undissolved solids

Cold brew and Iced batch are NOT the same thing and taste different. There are better ways to make them that also don’t include waiting 16h for coffee.

Cold brew (as implied by its name) is [usually] made with course-ground coffee seeped in water at room/fridge temp. Another way i’ve seen this made is with a cold-drip tower that drips water at x no. of drops per second until the upper water reservoir has fully passed through the tall bed of coffee.

Iced Batch (also implied by its name) can be made in three ways (that i’ve observed)

• medium-course ground coffee brewed with filter machine then placing the carafe in the fridge to be cooled.
• medium-course ground coffee brewed with filter machine BUT liquid is flash chilled through cold plates as it drops into the carafe.
• medium-course ground coffee brewed with filter machine that is flash chilled by a certain percentage of ice (replacing water) in the carafe filled, reducing the water-to-coffee ratio used to initially brew the coffee- essentially diluting & cooling a more concentrated solution to be around the same extraction%.

Let’s discuss how all these different styles of iced-filter vary.

Here are the variables at play:

• Extraction temperature
• Grind size
• Immersion vs percolation

EXTRACTION TEMPERATURE

• Determines the rate that coffee particles are extracted into the water
• Cooler temperatures mean slower extraction
  • thus need MORE time to extract the particles
  • but also means certain particles WON’T be extracted because of the lack of heat
• Hotter temperatures mean higher extraction
  • means it doesn’t require as much time to extract the particles
  • will have a fuller flavour spectrum as all particles are able to be extracted with the heat
  • means some unwanted particles can be extracted
  • also presents the possibility of over-extraction = increased bitterness

GRIND SIZE

• Courser
  • water passes through more easily in percolation method (coffee bed less compact) = faster total extraction time = tends to be lower extraction in percolation methods
  • larger size particles mean solubles have to travel further out of the bean = longer immersion times may be required to extract enough of everything
• Finer
  • leads to more compact bed = water passes slower through the bed (finding the lowest path of resistance) = slower extraction time = higher extraction as a result
  • smaller particles mean solubles travel less distance = extract easier overall = can lead to over- extraction and more bitterness

IMMERSION VS PERCOLATION

Diffusion: another term for osmosis to achieve equilibrium. Low-concentrate water drawing solubles from highly-concentrated coffee.

• Volatile aromatic/acids and caffeine are easier to extract even at lower temperatures
• Bitter/Organic compounds generally slower due to their size

Advection: is the process of running solvent picking up particles from the outside of the soluble (coffee) as it passes through (something like outer erosion of a rock-face next to the ocean vibe)

• immersion uses favours diffusion from soluble coffee particles when mixed with water
  • temperature determines how SLOW/FAST diffusion will occur
• percolation – uses a mix of diffusion and advection
  • temperature determines how fast diffusion occurs
  • water flow and water availability (i.e multiple pours or different volumes) determine how much advection occurs

How does this apply to all these iced-filter methods:

1. Cold Brew (drip tower method)
   

• • Temp: room-temp
  • Grind size: medium-course/course
  • Type: slow percolation
  • Expected result:
    • room-temp extraction allows slightly higher extraction (compared to fridge immersion method)
    • slightly more fruity and overall balanced brew

2. Cold brew (immersion/mizudashi method)

• • Temp: fridge/room-temp
  • Grind size: medium-course/course
  • Type: immersion
  • Expected result:
    • a bit more one/two-dimensional brew
    • depending on time (most places recommend 12h-24h immersions) will just taste super smooth (mostly chocolate-notes) and have minimal acidity due to extracted organic compounds overwhelming the volatile acids
    • brewed in a fridge will taste like: smooth, minimal fruitiness, chocolate-y cold brew
    • brewed at room temp (minimal +20C difference to fridge method) tastes like: more intense brew with more clear acidity structure, more stone-fruit characteristics, still quite chocolate-y

3. Iced Batch (carafe in fridge)

• • Temp: hot, cools in fridge depending on how the coffee is stored (in a thermos will take longer compared to glass bottle)
  • Grind size: medium-course (variable on individual tasting)
  • Type: percolation
  • Expected result:
    • slow cooling in fridge can result in lower volatile aroma kept
    • taste: fruit-ier compared to cold brew, more balanced, can have slightly lower aromatic quality compared to other two methods

4. Iced Batch (flash chilled with plates)

• • Temp: hot, rapidly chilled with no dilution
  • Grind size: medium-course
  • Type: percolation
  • Expected result:
    • more volatile aromatics kept
    • taste: more fruity the #3, increased flavour clarity. can still retain body and be balanced

5. Iced Batch (flash chilled with iced, more concentrated)

• • Temp: hot, rapidly chilled with some dilution occurring
  • Grind size: medium-course (can grind slightly finer to compensate for smaller coffee bed)
  • Type: percolation
  • Expected result:
    • Less water available in the hot extraction = lower organic compounds extracted in relative time = increased perceived acidity (which gets diluted a bit by extra water (ice) in the caraffe.
    • taste: more acid-forward, lower body but even more increased flavour clarity. can be a bit sour for some.

Iced filter can be more fun than the same boring 12-16h cold steep that baristas say “all tastes the same”.

Honestly, flash chill plates are impossible for most people to get their hands on. I’ve only seen SEY coffee do something like this. So try the other methods!

Heres a tester recipe for you guys to start with using method #5 (ice-chill method with a hot batch):

• dose: 65g
• grind size: a bit finer than your usual batch-brew recipe (one full number finer on an EK)
• water-in: 700g
• ice in carafe: 300g
• if you have control over bloom (most machines don’t) → double the time
• end TDS: 1.4-1.5%
• pour over a full glass of ice and enjoy
• what to expect: good body from longer bloom, clearer flavour structure/notes that jump out more. 

Have fun brewing! Thanks for reading.
Jos x