat as the source of the issue. Male goats smell very goaty indeed, particularly during the goat mating season (the rutting season). Some of the odors they emit are so strong they can be smelled several hundred meters away. The odors are very volatile, so they will spread easily, and the idea has long been that if your male goat is around the ladies, his manly odors will get on them and in them, and thus in their milk, resulting in goaty milk (which, if the male goat is the cause, means that goaty milk is really just...MANLY). So goat farmers usually keep their male goats at a good distance from the females during the rutting season, to keep the males from getting their...manliness in the milk. Manliness is just not very tasty.
But of course, even if the chemicals the male goat is producing are volatile, how do you get them in the air in the first place? Well, the male goat in rut has a truly lovely hobby of spraying urine all over himself and his scent glands (which are, in fact, on his HEAD). Nice urine bath to get all those chemicals in the liquid, and thus in the air (This has easily persuaded me to never touch a damp looking goat).
But the important question is, what ARE the chemicals that give these manly goats their manly smell (and can you market them in Old Spice?)? After all, knowing what they are could make it that much easier to keep them out of the lady goat area in the first place.
So the authors of this study collected themselves a LOT of goaty secretions. The authors first tried sampling the air in the barnyard...but had a problem with contamination due to that pervasive "barnyard odor". So much for the clean method. They had to swab some buck goats directly. Buck goats. In rut. Covered in their own urine. And smelling goaty. The things we do for science.
Then followed a lot of chromatography and isolation to determine what volatile compounds they had. They ended up with a few major potential culprits: 4-ethyl octanoic acid, 4-methyl octanoic acid, 4-ethyl oct-2-enoic acid, and 6-trans nonenal. 6-trans nonenal was a funny one, 6-cis nonenal is actually one of the chemicals that produces that nice melony smell in melons like honeydews. In a quirky twist of chemical fate, the cis smells like the sweet melon from the body shop, and the trans smells, at best..."musty".
So we have these four chemicals. All are volatile, all are fairly potent. Which one is our goaty culprit?! Bring in the taste test! They authors had a panel taste goat milk, with the different chemicals, isolated from all that swabbed goaty URINE. I can see this selling right now "Hi! would like to try some goat milk for our study? We're going to be including different compounds we've isolated from male goat urine to find out which tastes the worst! Wait! Where are you going?"
(The taste of science. Sometimes sour, sometimes sweet. Source)
Anyway, a panel of brave volunteers tried different glasses of goat milk with different added compounds, and rated them on things like "goaty", "rancid", "melon-musky", and "other". The different categories were more than a little bit leading, but they got their answer. The 6-trans nonenol was the most potent, but produced a flavor that was melony-musky. NOT goaty. The goaty culprits were a mix of the 4-ethyl octanoic acid, 4-methyl octanoic acid, and 4-ethyl oct-2-enoic acid.
Of course, these are probably not all the culprits, as the authors note "A thorough investigation
of "goaty" flavor is beyond the scope of this
paper". But knowing a few of the chemicals involved is useful to know where that goaty smell is getting in your milk. So hopefully, a full panel of goaty milk chemicals will someday be published for our reading pleasure. Though it might be difficult to find volunteers.
Smith, P., Parks, O., & Schwartz, D. (1984). Characterization of Male Goat Odors: 6-Trans Nonenal Journal of Dairy Science, 67 (4), 794-801 DOI: 10.3168/jds.S0022-0302(84)81369-7