Coffee Brewing Guide - Espresso

Coffee Brewing Guide - Espresso

How to make the perfect espresso at home (or at work).

Brewing guidelines for espresso machines:

   • rotary pump (commercial)
   • vibrating pump (domestic)
   • spring or lever piston (vintage commercial and domestic)

Quick reference instructions:

  1. Ensure your whole machine has reached a stable temperature.
  2. We recommend using a double basket with nominal 18-20g dose (examples include La Marzocco, Bezzera, Synesso and VST).
  3. Start with a brew ratio of about 60% (dry ground coffee to liquid coffee) e.g. a 18g dose extracting a 30g shot in between 'ristretto' and 'normale'.
  4. Grind your coffee into a small container.
  5. Place your ground coffee container on digital scales and tare the scales. Pour 18g of ground coffee into the double basket in the portafilter. The scales should now read (negative) 18g.
  6. Distribute and tamp the coffee. We thoroughly recommend the Weiss Distribution Technique (WDT).
  7. Briefly take your warm espresso cup and place it on the scales and tare.
  8. Lock in the portafilter and brew immediately.
  9. The first drops should take about 5-8 seconds to appear at the spout for traditional portafilters and 2-4 seconds for naked portafilters.
  10. From first drop, you would hope to see 27mL extracted after a further 20 seconds, approximately. Total brew time about 25-30 seconds.
  11. From approximately 20 seconds after first drop, the solubles yield will not increase (extraction is exhausted) and increasing dilution will occur i.e. the additional water is not extracting coffee solids but is flowing into the cup, diluting what is already extracted. Use this knowledge to fine tune the strength of shot (TDS) to suit your taste preference.
  12. Weigh your shot. You're aiming for about 30g net beverage weight. (approximate figures of 11.1% TDS at an extraction yield of around 19.5%).

Fine tuning your brew

"I want a stronger tasting coffee with the same flavours"

  • Stop the shot a few seconds earlier to reduce dilution which occurs from 20 seconds following first drop.

"I want the fruity high notes to be more prominent"

  • Increase the dose by 0.1g and grind a touch more coarsely to maintain constant shot times.

"I want to soften the fruity high notes and make the sweet flavours more prominent"

    • Decrease the dose by 0.1g and grind a touch more finely to maintain constant shot times.

    Recommended baseline grind settings:

    • Fine to very fine.
    • Shot times around 25-30 seconds, with 25 seconds being our preference.
    • To slow the shot use a finer grind and vice versa.
    • Optimum brew ratio for our coffee is in the range 55% to 70% with 60% being our preference.

    Dose levels

    Jim Schulman showed that for a given basket geometry on a given machine, that dose accounted for 75% of the effect on extraction yield; if shots were cut at the onset of blonding and shot times and weights were roughly constant. This effect was attributed to the dose affecting the height of the dry coffee bed and hence affecting the average length of water path - or the hydraulic depth. Why does this matter? Well, it is thought that the deeper bed of coffee exhibits less even percolation throughout the varying depths. Experiments have shown that the water reaching the bottom of the bed is already saturated with soluble coffee and therefore is unable to extract the solubles from the coffee positioned at the bottom of the bed. This mechanism explains the extremely low extraction yields (and dominant acidic flavours) in domestic espresso machines with 50mm, 19g baskets i.e. they are very tall beds of coffee.

    For the above discussion, given the shot times were held roughly constant to fit within normal espresso guidelines, you may have realised that the dose could be argued to be a proxy for changing the grind while maintaining shot times. Thus the low extraction for the higher dose came about due to a coarser grind - the same principle at play in a filter brewing method. The fact is that there are numerous overlapping variables and both these mechanisms contribute. In practice it is not possible to only vary one parameter in isolation but at least if you understand the range of mechanisms at play you can make reasonable efforts control them and vastly improve your brewing consistency and coffee enjoyment.

    Brew Temperature

    If your machine brew temperature is adjustable then you can experiment to suit your preferences. If not, then aim to ensure it is consistent and close to 95°C. You should not see steam coming from the shower screen and if you do it should be only brief while you conduct a pre-brew purge. Purge enough water to dissipate the steam in the brew circuit but also conduct the purge far enough in advance to allow the new water in the brew circuit to heat up to the correct temperature. For machines that are not running too hot in general but need a purge because they have been idle for too long, a purge 1 to 2 minutes prior to brewing is likely to be about right.

    Detailed information on coffee extraction principles: Science of Coffee Brewing

    Tagged : Workshop, How-to, Brewing, Espresso

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