Why did my homemade hot chocolate separate into "slime"?

I made it with whole milk, a little half and half, bittersweet chocolate, cocoa powder, sugar, cinnamon, chili and cayenne. It was fine at first but after I heated it up a little later while whisking continuously, the bottom third developed into a viscous dark chocolate slime. It's the weirdest thing. I've never had that happen and am not sure what caused it.



Lori T. March 15, 2022
Although we think of chocolate milk and hot cocoa as being a mix, where the multiple things sort of morph onto one- the thing is, it's not. It's a suspension, kind of like oil and vinegar salad dressing. The cocoa powder is actually a lot of tiny bits which don't much like water. They would prefer to mix it up with a fat, which they do in your mix, with the butterfat molecules in the cream of the half and half. And being heavier, they sink to the bottom of your mix over time, taking fat molecules along with the cocoa bits. That's what your "slime" is. The immersion blender would help because it would bust up the party, and break the fat molecules and cocoa bits into smaller bits which will hang out in solution a little longer next time.
LRBrincks March 15, 2022
Thank you! I wonder if it’s the half and half (fat) that I added at the end that made it react so differently this time. I’ve had it separate before but never with this consistency and that I couldn’t reconstitute. Also, I heated and whisked it for a long time to get a thick European style hot chocolate which I assume reduced the water content leaving a higher ratio of fat and chocolate.
Lori T. March 15, 2022
I don't think it would matter when the cream is introduced into the mixture. It has to do with the size of the fat particles. Homogenized milk stays separate because the process breaks them into tinier bits. It then distributes the bits more evenly in the rest of the liquid. Over time a certain amount of fat will still rise to the top, but generally your milk is either gone or sour by then, and you don't care or notice. The big secret to a thicker European style hot chocolate actually lies in using cornstarch to thicken and stabilize your mixture. Reducing the amount of water in your hot chocolate because you cooked it for a long time would not change the size of those cocoa powder and fat molecules though. It just meant they had less liquid to displace as they sank. If you make salad dressing, reducing the amount of vinegar doesn't change the fact that your onion and herb bits still sink to the bottom, or that you can't keep the vinegar/water and oil mixed together with all the seasonings. You have to have an emulsifier to do that - mustard in the case of a vinaigrette, egg yolks for mayonnaise - and cornstarch for hot chocolate.
Nancy March 15, 2022
Lori - thanks for the chemistry reminders!
That's why I don't get sludge if I drink the cocoa right after heating or with benefit of the blender.
The cocoa and fat attractions still there, but doesn't have time to bind.
Nancy March 14, 2022
It happens to me sometimes - a coalescing of some undissolved chocolate matter at the bottom of the cup, though not so bad as slime - if I don't mix thoroughly or drink while still hot.
I do two things to prevent this occurring:
1) mix a small amount of cocoa powder with (cold) milk before adding hot milk or heating the whole mixture.
2) make the cocoa paste as in #1, but also blend mechanically - blender, processor or the like. Especially worth it if you're making a batch, not just one cup.
Also here are some tips to avoid lumps, which may help in preventing future slime.
LRBrincks March 14, 2022
Thanks, Nancy! I'll try using hand blender if it happens again to see if I can reincorporate it.
jnm,okl April 15, 2024
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