Defining Espresso Brewing Recipes

Posted:  July 11th, 2011 by:  wolfram comments:  1

I was looking for a way to communicate my espresso brewing recipes to the consumer. In the past I was using simple information, consisting of the dose and the brewing temperature only. But the given information is of no use at all. Why? Some people are already confused by this “depth” of information, they just don’t know what to do with it. They don’t understand brewing as a process whose parameters can be controlled to produce a predictable result: “one day the coffee is good, the other it is not, this is how it is”.

On the other hand the information I have given so far just isn’t enough to allow to reproduce what I had in mind, so I decided to add more detail to it. Nevertheless, a litle knowledge may be required to understand my thoughts at the end, so we will go into espresso extraction in the beginning. The following parameters come into play if we are talking extraction:

  • grind size
  • dose
  • contact and brewing time
  • temperature
  • pressure

All of the parameters listed above influence one another. So just changing one will result in the need to adjust another one. Undrestanding the corresponding correlation is the key knowledge of a barista.

The grind size is important to control the overall surface of the coffee being extracted. By adjusting the surface you change the capability of dissolving content from the coffee bean into the brewing water. The larger the surface (and thus the finer the grind) the faster a wide range of substances can be dissolved. Having a large total surface is neither good nor bad, since it depends on the coffee used and – as already stated above – in the interaction with the other parameters. But one thing should become clear: creating uniform particles (in general) and a subset of fines is essential, thus grinders capable of doing this (fast and without heating the grounds) can get expensive.

The dose is the total amount of coffee being used for brewing. Again, more coffee means that you have the capability to extract more content in total. A coffee bean consists of 70% of fibre and only 30% of substances that can be dissolved into the coffee. Grinding finer and finer thus doesn’t necessarily mean that more content can be extracted (as well as getting higher in temperature or increasing contact time). There is a maximum of (around) 30% of content that can be taken out of the bean and there is nothing beyond. To make it a litle more complicated the best results are usually shown if a range of 18% to 22% of the content of the bean is dissolved. If lower than 18% of the content is extracted (we are talking about under extraction) the brew might be strong but lacking balance and delicate and more refined aromas are not allowed to shine through (terroir of the coffee). Extracting above the 22% (over extraction) usually results in a weaker brew that tends to be a litle dull. The 18% to 22% range has been defined in the brewing standards of the SCAE and SCAA.

The contact and brewing times are two separate aspects to cover. The brewing time is the more obvious one: it is the total time the pump is running and water is flowing through our coffee bed. In the past brewing time has been considered being a standard (say 25 seconds), nevertheless, this is outdated today. Why? Usually standards (like 7g dose per shot, 18 to 25 seconds brewing time giving 25 ml of espresso) are defined based on the best definition that is possible to date. While dose is still a vital part of the definition the others aren’t any more and are replaced by extraction ratio (based on the weight of the grounds, the weight of the shot produced and the TDS of the brew). The reason is, that we are able to measure these aspects today and that this has become a quite usual tool in the speciality coffee industry (finding accuracy weights in a coffee shop thus is always a good sign). The brewing time usually reflects (roughly) the total amount of liquid that can be produced, again this is neither good or bad. The more important thing is contanct time which is the time of the water actually being in contact with the coffee. As you might guess, this depends on the dose, the grind and the pressure of the water (and not that obvious, on the temperature as well). Since dissolving solids from coffee into water takes time, increasing the contact time (giving more time to dissolve the solids) also increases the chance that more content ends in the brew.

Brewing coffee is a chemical reaction and as we all (might) still remember from the basic chemistry classes in school, chemical reactions can be influenced by temperature. Increasing the temperature speeds up a chemical reaction while decreasing it slows it down. In addition temperature can be used to control how we perceive acidity and other aspects of the brew. The colder the brew the more acidity is perceived, on the opposite astringency might rise. Higher temperature do the opposite, dimish acidity bringing out the sweetness. Aromas are perceived different depending on the serving temperature as well. Again things are not as simple as they sound. Increasing the temperature might result in dissolving more acidic content from the bean than the effect of dimishing its perception might be. The rule of thumb thus might not work out quite well in any situation. Nevertheless, being in control of the brewing temperature has become an important aspect of espresso brewing (0,5°C steps can be perceived easily).

Finally there is the brewing pressure. Again in the past it has been defined as a standard – 9 bar of pressure – which tends to be the pressure used commonly everywhere. Nevertheless, due to new machines like the La Marzocco Strada, which allows for a dynamic pressure control, this stronghold may come down also. We didn’t have the time to play around for long enough on Tom’s Strada to really give a well founded opinion on this but first tests showed that you can brew outstanding shots way outside of the pressure range of 9 bar.

After going through all of the information above the thing to finally mention is extraction ratio. The extration ratio defines the amount of solids dissolved from the bean into the brew. To be able to calculate this value one needs three things.

  • weight of the dose (dose)
  • weight of the shot (beverage)
  • measurement of the total dissolved solids (tds)

Weights (of course) are measured using accuracy scales while tds can be measured by a refractometer like Extract Mojo from VST. The calculation of the extraction yield goes like this, if you end up with a value around 18 to 22 you are in good company.

extraction yield = beverage / dose * tds

As I mentioned in the introduction, the thing I want to talk about is the capability of defining how I brew a shot (of a certain coffee) so this can be repeated by others more easily and helps to find a direction. The key of being able to define this is standardizing the aspects of brewing. Defining the extraction yield, combined with dose, drink weight and brew temperature is quite helpfull in the beginning but turned out to be unsufficient to reproduce the exact same results. So how do we go from here?

La Marzocco and VST developed a new gadget, the VST filters. This article is not VST basket specific, I will cover this topic in a separate post after doing some final experiments. Nevertheless, to me these filters provide three major advantages above other filters around.

  • They are manufactured in a way that allows for a consistens shot, from basket to basket. The default baskets provided with espresso machines usually vary widely in quality and rarely are two baskets identical in flow rate and other aspects. Having consistent baskets that are 99.9x% identical to another one helps comparing the findings and producing uniform shots.
  • The baskets are manufactured for different doses. Thus a 15g basket is less deep than a 18g or a 22g basket. Usually baskets are used that can hold too much coffee, compared to the required dose. The result is, since channeling should be avoided for underfilled baskets, that baskets are filled up to the top to get a stable coffee cake. Most of the time this results in grinding coarser to get the required flow rate. The result of those extractions are usually underextracted. Having the proper basket size at hand allows for better dosing control.
  • The baskets provide a more uniform flow rate, due to the precise manufacturing of the holes (compared to the more random hole sizes of ordinary baskets). In addition the holes are covering a larger area of the filter. Many existing baskets do not have holes up to the sides of the basket, resulting in a portion of the coffee cake to be underextracted (the lower ring in the basket).

Beside all the positive effects these baskets have they provide one major thing: they are consistent. Thus one more variable can be removed from the espresso preparation process. In total the following parameters seem to cover the espresso preparation in a way that allows for a more easy reproduction.

  • San Juanillo – Costa Rica, Naranjo
  • extraction yield: 18,1%
  • dose: 18,5g
  • beverage weight: 30 g
  • brew temperature: 96°C
  • brew pressure: 9,2 bar
  • preparation: La Marzocco GB/5, 15g VST filter basket

This information helps to understand the direction into which to head to get what I find interesting in the coffee mentioned.

1 Comment

Posted By: Steffen On: January 15, 2012 At: 12:43 am

Hi Wolfram,

I second the general approach and would annotate that the method of TDS measurement is also to be communicated.

When following the Mojo Guide for Espresso, one would use a syringe to obtain the coffee below the crema and let the solution cool down.

As we both assume the crema as part of the extraction thus count on these solubles as well, we should perhaps make clear that measurements are mostly done with a stirred espresso and with the crema counter to the suggested Mojo method plus their filters.

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