Contact for Content - Exploring Time During Espresso Extraction

Posted by Matthew Patrick McLauchlan on

In this blog post I’ll be exploring the time component of an espresso recipe and exposing why it should be the most flexible part of your recipe when it comes to troubleshooting.

When we measure the duration of our extractions, what does this measurement actually indicate? This question frequently comes up, in one form or another, during our classes at the Academies. Extraction time is a rough indicator of the total amount of content being removed from espresso, but it doesn’t exist in a void and it’s important to understand the other factors interacting with this variable.

This becomes apparent while working with the same roast batch of coffee from one week to the next. Here’s an example of what typically happens if you use a static time target for your recipe:

Example


1-7 days 7-14 days 14-21 days
28 seconds 28 seconds 28 seconds
Lower extraction yield Average extraction yield Higher extraction yield
17.8% EY 18.5% EY 19.2% EY


A 28 second extraction might taste under-extracted in days 1-7 after roasting, amazing from days 7-14 after roasting, and increasingly over-extracted from days 14-21 and onwards.

What gives?
The problem lies in that the influence of a static extraction time will be defined by the flow rate (how quickly the water is flowing during that time). Flow rate, in turn, is determined by several factors that may change and interact in different ways over the lifespan of roasted coffee:

  • Gas content (CO2)
  • Grind particle range
  • The pressure profile of the espresso machine
  • Dosage in the basket
  • Distribution of coffee in the basket

If we add those elements to the table above, it should provide a snapshot of why flow rate changes occur:


  1-7 days 7-14 days 14-21 days
Extraction time 28 seconds 28 seconds 28 seconds
CO2 Highest Medium Low
Moisture Highest Medium Low
Extraction result Under extraction Good extraction Over extraction
Grind Most coarse Optimal Finer
Pressure 9 bar 9 bar 9 bar
Extraction yield % Lowest Optimal Highest
Taste results Under extracted Optimal Over extracted


As outlined above, CO2 levels and absorbency of coffee particles help to create differing levels of resistance for our brew water travelling through. Only by aging your coffee can a more static time be used to achieve optimal results. However, for times when coffee isn’t optimally aged, it’s wise to adjust your extraction time accordingly.

Quality
Assuming a consistent brew temp and pressure for now, two of the most important brew parameters to maintain in order to achieve a repeatable extraction yield are brew ratio (dose vs beverage weight) and the size of your ground particles.

Changing the size of ground coffee particles is the principal way baristas will alter their flow rate in order to achieve a consistent extraction time. Unfortunately, if we lock time down as a static variable, our grind has to change quite significantly from a coarse grind while the coffee’s fresh to a much finer position as it ages and loses its natural resistance.

Here’s the testing we’ve done to show this effect.


9 Days old - coarser grind

Dose Beverage Time TDS Yield %
20.00 38.91 26.63 9.38 18.91

16 Days old - finer grind

Dose Beverage Time TDS Yield %
20.00 39.04 26.88 9.55 19.30


These are the average numbers resulting from a batch size of 8 samples per test. As you can see, the brew parameters here are super consistent (just over 0.1 gr for beverage weight, 0.2 of a second, and exactly 20gr dose), but the TDS % and extraction yield % are significantly higher across roast dates.

These results are from the same coffee, from the same roast date and batch, prepared over a two week period, with the time static for both recipes. So when keeping the recipe exactly the same but altering our grind, we receive different extraction yields and different cup results.

As we altered the grind setting to be finer in order to keep the time in a static position, we have allowed more content to be dissolved, resulting in a higher extraction yield (and a potentially tastier extraction too). By keeping the grind in the same range but allowing for a lower time target, we could achieve a more consistent extraction yield.

Use time to achieve consistency of quality
When managing the quality of espresso, it’s wise to use an espresso recipe in conjunction with tasting (hopefully there are no surprises there!). A refractometer is a very handy tool if you can get one. A recipe is a great starting point for any coffee but, as outlined above, you’ll need to adjust the recipe somewhat if your coffee isn’t optimally aged or providing the results you expect.

After adjusting your grind to achieve a recipe, taste and/or measure the extraction yield. If you believe your espresso tastes over-extracted, you’ll need to adjust the time target to a lower number and vice versa.

Quick Tip: When changing your grind coarser to achieve a lower time target or finer for a higher target, if you’re using a Mazzer Robur, an adjustment of 1 notch on the grind collar will alter the time by 3-4 seconds. To tweak your espresso extractions, move by ½ notch increments (2 seconds at a time) and taste as you go. (Note: these rules of thumb will depend on a number of factors including the wear on your burrs — pay attention to the time impacts of your adjustments and you’ll soon learn the ins and outs for your specific grinder.)

This creates a standardised approach to dialling in any coffee, no matter what origin, roast development, density etc. There’s a time in that range when you’ll be extracting optimally and we want to hunt that time down and stick to it.

Here’s how this looks in practice:


Starting point

Dose Beverage Time
20g 40g 28s
Coffee age Tastes Adjustment
27 days overall good.
Slightly underextracted/sour,
lacks body and sweetness.
1/2 notch finer

New recipe

Dose Beverage Time
20g 40g 30s
Coffee age Tastes Adjustment
27 days balanced, sweet, great Just don't


By the above example, 30 seconds appears to be a better extraction time for this coffee. Is this therefore the time which will always deliver that amazing spro? Not likely.

However, with the process and context we’ve discussed above, you should be able to tweak your recipe to hone in on the delicious zone for any coffee — remember, learn the rules and use your sense of taste to know when to break them!

This article was originally published on the Five Senses Coffee website: Contact for content – Exploring Time During Espresso Extraction.

Cafe Operations CMCR Espresso Making Five Senses

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