I recently found out that a friend of mine has been buying raw milk for his own consumption at home, and it sparked an idea for a little taste experiment: why not try my hand at home pasteurization using a water bath/sous vide? I'm curious mainly from a coffee nerd's perspective, as milk is a very common ingredient in coffee beverages. Often however the milk used in cafes is just whatever is conveniently available from a local distributor - after all, it's way more cost-effective to have your materials delivered to your door instead of paying an employee to run around town hoping to buy enough milk for the day/week. But to simply use the convenient option could be missing out big time in the flavor department, right? So, I set myself up to see how pasteurization affects milk flavor, testing two different time/temp combinations against the raw milk itself.
Referring to the FDA guidelines on milk pasteurization, I picked two pasteurization points: 145 F for 30 minutes, the lowest option afforded by the guidelines, and a sort of hybrid point on the curve at around 180 F for 60 seconds. The latter option was a difficult hurdle to manage because commercial pasteurization uses vastly different equipment than what I have at my disposal. It is entirely possible for a dairy processor to squirt milk through heating and cooling tubes such that the liquid hits a uniform 191 F for precisely 1 second before rapidly cooling. Since I'm pasteurizing milk in a bag-within-a-bag in a water bath, I had to settle for rapidly raising the temp to 180 F over a minute, then chilling the bag in an ice bath. This results in over-pasteurized milk, to a slight degree, but I wasn't attempting to rigorously find a drop-off in flavor, rather I wanted to note the degree to which flavor can change from its raw state thanks to heat treatment.
The results were telling: the raw milk presented a very sweet character, with a strong hint of vanilla and floral honey, and a grassy, haylike finish (barnyard). The low-temp pasteurized milk was very similar in flavor, but had a bit more of a rich vanilla ice cream flavor to it, and finished cleaner and sweeter than the raw. This was my favorite milk of the bunch. The high-temp pasteurized batch lost a good deal of sweetness (though it wasn't not sweet), taking on a slight metallic taste and astringency, and a more present haylike flavor. It tasted simultaneously flatter and sharper, as the fullness of the creamy sweetness was diminished, replaced instead by obvious taste defects. I would say it tasted slightly scalded, but not as obviously so as boiled milk would have been.
The other half of this trial was to compare performance when being steamed for a latte or cappuccino. I steamed a few batches myself, and also had a barista friend try steaming all three. There were slight differences between the batches, but nothing major and nothing that prevented getting good quality microfoam. I've steamed other raw milks before and had trouble getting foam to form and stay put, but I think that's more about the condition of the cream - I've had the same problem with pasteurized creamtop milks, usually because the cream has settled out and crystallized a bit. Fat is very necessary for good microfoam in steamed milk, and I think creamtop milks can have an issue where the fat has settled out and won't reintegrate easily without heat or homogenization. Unmelted fat crystals cause the foam to rapidly collapse, as does the absence of fat unless you've created a coarse, dry foam (undesirable in most of the specialty coffee world).
Regardless, it was a fun experiment and I thought I'd pass the info on. Raw milk is rather expensive where I am, so I'm not likely to play with it too much more, but I'd be interested in seeing what others might make of it.
