ESPRESSO [THE SCIENCE OF BREWING]

 

You can add hot water to ground coffee and call what comes out a cup of coffee, but I don’t think you should. Making a great (or even servable) cup of coffee involves a lot of science, and the interaction between the coffee and the water can be affected by a lot of tiny variables.

Water temperature is important. Standard industry practice dictates that water temperature should fall between 90-96 degrees. Water that is hotter than this can make your coffee quite bitter, cooler water can under extract the coffee.

The quality of the water is just as important. You’re looking for an acceptable range of calcium hardness, alkalinity, pH, sodium, and total dissolved solids. (Third wave water create capsules with this specific recipe that you add to distilled water). 

The chemical make-up of tap water around the world vary widely, this is why people think bread tastes so great in San Fran, Pizza in NYC and Coffee in Seattle. Sticking with filtered water is usually best, you can even buy specific filters for coffee machines which filter in new compounds and out others. 

How you grind the coffee is the third factor. Burrs make for more evenly formed coffee particles, resulting in a more consistent extraction – if particle sizes aren’t uniform, some will overextract while others will underextract. Overextraction leads to bitter coffee.  Underextraction leads to sour coffee. It’s like putting different sizes of cookies in the oven, some might overcook and other might undercook.

Timing is everything. In pour-over methods, the contact time for water and coffee is controlled by gravity. If the coffee is too coarse, water will flow through too quickly, and the brew will be thin. If it’s too fine, the water will be in contact with the coffee for too long, resulting in a bitter cup.

There is no universally accepted grind size for brewing, it’s all trial and error, taste and go again. This is where ‘Dialling in” comes in.

[PULLING A SHOT]

Starting Points

Espresso extraction involves forcing hot water through a finely ground coffee puck to produce a viscous, intensely flavoured drink. A number of factors influence the taste of the espresso itself, but for the sake of simplicity we’ll assume a few constants: pump pressure at 9 bar, 18 gram VST baskets, and water temperature set to 93 degrees Celsius at the group head. These are what we use and they remain the same for every espresso we brew and produce excellent results on our equipment.

I recommend a 1:2 brew ratio for espresso. (this means for every one gram of coffee you should get double out in espresso)

  • For a double basket: for 18 grams of ground beans in, you want to get about 36 grams of liquid espresso out. If you do not have a scale to weigh your input and output, it translates into 1 oz of liquid, including the crema. 
  • The best shots of espresso are pulled in a range within 28-32 seconds from when then pump starts, with espresso dropping from the portafilter after 5-7 seconds.
  • Grind your coffee fresh and be as efficient as possible. Don’t let ground coffee sit in the portafilter, and don’t let the portafilter sit in the group head loaded with espresso grounds before brewing. Coffee stales very quickly once it’s ground.
  • On another note, always remove the portafilter from the grouphead once done to prevent used coffee staying in the group head and making the next shot bitter. Always clean out the portafilter with a towel to remove further grinds and to ensure its dry.
  1. The Grind

    The basic premise of dialing in your grinder is to ensure that your 1:2 brew ratio occurs within 25-30 seconds after your pump starts. This is a vitally important skill for any barista. Start with a fine grind – coarser than flour, finer than table salt. Follow the instructions below and we will circle back to dialing in your grinder.

    1. Dose

    I recommend a dose of 18 grams of coffee when using a double basket (typically found in a double spouted portafilter - if you're confused by all this "double"). Weigh all your shots before you pull them to make sure they’re accurate.

    1. Level And Distribute

    The reason I level the coffee bed is to ensure that the water does not flow out faster in any area. This is called channelling and can lead to an under-extracted shot of espresso. I recommend gently tapping the side of the portafilter with your hand to more evenly distribute the grounds. You can also settle the grounds by tapping the portafilter on a tamping mat. Having a grippy surface is also helpful for stable tamping.

    1. Tamp

    Grip the tamper handle as though you were grasping a doorknob. Keep the tamp surface in line with your wrist and elbow and tamp straight down, leaning your weight into it comfortably. The amount of pressure is not nearly as important as your consistency and ability to keep the tamp perfectly level so water doesn’t find weak spots. I would always recommend tamping as hard as you possibly can, the margin of error is much less if you do so, if doing a ‘light tamp’ the margin of error is much much greater.

    1. Go!

    Clear any ground coffee from the rim of the portafilter. If your machine doesn’t have an integrated shot timer, now is the time to set your phone to timer function. Flush water through the group head for 2-3 seconds prior to inserting the portafilter. Engage the portafilter in the group head and immediately start brewing. Once you hear the pump, start the timer. Stop your shot when you have extracted 36g of liquid espresso.

     

    [Dialing in your shots and grinder]

     

    Don’t panic. There is a 0% chance this is perfect the first time.

     

    PROBLEM

    REMEDY

    30g of liquid came out before 25 seconds (Too fast)

    Make the grind finer

    30g took more than 30 seconds (Too slow)

    Make the grind coarser

    Espresso pulls in target times but tastes harsh

    Make the grind coarser and increase the dose

     

    Dialing in gets substantially easier with a scale. Weighing the input and the output will get you to a great shot way faster than judging liquid volume because the crema will change with different roast types and depends on the freshness of your beans. If you don’t have one, there are terrific inexpensive options. Anything is better than nothing.

    Nailing the perfect recipe for any given coffee can take time and a lot of practice. We always recommend asking your local barista or roaster what recipe they use to pull shots with a coffee. Even more so we recommend experimenting. Try pulling a shot at 40 seconds, maybe one at 20. There are only guidelines in coffee, no hard and fast rules, so you'll often find that your favourite shot exists outside the bounds of the industry standard. What matters most is taste. All of these procedures and measurements are simply in the service of great tasting espresso so, more than anything, trust your palate.

    And always TASTE TASTE TASTE. Remember our old friends under and over extracted?

    Espresso is a complicated beverage, and there is no one solution that provides the perfect outcome. The machine, the mineral content of the water used, and the grinder all influence its taste, and what works in one environment may not translate well to another. However, if you keep in mind the trio of balance, complexity, and sweetness when dialling in, you shouldn’t go too wrong

    [Under-extracted Coffee]

    Under-extraction occurs when you haven’t taken enough flavour out of the coffee grinds. There’s still a lot left behind that could balance out the following undesirables.

    Cast your mind to a shot of espresso that was far too short; a ristretto of a typical Specialty espresso roast. It’s sour, lacking sweetness, weirdly salty and has a disappointingly quick finish. These four things are the most obvious indicators of under-extraction. Let’s go through them in a little more detail.

    Sourness –
    This is a tricky one, especially with our desire for acidity in coffee. I hear lots of people ask “Aren’t sourness and acidity the same thing?” and it’s a very valid question; in a lot of languages ‘sourness’ is the same word as ‘acidity’. As you can imagine, this makes multilingual cuppings a little difficult.

    To clear this up, I always define sourness as being negative. A sour flavour hits you quickly and aggressively. It creates an immediate physiological reaction, you might pucker your lips or it might feel electric or sharp on the sides of the tongue. Sourness is undesirable and distracting. 

    Whenever I talk about acidity it can be either good or bad. It’s more of a category of flavour than a positive or negative attribute. Example: “That coffee’s acidity is delightful” or “That coffee’s acidity is very sour” are both logical to me. Acidity is the umbrella under which lies all sour/juicy/bright/tart things. I could write volumes about acidity, but this week is all about extraction. Back to it.

    Lacking Sweetness –

    In my opinion, the most important aspect to a coffee’s flavour is its sweetness. Sweetness is the best. Have you ever heard someone say ‘this espresso is too sweet!’? Think about that for a second. I strongly believe that we should always be chasing sweetness. It’s my holy grail: something that’s really difficult to find and stupendously rewarding once you get it. Under-extraction isn’t sweet. It’s far from it. It almost always displays an emptiness that leaves you with an unsatisfying ‘I-want-more’ feeling after drinking. The good thing about this lack of sweetness is that it also accentuates the sourness, making under-extraction much more obvious.

    Salty –

    Not everyone agrees with me here, but I’ll argue til I’m red in the face that under-extracted coffee is salty. It’s not quite ‘sorry I added table salt’ salty, but under-extracted coffee almost always has the mouthfeel and/or taste of saltiness. From a tactile point of view, it’s kind of similar to the slipperiness you get from alkalinity (Don’t go and drink ammonia to learn this one. Just trust me).

    Acids and Salts are more soluble than Sugars. This is why an under-extracted coffee is sour and salty – the sugars haven’t had enough time or chances to dissolve completely just yet.

    Quick Finish –

    A well extracted coffee has a finish that lingers for minutes (or hours if you’re lucky). This finish can feel as though someone has left dark brown sugar on your tongue, or as though you’ve just finished a toffee. Yum!

    An under-extracted coffee doesn’t have this finish. Once you swallow, it disappears straight away. You’re not left with any pleasant lingering sensation. It’s an abrupt and unsatisfying end to your coffee experience. Less Yum.

    There are other flavours that indicate under-extraction, but these four are certainly the most obvious. Whenever you taste them, be sure that some part of your coffee is under-extracted!

    Let’s now cast our attention to the opposite end of Extraction Street.


    [Over-extracted Coffee]

    Over-extraction occurs when you take too much of the soluble flavours out of the coffee. This level of extraction results in unfavourable flavours.

    Cast your mind now to an espresso of a typical specialty espresso roast that brewed for 40-50 seconds. Don’t pretend like you didn’t taste it when this happened once. It’s bitter, drying and hollow. These three things are the most obvious indicators of over-extraction. Let’s shine some light on them as well.

    Bitter –
    We’ve all been here. Coffee is bitter. Over-extracted coffee is really bitter. Unless I’m drinking Campari, I don’t want that much bitterness. A lot of this bitterness comes from caffeine, but there’s many other chemicals in coffee that contribute. A darker style roast that has achieved dry distillation will have many more of these bitter chemicals.

    There are thousands of chemicals (pretty much all poisonous) that trigger the exact same bitter signal from our taste buds. This is our body’s way of saying ‘don’t eat that’.

    Drying –
    Dryness in coffee is so incredibly bad because it’s such a strong sensation, and it can last a long time. This sensation is called astringency and is the same as you get from unsweetened black tea, young red wine or white wines with extended barrel time. In wine, this effect is caused by polyphenols: chemicals that are readily found in plants, seeds, bark etc. These are arguably the same chemicals that cause dryness in coffee.

    Polyphenols are bitter and bind to your saliva’s proteins. In layman’s terms, they de-lubricate your tongue, creating a sandpapery or dry sensation in the mouth (This shouldn’t be confused with the wine versions of ‘crisp’ and ‘dry’ – these are terms that denote bright acidity or low sweetness; not necessarily mouthfeel).

    Hollow and Empty –

    This is a personal descriptor I like to use for over-extraction. The coffee just feels empty and lifeless, like you’ve extracted the living daylights out of it and killed everything in the process.

    Well extracted coffee fills your mouth with richness. It’s luscious, smooth and, well, mouthfilling. Over-extracted coffee is empty, hollow, rough and just plain-old yucky. It’s this lack of flavour and character (rather than the presence of a particular flavour) that leads me to use the word ‘hollow’.

    Those are the key over-extracted flavours. Of course there are more, but these are super simple to identify, and should have you identifying over-extraction in no time. 

    The most important thing to note about all of these flavours is that they are generic. You can get them from the most expensive Gesha in the world, and you can get them from sub-commodity grade rubbish. These flavours aren’t desirable. Most of us here are in Specialty Coffee, which means we’re trying to create a product special enough for the customer to want to pay more for it. Extraction-related faults are anything but special.

    Now for the sweet spot, the yum-zone, the goods.


    [Ideally Extracted Coffee]

    A well extracted coffee is a little miracle. A lot of work has gone into balancing countless variables to produce a tiny cup of deliciousness, and it’s imperative to know what this tastes like.

    Cast your mind to the best damn cup of coffee you’ve ever had. It’s sweet and ripe! There’s a clarity to the flavour, like it’s transparent. The acidity is balanced and positive, perhaps complex if you’re lucky. And the finish goes for ever. This is the jam, and you want to know more about it. 

    Sweet and Ripe –

    As I said, the Holy Grail. I’ve spent countless hours teasing more ripeness out of coffees. It never gets old.

    Think of a plum or similar stonefruit as it ripens. At first there’s a lot of acidity and tartness, then it gradually gets sweeter. The sugars are developing and becoming richer, heavier, more cloying. Then it hits a point where just holding the fruit near your nose enables you to smell the sweetness. Right there. That’s the sweetness and ripeness you want from coffee. If you’ve never had that, you’re in for a treat one day soon!

    Clarity and Transparency –

    George Howell has a way with words. He describes the processing method of coffee as being ‘the window through which you see the coffee’. I like to extend this analogy by thinking of the extraction (and roasting) as another pane in that window. If you have over or under-extraction muddying up your glass, it’s harder for you to ‘see’ what the coffee really tastes like. Generic extraction faults are distracting and can impair the provenance of the coffee you’re serving.

    Acidity –
    Fine, complex and definable acidity is truly something to behold in coffee. Acidity is something that’s incredibly beguiling, but also frustratingly flighty. When you get acidity that reminds you of a specific fruit, or even a wine, you’re in the green. If that acidity is so definable and intense that you can pinpoint a variety of fruit and remember the last time you ate it, you’re nailing it.

    Finish for Days –

    This is self-explanatory. A good finish goes nearly forever. A sure sign of good extraction.

     

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