I actually work directly with food scientists. I’ll ask somebody when I’m feeling more myself!
And yes! I learned how to do it yesterday. It’s dummy simple. The most course grind possible is what appears to be recommended. You brew 1 part coffee to 4 parts water in the fridge for 12–18 hours. Then you just strain it. I do not recommend rapid consumption 💀
EDIT: Yeah, it’s the duration. Hot brewed coffee has a not-insignificant amount of caffeine because a smaller grind puts more surface area in contact with water at any given time, and the hot water accelerates extraction of caffeine (and flavor) from the grounds. Cold brewed coffee blows that out of the water, even with a super coarse grind and even at super low temperatures, by virtue of the time involved.
The physics/science of it is essentially that by grinding it very coarse, you are creating a much larger pore space for water to infiltrate. More pore space means larger pores, which means more water in those pockets of coffee grinds to leach out the flavor (and caffeine). It also means less water gets trapped in the pore space when you drain it out.
The way cold brew works is that you are substituting heat for time - heat is essentially ripping the caffeine and flavor from the grounds, and a finer grind will result in a stronger flavor (hence, espresso grind is generally a stronger flavor than standard filter grind). More heat and pressure allows this to be done quicker, which is the principle behind espresso - very hot water forced through tightly packed very fine grounds - done in 10-20 seconds. Cold brew, by contrast, is a slow leaching process. The larger pores hold more water, and you slowly leach the flavor out of the grinds into the water in the pores. The longer you allow it to leach, the stronger the the coffee will be, but also the more bitter it will get. Similarly, the lower the ratio of water:coffee, the more concentrated the resulting brew will be.
Is this due to the duration? Like cold brewing coffee overnight in the fridge? What grind is recommended?
I actually work directly with food scientists. I’ll ask somebody when I’m feeling more myself!
And yes! I learned how to do it yesterday. It’s dummy simple. The most course grind possible is what appears to be recommended. You brew 1 part coffee to 4 parts water in the fridge for 12–18 hours. Then you just strain it. I do not recommend rapid consumption 💀
EDIT: Yeah, it’s the duration. Hot brewed coffee has a not-insignificant amount of caffeine because a smaller grind puts more surface area in contact with water at any given time, and the hot water accelerates extraction of caffeine (and flavor) from the grounds. Cold brewed coffee blows that out of the water, even with a super coarse grind and even at super low temperatures, by virtue of the time involved.
The physics/science of it is essentially that by grinding it very coarse, you are creating a much larger pore space for water to infiltrate. More pore space means larger pores, which means more water in those pockets of coffee grinds to leach out the flavor (and caffeine). It also means less water gets trapped in the pore space when you drain it out.
The way cold brew works is that you are substituting heat for time - heat is essentially ripping the caffeine and flavor from the grounds, and a finer grind will result in a stronger flavor (hence, espresso grind is generally a stronger flavor than standard filter grind). More heat and pressure allows this to be done quicker, which is the principle behind espresso - very hot water forced through tightly packed very fine grounds - done in 10-20 seconds. Cold brew, by contrast, is a slow leaching process. The larger pores hold more water, and you slowly leach the flavor out of the grinds into the water in the pores. The longer you allow it to leach, the stronger the the coffee will be, but also the more bitter it will get. Similarly, the lower the ratio of water:coffee, the more concentrated the resulting brew will be.