Ultrasounds accelerate extraction processes due to acoustic cavitation [8], [9]. When acoustic bubbles, also called inertial bubbles, collapse near solid materials, such as coffee grounds, they generate micro-jets with the force to fracture the cell walls of plant tissues, intensifying the extraction of the intracellular content [10].
Seems more involved than just aggressive stirring.
Yes, that is exactly how ultrasonic cleaners are used, it basically gets abrasive on the surface (like scrubbing with like a hammering motion, but on a tiny level).
The size of the bubbles is determined by the frequency (the higher it is the smaller the bubbles with lower energy each, the lower it is the bigger are bubbles and more powerful each).
So, if you are cleaning a large flat metal sheet, then you can go lower frequencies to speed up the process, whereas you would want higher frequencies for more intricate objects so the amplitude is smol enough to get into all the tight spaces for bubbles to form.
38kHz is a very common for ultra cheap household various purpose cleaner (jewellery, fruit & veggies, glasses, delicate clothes, etc), I have a 50kHz buttplug shaped one (so you put in a container and is not itself part of one).
That’s not exactly what it’s doing. Cavitation is when when the pressure of a liquid reduces below the vapour point. Heat isn’t involved the liquid “boils” because the vapour point decreases with reduced pressure.
🤷♂️ Tomato / Potato. Cavitation occurs (the bubble formation) at a temperature below 100C, yes. As the steam bubble shrinks, very high temperatures are reached (super-heated steam). All of that energy, plus the latent heat of condensation is released back into the fluid. At that instant, there is a very small yet-to-be-mixed portion of liquid that may be near the boiling point. That small portion of fluid may undergo a warm-brew process as it cools and mixes. I’m kind of conceptualizing this brewing process like: what if you could heat, mix, and cool the coffee all at once everywhere. But I’ve never observed cavitation and bubble collapse with an ultra high-speed microscope camera, so my concept may be off a bit. I have seen photos of what it does to hardened steel hydropower turbines.
My next question would be, what if you start with ice water? That may give you something like true cold-brew. Another factor to consider is that I believe most cold brew is very oxidized. It might be interesting to try ultrasonic degassing for some period of time before the grounds are added, to see how much of the cold brew flavor is just oxidized coffee.
From the paper.
Seems more involved than just aggressive stirring.
https://www.sciencedirect.com/science/article/pii/S1350417724001330
Yes, that is exactly how ultrasonic cleaners are used, it basically gets abrasive on the surface (like scrubbing with like a hammering motion, but on a tiny level).
The size of the bubbles is determined by the frequency (the higher it is the smaller the bubbles with lower energy each, the lower it is the bigger are bubbles and more powerful each).
So, if you are cleaning a large flat metal sheet, then you can go lower frequencies to speed up the process, whereas you would want higher frequencies for more intricate objects so the amplitude is smol enough to get into all the tight spaces for bubbles to form.
38kHz is a very common for ultra cheap household various purpose cleaner (jewellery, fruit & veggies, glasses, delicate clothes, etc), I have a 50kHz buttplug shaped one (so you put in a container and is not itself part of one).
Cavitation is literally boiling, but the bubbles of steam are tiny, only last for an instant, and then collapse and cool back into the fluid.
That’s not exactly what it’s doing. Cavitation is when when the pressure of a liquid reduces below the vapour point. Heat isn’t involved the liquid “boils” because the vapour point decreases with reduced pressure.
🤷♂️ Tomato / Potato. Cavitation occurs (the bubble formation) at a temperature below 100C, yes. As the steam bubble shrinks, very high temperatures are reached (super-heated steam). All of that energy, plus the latent heat of condensation is released back into the fluid. At that instant, there is a very small yet-to-be-mixed portion of liquid that may be near the boiling point. That small portion of fluid may undergo a warm-brew process as it cools and mixes. I’m kind of conceptualizing this brewing process like: what if you could heat, mix, and cool the coffee all at once everywhere. But I’ve never observed cavitation and bubble collapse with an ultra high-speed microscope camera, so my concept may be off a bit. I have seen photos of what it does to hardened steel hydropower turbines.
My next question would be, what if you start with ice water? That may give you something like true cold-brew. Another factor to consider is that I believe most cold brew is very oxidized. It might be interesting to try ultrasonic degassing for some period of time before the grounds are added, to see how much of the cold brew flavor is just oxidized coffee.