February 18, 2011 Nathan

Five Steps to Better Coffee at home: Step Four – The extraction

You’ve got your coffee ready to go after following steps one, two and three – and now it’s time to complete the science of extracting the coffee flavour and caffeine you’re looking for from your cuppa. Here we’ll provide a few tips on espresso extraction, plunger preparation and a guide to stovetop espresso.

Espresso
Espresso is to coffee what nectar is to fruit juice. It’s thick. It’s undiluted. And it’s the basis of most coffee drinks you’ll buy out and about in Australian cafes.

There are, as in every step of the preparation process, a number of variables to be aware of when it comes to extracting your espresso. Essentially, the temperature of the water, the time taken, and the pressure applied to the coffee are the big three.

Water temperature
One of the biggest (and most common) crimes in coffee preparation is using water that is too hot. A lot of machines will overheat if left on too long. Water will sit in the boiler or thermoblock and heat past 96 degrees (about spot on for espresso). The easiest way to overcome this is to flush hot water from the system before pulling your shot (coffee jargon for pushing the button, espresso machines historically used levers for the process of extracting coffee).

If the water is too cold it won’t cause the coffee oils to separate from the granules, if it’s too hot it’ll get too much oil on the way through. Leaving your coffee bitter. If you like bitter coffee use water that is too hot and extract for too long – it’s all about personal taste.

Shot time
The time taken for a shot is important – if the water is in contact with the coffee for too long it absorbs too much coffee oil and becomes bitter, if the water is in contact with the coffee for too short a time (if the coffee shoots through the coffee quickly) it won’t pick up any of these oils and will taste like brown water.

The Specialty Coffee Association of America, a leading authority, suggests ideal shot times of 20 seconds, the generally accepted principle is that between 20 and 30 seconds is ideal.

Pressure
Until recently playing around with pressure during the shot has been largely impossible (this is changing with the latest and greatest commercial machines). When it comes to home machines it’s a matter of finding a machine that will pump water through your coffee at about 9 bar of pressure (15 bar machines are a little misleading).

Plunger tips

  • Boil water.
  • Grind coffee coarsely use about 8gm per 250mL of water.
  • Pour the boiling water into the plunger to heat it (and put the plunger part in.
  • Let the water cool a couple of degrees.
  • Add the coffee
  • Stir and replace the plunger
  • Plunge after 3-4 mins. Push down firmly but slowly.

Stovetop tips

  • Put in less water than recommended on the box, use more coffee than for machine produced espresso.
  • Tamp the coffee (not too hard).
  • Start with hot/boiling in the chamber (use a kettle first). You’ll need to wear an oven mitt or something as you screw the top on.
  • Put on medium heat, use a pre-heated element.
  • As soon coffee starts flowing remove it from the heat.

This should produce thick and rich stovetop coffee with a layer of crema.

This series covers information I used for a coffee information night I put on at my church (twice) and originally appeared on St. Eutychus.com

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About the Author

Nathan Nathan is a coffee lover, home roaster, amateur barista and coffee tinkerer. He's married, has two kids, one turtle, and for a day job works for Creek Road Presbyterian Church. He previously worked in PR. This blog is his attempt to make coffee tax deductible.

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