First – I’ve googled this repeatedly and only found approximately one million very general results on the order of “What’s that watery stuff on top of my yogurt?” It’s whey. It happens. You pour it off or stir it back in or drink it, I don’t care.
But here’s the thing. I buy Greek Gods brand greek-style yogurt in quart containers, and whenever I open a fresh one there is never any whey. I scoop out a serving, and then the next day the scooped-out area is completely filled with whey. Why not when I first open the container?
It’s not a case of freshness. I’ve bought two containers with the same datestamp, and gone through one over the course of a few days, with the whey experience above, and then opened the second container to find no whey on top. Until the next day, after I’ve scooped from it, of course.
I’m beginning to suspect the surfaces of the filled containers are sprayed with silicone micro-particles, or something, to prevent whey from forming, until I remove the coating by spooning some out. What’s up with that?
Yogurt contains a lot more whey than what you see at the top of the container. If you drain yogurt on a cheesecloth for 12 hours or so, you end up with Labneh, or strained yogurt, which is the consistency of cream cheese.
I think when the container is full, the yogurt is saturated with whey, because there’s no place for the whey to flow down to. But when you scoop out a serving, you create a low point. Whey in the yogurt above that level will drain into that low point.
Yes, it is simple physics. Dig a hole in sand, and water seeps into the hole.
Imagine a yogurt cup of wet sand. The sand doesn’t all sink to the bottom and the water float to the top. It stays mixed together. Dig a hole in the sand and water seeps in.
You might also notice on older yogurt that whey has formed on the sides of the container, and there might be a thin film of whey on the top. It doesn’t separate further because the force acting to separate the whey from the solids is gravity, and the solids are already resting on the bottom of the cup. Where are they going to go?
FWIW I have been storing my cups of Chobani upside-down in my fridge, to let me quickly see which ones are new and which need eaten, and then I turn them back rightside-up and open them, there is whey to mix in.
I also eat Greek God Greek yogurt. It’s the cheapest and best IMHO, at least at Walmart’s. Greek yogurt has no whey. That’s what makes it Greek yogurt, BTW.
Okay, so suppose I scoop out a serving of yogurt, then smooth out what remains so it has a level surface with no “hole in the sand”. Then, no loose whey on top?
(I don’t eat yogurt, actually, and never have any around, but I see much the same thing with cottage cheese.)
Greek yogurt contains less whey than regular, but it still contains some- that’s what makes it scoopable in texture. When you remove all of the whey, you end up with something much ore cheese like in texture.
BTW, I do buy Greek Gods on occasion, but Walmart’s own brand (Great Value) plain Greek yogurt is pretty outstanding as well. I buy the big tubs of it, about a buck cheaper than the Greek Gods brand large tubs.
For those who did not click the link this is a separate hypothesis than the low point one.
The idea is that the yogurt consists of many spheres of proteins with fluid trapped inside. Actually they are large spheres made up of aggregates of smaller ones: larger casein micelles which consist of various numbers of smaller of aggregated casein submicelles.
The implied hypothesis is that scooping out yogurt breaks apart some number of those micelles without enough mixing to re-suspend them.
I suppose if someone wants to bother they can take a cup of yogurt of the same sort that they have observed the pooling after scooping to occur in and give it just a few stirs with the spoon without scooping and return to fridge and then report back after seeing if much separation occurred the next day.
Of some minor note is that “whey” seems to have two overlapping meanings in this discussion: the liquid (aqueous) portion left behind after milk has been subjected to synereresis (e.g. coagulation) consisting of water, one sort of proteins, lactose, and various other compounds, and specifically one component of that aqueous portion - the whey proteins, which do not have hydrophobic tails and therefore do not form micelles like casein does.
The damp sand metaphor also makes a whole lot of sense.