Cold Brew vs Iced Coffee: Which One Should You Be Making This Summer?

It’s October, the southeaster has started doing its thing again, and the Popco ice-lolly board has appeared next to the trailer at Big Bay on Sundays (photo below, dog bowl and all). Which, as far as I’m concerned, means iced coffee season has officially started in Cape Town… whether the weather agrees on any given day or not.

Most people’s first instinct for a cold coffee is cold brew. And that’s fine, there’s a lot to like about it. But there’s another way of doing it that a lot of coffee people swear by, usually called flash brew or Japanese-style iced coffee, and it makes a pretty different drink. So I thought I’d go through the whole cold brew vs iced coffee thing properly, because the difference between them comes down to some fairly interesting chemistry (and if you’ve read a few of these posts by now you’ll know I can’t resist that bit).

FYI: I’m not going to tell you one of them is objectively better. They’re good at different things, and which one you want depends a lot on what beans you’ve got and whether you put milk in it.

So what’s the difference?

Cold brew is coffee that never sees hot water at all. You take coarsely ground coffee, leave it to soak in cold (or room temperature) water for somewhere between 12 and 24 hours, strain it, and that’s more or less it. Basically the long soak is doing the work that hot water would normally do in a few minutes.

Flash brew (or Japanese iced coffee, or iced pour-over, it has a few names depending on who you ask) goes the other way. You brew hot, usually on a V60 or something similar, but you brew straight onto ice. The hot coffee hits the ice, melts some of it, and gets chilled within a few seconds. The clever bit is that the ice counts as part of your brew water, so you pour less hot water than normal and the melted ice makes up the difference. If you skip that step and just pour a normal hot coffee over ice you end up with a watery, slightly sad cup, which I’m guessing a lot of us have made at some point.

Anyway, that’s how they’re made. What it does to the flavour is the more interesting part, I think.

Why they taste so different (the slightly nerdy bit)

I studied biochemistry up to honours level. I don’t use it for a living these days, but it’s probably why this is my favourite part of the post, so bear with me.

Basically, temperature changes what comes out of the coffee and how fast it comes out. Hot water is really good at dissolving things. It pulls the acids, sugars, bitter compounds and a whole lot of the aromatic stuff (the volatile compounds you actually smell) out of the grounds pretty quickly. Cold water is a lot lazier about it. Some compounds still dissolve fine in cold water if you give them enough time, which is why cold brew needs all those hours, but others barely come out at all. So the balance of what ends up in your glass is quite different, even with identical beans.

That’s why cold brew tends to taste heavier, rounder, more chocolatey and a lot less bright. The fruity, floral, zingy stuff that makes a good light roast exciting mostly doesn’t make the trip into the cup. Some people love that about it. A fair chunk of the coffee internet finds it a bit flat. James Hoffmann described what the cold brew crowd is after as “heavy, textured, a little sweeter, very low acidity” in an interview with World Coffee Portal last year, and I think that’s a pretty fair summary of what it does well. It also holds up really nicely to milk, which matters if that’s how you drink it.

Flash brew keeps a lot more of the bright, aromatic side, because you’ve extracted it with hot water like a normal pour-over and then chilled it so fast that a lot of those aromatics don’t get a chance to wander off. A fruity Ethiopian made this way can still taste like a fruity Ethiopian, just cold. Made as cold brew, the same coffee usually loses a lot of what made it interesting in the first place.

The “cold brew is less acidic” thing

This one is half true, and it’s a nice example of how something can be technically wrong and still kind of right at the same time. You’ll see it everywhere, usually with “so it’s better for your stomach” stuck on the end.

In 2018 two researchers at Thomas Jefferson University, Niny Rao and Megan Fuller, compared hot and cold brew made from six different coffees, from Brazil, Colombia, Mexico, Myanmar and two regions of Ethiopia (the paper is here, in Scientific Reports, if you’re the type who likes to check). The pH of the two came out pretty much the same, somewhere between 4.85 and 5.13 across the board. So on the scale most people mean when they say “less acidic”, there wasn’t really much in it.

What did differ was the titratable acidity. Very roughly, pH tells you how strong the acid is, and titratable acidity tells you how much acid there is in total. Hot brew had more of it. And that total amount is closer to what your tongue reads as acidity or brightness, which is why cold brew tastes softer even though its pH barely moves. (They also found the hot brew had higher antioxidant activity, for what it’s worth.)

So yes, cold brew tastes less acidic. Is it actually kinder to your stomach? I really don’t know, and I’m a roaster, not your doctor. That study wasn’t testing it, and I’d be a bit wary of anyone who tells you it’s settled.

Quick caffeine side note while we’re on myths: cold brew has a reputation for being way stronger. It can be, but mostly because people make it with a lot more coffee per litre than they’d ever use for a hot brew, and then don’t dilute it much, so it’s really more about the recipe than the method. There are a few more of these in my caffeine myths post if you want more of them.

Cold brew, the lazy way

This is about as low effort as coffee gets, which is a big part of its appeal. A simple starting point:

• 100 g of coffee, ground coarse. Coarser than you’d go for a French press, roughly breadcrumb-ish.
• 1 litre of cold water.
• Mix them in a big jar or jug, give it a stir so all the grounds are properly wet, lid on, and into the fridge for 12 to 18 hours.
• Strain it through a fine sieve first, then through a paper filter (a V60 paper works fine) if you want it clean. This bit is slow and slightly annoying. Be patient with it.

That gives you something fairly strong. Drink it over ice as it is, or cut it with water or milk until it tastes right to you. Some people make a much stronger concentrate (around 1:4 or 1:5) and dilute it a lot more later, which saves fridge space. Both work, it’s really just a matter of taste and how big your fridge is.

And yes, this is the one time I’m happy for coffee to live in your fridge. If you read my post about why beans don’t belong in there, brewed coffee is a different story 😉 Most guides say it keeps for about a week. I’d try finish it within a few days though, because it does seem to go a bit dull the longer it sits.

Flash brew, if you’ve already got a V60

If you’ve already got a V60 (and if you’ve read my V60 post you’ll know how long it took me to buy my own), you’ve got everything you need. A decent place to start:

• 20 g of coffee, ground a touch finer than you’d normally go for a V60. You’re using less hot water than usual, so you want it to extract a bit more efficiently.
• 120 g of ice in the jug or carafe, under the dripper.
• 180 g of hot water (just off the boil) poured the way you normally would: a small bloom, wait 30 to 45 seconds, then the rest in two or three pours.
• When it’s all through, give it a good swirl so the ice melts in properly, then pour it over fresh ice in a glass.

That’s 300 g of total water to 20 g of coffee (1:15), with 60% of it hot and 40% as ice. Plenty of people mess around with that split and you’ll see anything from 50/50 to 70/30 online. If it tastes thin and watery, grind finer or add a gram or two of coffee. If it’s harsh or bitter, go a bit coarser. Basically the same adjustments you’d make for a normal hot pour-over.

Which beans go where…

This is where I’d put most of your thinking, because I reckon a lot of disappointing iced coffee comes down to using the wrong beans for the method.

For cold brew, go for coffees that are already chocolatey, nutty and sweet, and not too dependent on bright acidity to be interesting. Medium roasts and blends tend to do really well here, and they’re even better if you drink it with milk. Something from our blends is a good place to start.

For flash brew, this is where the lighter, fruitier stuff gets to show off. Anything on our single origin page with fruit or florals in the tasting notes is worth trying this way (and if you’re not totally sure what those notes mean, my tasting notes post explains them, minus the nonsense). Making a really expensive, delicate coffee into cold brew isn’t a crime or anything, but it’s a bit like buying a nice bottle of wine to make sangria.

So if you’ve tried cold brew before and thought “is that it?”, it could well have been the beans, some just aren’t suited to it. And if your only experience of iced coffee is a hot coffee that got left in the fridge overnight… please, for the love of God, try a flash brew once. It really is a completely different drink, and it takes about four minutes.

For a proper visual walkthrough of both, James Hoffmann’s YouTube channel has covered iced coffee a few times over the years and is (as always) a good rabbit hole for a hot afternoon.

Anyway, I’m off to check whether the southeaster is planning to calm down before Sunday. If you make either of these, tag us on Instagram at @apothecary_coffee_co. I’d love to see what you end up with, and which side of the cold brew vs flash brew argument you land on.