Conservation of Heat
June 24, 2013 6:02 PM Subscribe
I read a method for making iced coffee that set off my bullshit detector. The gist of it was "if you put ice in a bunch of hot coffee it will melt and you will have warm liquid", but! "if you brew drip coffee over a pot of ice, since there is only a small amount of hot coffee hitting the ice at each moment, you will have lots of cold coffee!". That's bunk, right?
If you brew X oz's of hot coffee, it contains Y energy. It doesn't matter if you slowly apply Y energy to a quantity of ice, or quickly apply the same Y amount of energy to ice, right? (In fact, to get pedantic, it seems like it would be worse, since if you brewed all the coffee first, it would bleed a bit of heat off before you added the ice.)
If you brew X oz's of hot coffee, it contains Y energy. It doesn't matter if you slowly apply Y energy to a quantity of ice, or quickly apply the same Y amount of energy to ice, right? (In fact, to get pedantic, it seems like it would be worse, since if you brewed all the coffee first, it would bleed a bit of heat off before you added the ice.)
But I can tell you that 3 quarts of water drip-brewing directly onto onto 3 quarts of ice makes ice-cold tea.
posted by bleep at 6:10 PM on June 24, 2013 [1 favorite]
posted by bleep at 6:10 PM on June 24, 2013 [1 favorite]
It's especially bunk since heat should not be involved in making iced coffee. Add the coffee grounds to cold water, place in the fridge for 12-24 hours, filter and serve. The long, cold extraction results in a rich but nearly acid-free beverage that will actually benefit from any watering-down that occurs from the addition of ice.
posted by bizwank at 6:18 PM on June 24, 2013 [15 favorites]
posted by bizwank at 6:18 PM on June 24, 2013 [15 favorites]
Wait, but when you brew onto the ice cubes you have little bits of hot coffee added to a big thing of ice and at each moment it's losing heat. So instead of one big pot of hot+cold reaching equilibrium you have a series of (squirt of hot coffee)+ice, 2(squirts of hot coffee)+ice, and so one. I don't know, just try it already.
posted by silvergoat at 6:22 PM on June 24, 2013 [1 favorite]
posted by silvergoat at 6:22 PM on June 24, 2013 [1 favorite]
bizwank is correct - that method makes delicious iced coffee but I still think you should try it and report back.
posted by silvergoat at 6:23 PM on June 24, 2013
posted by silvergoat at 6:23 PM on June 24, 2013
Response by poster: It's especially bunk since heat should not be involved in making iced coffee. Add the coffee grounds to cold water, place in the fridge for 12-24 hours, filter and serve. The long, cold extraction results in a rich but nearly acid-free beverage that will actually benefit from any watering-down that occurs from the addition of ice.
This was specifically a hot-brew-to-make-iced-coffee method. But yes, you can also cold brew. (IMHO cold-brew tastes gross, Chemex supremacy!) I don't really care about the temperature of my coffee a whole lot, was just pandering to summer. Normally I drink my coffee between hot and room temperature and love it no matter what.
I don't know, just try it already.
I did try it, and ended up with a slightly-steamy Chemex full of just shy of normal strength coffee (slightly overdosed to compensate for the ice). Just wanted to get some physics amens. :)
posted by wrok at 6:27 PM on June 24, 2013 [1 favorite]
This was specifically a hot-brew-to-make-iced-coffee method. But yes, you can also cold brew. (IMHO cold-brew tastes gross, Chemex supremacy!) I don't really care about the temperature of my coffee a whole lot, was just pandering to summer. Normally I drink my coffee between hot and room temperature and love it no matter what.
I don't know, just try it already.
I did try it, and ended up with a slightly-steamy Chemex full of just shy of normal strength coffee (slightly overdosed to compensate for the ice). Just wanted to get some physics amens. :)
posted by wrok at 6:27 PM on June 24, 2013 [1 favorite]
I make iced coffee all the time by pouring hot coffee over ice cubes.
Brewing drip coffee into a pot of ice sounds like a recipe for shattering your coffee pot.
The most efficient and in my opinion best tasting way to make iced coffee is to brew it cold by adding cold water to room temp coffee grounds and letting it sit -- either at room temp or in the fridge -- overnight.
Pouring hot coffee over ice isn't quite as tasty, and is sort of wasteful if you think about it (first you heat the water and then you cool it, over ice that you had to make expressly for the purpose of melting back down), but it gets the job done.
posted by Sara C. at 6:28 PM on June 24, 2013 [1 favorite]
Brewing drip coffee into a pot of ice sounds like a recipe for shattering your coffee pot.
The most efficient and in my opinion best tasting way to make iced coffee is to brew it cold by adding cold water to room temp coffee grounds and letting it sit -- either at room temp or in the fridge -- overnight.
Pouring hot coffee over ice isn't quite as tasty, and is sort of wasteful if you think about it (first you heat the water and then you cool it, over ice that you had to make expressly for the purpose of melting back down), but it gets the job done.
posted by Sara C. at 6:28 PM on June 24, 2013 [1 favorite]
are you referring to this blog post, perchance? thanks for asking; i was curious.
i think, though, that the blog i've linked to is referring to pourover rather than drip (made in a machine)... can someone clarify?
posted by raihan_ at 6:29 PM on June 24, 2013 [1 favorite]
i think, though, that the blog i've linked to is referring to pourover rather than drip (made in a machine)... can someone clarify?
posted by raihan_ at 6:29 PM on June 24, 2013 [1 favorite]
Best answer: I think what this method is trying to say is that there's a difference between the two methods with regard to the amount of hot liquid vs. the surface area ratio of the ice. If you dump one ice cube into hot coffee, it will melt faster than slowly dripping hot coffee onto the same ice cube. The ice cube in the coffee is completely enveloped in hot liquid, while the dripped-on cube is not exposing its entire surface to the coffee all at once.
However, you will absolutely end up in the same place.
posted by Cool Papa Bell at 6:29 PM on June 24, 2013 [4 favorites]
However, you will absolutely end up in the same place.
posted by Cool Papa Bell at 6:29 PM on June 24, 2013 [4 favorites]
Response by poster: are you referring to this blog post, perchance? thanks for asking; i was curious.
Not that one, but another that also called it the 'Japanese Method', so certainly related/referencing.
posted by wrok at 6:31 PM on June 24, 2013
Not that one, but another that also called it the 'Japanese Method', so certainly related/referencing.
posted by wrok at 6:31 PM on June 24, 2013
It's not a closed system. A lot of heat would escape into the air and the surrounding room as the drops fall into the ice container. This might be a very significant effect if the coffee maker is rigged up far above the ice bucket.
posted by steinwald at 6:38 PM on June 24, 2013 [3 favorites]
posted by steinwald at 6:38 PM on June 24, 2013 [3 favorites]
Cool Papa Bell makes a good point. When I do this, I use six ice cubes, which fill my 16-oz tumbler to the brim. I pour in maybe 10 oz of hot liquid, max. The resulting ice coffee completely fills the tumbler, and the ice cubes are probably half-melted. I make my coffee strong to counteract the extra water from the melted ice cubes.
If you pour hot coffee over one or two ice cubes, that won't be enough to get it cold.
posted by Sara C. at 6:45 PM on June 24, 2013
If you pour hot coffee over one or two ice cubes, that won't be enough to get it cold.
posted by Sara C. at 6:45 PM on June 24, 2013
Best answer: It's not a closed system. A lot of heat would escape into the air and the surrounding room as the drops fall into the ice container.
that's orthogonal to the question at hand - you could just as easily run your drip into an iceless pot from high above and then add the ice later, and you'd still end up in the same place wrt energy transfer.
posted by russm at 7:00 PM on June 24, 2013 [1 favorite]
that's orthogonal to the question at hand - you could just as easily run your drip into an iceless pot from high above and then add the ice later, and you'd still end up in the same place wrt energy transfer.
posted by russm at 7:00 PM on June 24, 2013 [1 favorite]
I think this might be a bit of folk wisdom caused by people dropping a few ice cubs into an almost full coffee cup vs adding less coffee to a cup that's full of ice cubes, and noticing that, duh, when you have more ice, it's colder.
posted by empath at 7:26 PM on June 24, 2013
posted by empath at 7:26 PM on June 24, 2013
I will bet money that this stems from a conflation of cooking theories. In some circumstances it does make sense to slowly add a hot thing to a chilled thing, but it usually involves chemical changes like tempering eggs. In that case, you would add a small amount of hot liquid to your room temperature eggs to warm them without cooking them, then add the eggs to your batter.
There's also the milk-first and milk-second debate, where the thinking goes that adding milk to your cup before your coffee will allow the cold milk to slowly warm as you pour in the coffee, rather than shocking and curdling the milk by pouring it in to a hot cup of coffee.
posted by backseatpilot at 7:39 PM on June 24, 2013 [1 favorite]
There's also the milk-first and milk-second debate, where the thinking goes that adding milk to your cup before your coffee will allow the cold milk to slowly warm as you pour in the coffee, rather than shocking and curdling the milk by pouring it in to a hot cup of coffee.
posted by backseatpilot at 7:39 PM on June 24, 2013 [1 favorite]
Crazy idea time: could you brew hot coffee to slowly drip into a large funnel or colander full of dry ice, itself over a collection receptacle? You'd get rapid cooling of the beverage but it wouldn't water down, and your byproduct would just be a bunch of gaseous CO2.
And a bonus fog machine
posted by a halcyon day at 8:14 PM on June 24, 2013
And a bonus fog machine
posted by a halcyon day at 8:14 PM on June 24, 2013
I don't know how big the effect is, but you will lose heat to the air if you expose a lot of surface area of the coffee to the air. I used to work with a Colombian guy who would pour his fresh-brewed coffee back and forth between two cups, making the stream as thin and as long as possible, which he said helped cool it off.
So strictly speaking there is a difference. Whether the loss of heat to the air from the individual drop during the time they fall is appreciable I have no idea.
posted by benito.strauss at 8:25 PM on June 24, 2013
So strictly speaking there is a difference. Whether the loss of heat to the air from the individual drop during the time they fall is appreciable I have no idea.
posted by benito.strauss at 8:25 PM on June 24, 2013
Crazy idea time: could you brew hot coffee to slowly drip into a large funnel or colander full of dry ice, itself over a collection receptacle? You'd get rapid cooling of the beverage but it wouldn't water down, and your byproduct would just be a bunch of gaseous CO2.
Probably also no small amount of dissolved CO2, but if you like fizzy coffee, go nuts.
posted by Johnny Assay at 9:02 PM on June 24, 2013
Probably also no small amount of dissolved CO2, but if you like fizzy coffee, go nuts.
posted by Johnny Assay at 9:02 PM on June 24, 2013
Crazy idea time: could you brew hot coffee to slowly drip into a large funnel or colander full of dry ice
I don't think you'd need to drip it all. Just dump the coffee on the dry ice, as it's much colder than water ice. You're right to say that would cool it without diluting it.
posted by Cool Papa Bell at 9:03 PM on June 24, 2013
I don't think you'd need to drip it all. Just dump the coffee on the dry ice, as it's much colder than water ice. You're right to say that would cool it without diluting it.
posted by Cool Papa Bell at 9:03 PM on June 24, 2013
what if it was dry ice surrounding the edge of the funnel and chilling the coffee and it passed through?
posted by raihan_ at 9:08 PM on June 24, 2013
posted by raihan_ at 9:08 PM on June 24, 2013
Fill a mug full of hot coffee, then add ice until just before it overflows. You have still-warm coffee. Fill a mug full of ice, then drip-brew coffee into it until just before it overflows. You have colder coffee. But the former uses more coffee and less ice, the latter uses much more ice and less coffee. It's just an illusion.
Now, if you do it with a Vietnamese drip filter which produces much stronger coffee much slower, you'll end up with colder coffee. But this is true whether you drip it into the cup of ice, or add the ice later.
posted by WasabiFlux at 9:20 PM on June 24, 2013 [1 favorite]
Now, if you do it with a Vietnamese drip filter which produces much stronger coffee much slower, you'll end up with colder coffee. But this is true whether you drip it into the cup of ice, or add the ice later.
posted by WasabiFlux at 9:20 PM on June 24, 2013 [1 favorite]
Try this: dispense espresso into a small cocktail shaker. Add ice, shake vigorously until shaker feels cold to the touch, then pour into a chilled glass. The volume will double from the added water but it will also be very cold and frothy and fabulous on a hot day. If you like it a little sweet add sugar to the shaker before brewing, it will be dissolved by the time you pour.
posted by bizwank at 9:45 PM on June 24, 2013
posted by bizwank at 9:45 PM on June 24, 2013
Liquid nitrogen is a better choice than dry ice, though if you use too much, you'll end up with coffee ice instead of iced coffee. I've (amazingly) never tried it....
posted by JMOZ at 4:08 AM on June 25, 2013
posted by JMOZ at 4:08 AM on June 25, 2013
I use my French press pot to cold brew overnight. The resulting nectar is already chilled, though it heats up just fine. There are plenty of recipes online with proper coffee:water ratios, but I add a bunch of coarsely-coffee to the pot and fill it with cold water, then leave it in the fridge overnight.
N.b.: dilution is often necessary to avoid heart palpitations...on those days that I don't actually want heart palpitations from my coffee.
posted by wenestvedt at 7:51 AM on June 25, 2013
N.b.: dilution is often necessary to avoid heart palpitations...on those days that I don't actually want heart palpitations from my coffee.
posted by wenestvedt at 7:51 AM on June 25, 2013
Took this question to my local coffee joint, their response:
So if you're pouring hot over ice, we suggest using half the hot water for the same amount of coffee. It's quite tasty.posted by raihan_ at 4:02 PM on June 25, 2013 [1 favorite]
raihan_, that is how I make my iced coffee. I have this coffee maker, and it actually has one set of marks for water level for regular coffee, and another set for making iced coffee. The iced coffee marks call for a lot less water but the same amount of grounds, so it results in super concentrated coffee. Then when you pour it over the ice, it melts a few of the cubes and the result is a perfect cup!
posted by orangek8 at 12:59 PM on June 28, 2013
posted by orangek8 at 12:59 PM on June 28, 2013
This thread is closed to new comments.
posted by ssg at 6:04 PM on June 24, 2013 [3 favorites]