Iced Coffee Engineering

Mon, Jun 28, 2021 3-minute read

Over the past week or so it’s been pretty warm here on the Canadian West Coast. That’s led me to want to drink a lot more iced coffee than usual. The downside of this being, of course, that take-out coffee is way more expensive than at-home coffee. So it was time to find a home-grown solution to this problem.

I’ve started to make the majority of my home-based coffee in a french press and that’s done a fine job for me of getting my morning coffee with a minimum amount of hassle and an end product that I really enjoy, thanks in part to James Hoffman’s Ultimate French Press technique. So the obvious question was - how do I get good iced coffee that I enjoy just as much?

After doing some digging around online, it seems like most people are creating a form of coffee concentrate that’s significantly stronger than regular coffee, and serving it over ice which dilutes the hot coffee down to a good strength and a nice chilled temperature. That seemed like a good place to start. One of the variables I will be playing with is the brew water : ice cube ratio. The more water you can use to brew the coffee, the better your extraction and flavour should be. But if you don’t have enough ice, it won’t chill down quickly enough.

My Coffee Goals

  • Iced coffee that I enjoy drinking black
  • Final yield of ~ 1 litre
  • Repeatable process
  • Bonus if it’s make-ahead friendly

The general process I’ve followed is to make a double strength (approx) french press and pour it over ice in a mason jar to get the total volume of water (brew water + ice) to the target of Hoffman’s method. This should give a coffee that has the brightness and acidity levels of a hot-brewed coffee, but be chilled down to iced coffee temperatures pretty much right after it’s been brewed. I also have an ice tray that produces fairly large ice cubes which melt relatively slowly so I should be able to get away with a bit less ice in the long run.

Attempt #1

  • 60g coffee (coarse-medium grind)
  • 550ml brew water
  • 450g ice
  • 9 minute brew time

This first attempt was pretty good for a first try. It was weaker than I would have liked but still tasted good and wasn’t overly bitter. I finished the entire litre quite happily.

Attempt #2

  • 60g coffee (medium grind)
  • 650ml brew water
  • 350g ice
  • 20 minute brew time

This second attempt I made several changes in an effort to get more coffee out of my coffee… funny enough I omited the most obvious step of just adding more coffee. This batch was definitely less diluted than the first, but had a bit more bitterness and harshness that I didn’t love. I attribute some of that to the really long brew time, and possibly the grind, but since my grinder is a bit inconsistent anyway I’ll start by modifying the time.

Attempt #3

  • 70g coffee (medium grind)
  • 750ml brew water
  • 300g ice
  • 15 minute brew time

This finally has the balance I’m looking for. Lots of good coffee flavour and gets down to a drinkable temperature quickly. Because I’m making this the night before in most cases, this recipe more or less goes straight into the fridge once it’s done. If I wanted to have it served immediately I could re-balance 50-100g of ice.