The Extraction Process And Getting It Right…
This article aims to please from a novice level – right up to the ‘coffee insane’ (not to be confused with the ‘criminally insane’). It covers core fundamentals as well as more technical aspects and techniques. I hope you get a lot out of it. Cheers.
The basic science of this process within the modern day espresso machine– A compressed contained puck of coffee grinds that has heated water forced down through it under pressure (somewhere between 8.5 and 9.5 bar or 115psi and 130psi). As this heated water travels down through the puck, it progressively dissolves flavour containing solids and oils that leach out underneath, emerging from the base of the container (usually a portafilter) creating a coffee emulsion – or extraction – in your cup below.
With most machines (excluding the automatic ones – which I don’t fancy one bit – but which may suit the common punter just fine), you will have a choice between smaller and larger basket volume sizes – some will have two types of each size of basket (one set being ‘single walled’ and the second set (that you should bin) will be double walled – see further on re the double walled rubbish baskets).
Very basically, the smaller basket will highlight more flavours within a bean whilst the larger basket will be more forgiving and provide a more consistent cup of coffee. Better skill (or more accurately ‘consistency’) is sometimes required for the smaller basket – but the reward of flavour highlights is greater and worth any additional effort. Sometimes, you’ll be better off to nail a routine with the larger basket more easily to get a good quality cup that you can count on. Once this becomes old hat, you might go searching for a bit more out of your bean – at this point, it’s time to master the single basket (a good quality grinder will aid in this transition immensely). Grinder fundamentals will be a subject of a future article….
Just some examples of a single (on the left) and double basket (to the right) below. Note the difference in diameter of the perforated mesh area at the base of each basket (sorry the photos are not the same size) – just imagine they are…. –
Your grind settings for each basket will be different relative to basket design – generally the grind will be slightly more coarse for the smaller basket (this very much depends on the basket design and assumes the smaller basket has tapered walls that go inwards with a smaller diameter screen area at the base when compared with the larger basket). The alternative design for various machines sees the smaller volume baskets having an identical screen diameter to the larger volume baskets (the only difference in these being the depth of the basket). This type of design will see both size baskets share common grind settings.
Beware – less expensive machines will provide ‘double walled’ baskets. These have a mesh pattern of holes on the inside of the basket (looking identical to the superior baskets – but vastly inferior in performance) and a pressed pattern on the outer underside of the basket with one single tiny hole in amongst the outer pattern – or it may be absent the pressed pattern, having the tiny hole only. These are designed to negate the need for correct grind (or at least give you a very wide spectrum of grind settings that will do an average job) with the tiny outlet hole helping to provide the back pressure on the coffee grinds to aid in the extraction. The best you can hope for with this design currently is about ½ the flavour with limited highlights resulting from what essentially becomes an emulsion of water and coffee grinds within the basket during the extraction. These baskets are absolute toilet and should be outlawed… I wish you well if this is the only choice you have. To demonstrate how irrelevant your grind setting is with these double walled baskets (assuming your machine has a brew pressure gauge) – load the empty portafilter and double walled basket into the grouphead (without any coffee grinds in it at all) and turn the machine on. Water will jet out of the single hole at the bottom – and at the same time, you should see some sort of reading on the pressure gauge. Do the same thing with the single walled baskets and the water will just trickle out the bottom as if no basket was there at all.
You see, the simple difference is that the double walled baskets rely on the basket design for back pressure. The single walled baskets rely on correctly ground and compacted coffee for back pressure – thus the reason why you yield soooo much more flavour from the single walled baskets (assuming you get everything else right that is….).
If you are stuck with the double walled baskets as your only option (it was a birthday or Christmas gift from your partner that will be missed if you use it as a boat anchor), consider carefully grinding off the bottom outer layer of the basket with some sand paper, grinder or similar to leave the inner basket with the inner single layer mesh just as the flash ones do (if you do happen to pierce the inner basket while doing this, then the boat anchor plan will apply here)…. Or, just educate your partner on how you really appreciate their thoughtfulness and that one of the diseases you contract from making your own coffees is called ‘upgrade-itis’ and then just get a new machine anyway..…
Next bit….. You need your machine’s brew temperature to be stable before trying to extract a shot of coffee – and it needs to be the correct temperature for the specific bean relative to your taste. Better information relative to this can be found under the ‘importance of brew temperature’ article on this website – but – a basic summary is to get your machine to be more stable during the extraction, let it warm up (times for machines vary greatly). A very very rough warm up for most machines would be about 30 minutes. This allows most things in and around the machine to warm up and settle at a temperature. You should then run a few flushes of hot water through your portafilter (the basket thing that holds the coffee with a handle on it). This portafilter should be lightly locked into the grouphead throughout this warm up process as it helps to hold in and stabilise the heat. As far as the correct temperature setting for your palate’s taste goes – it’ll take some trial and error sunshine, trial and error…. 🙂
After removing the portafilter (once everything is warm and you’re ready to start making your cup of excellence), cool it right down under cold running water (this will keep the coffee grinds cool right up until the extraction – it does make a difference – as if it’s burning hot, it starts to evaporate the light oils / volatile acids containing flavours / tastes) and then dry the exposed portions of the portafiler basket thoroughly (this will help prevent channelling through capillary action during the extraction – water will follow the path of least resistance – especially evident whilst under pressure, bypassing the puck & coming out the bottom with very little flavour).
Assuming this is the start of your day and your last session was the day before, grind a small amount of beans (about half of that you would use for a normal extraction) through your grinder and discard them – this will contain the remnants of the previous coffee session – these older grinds that come out from the chute or doser of your grinder will be stale and taste average if extracted – this is due to the fact that once a coffee bean is ground, the surface area of the grounds is about 1 gazillion times more than the original bean setting (gazillion is a scientific term for a truck load). This allows light oils and volatile acids to immediately start evaporating/degrading – thereby losing significant flavours/tastes right away – this emphasises why you should only ever grind immediately before each and every extraction.
Grind settings for this part of the extraction process are really important and are specific to a particular bean or blend. I need to be careful not to get too side tracked here – but I will regardless – because it’s important.…
Each bean/blend will have a particular grind setting that will allow you to get the most flavour from the grinds during an extraction. The traditional ‘party line’ on how to achieve a consistent extraction is that a puck of coffee, tamped (pushed down on using a tamping device) with a pressure of 30psi (about 2 bar or 200kpa), locked into the grouphead and water run through it at a pressure of between 8.5 to 9.5 bar for a duration of 25 to 30 seconds, yielding a volume of liquid between 25 and 30ml’s (for a single basket) and approximately 45mls (for a double basket)…. blah, blah, blah…. Yes, it is good to have a framework – but people, please – treat it as just that. Your machine may operate differently – so may your grinder. Your tamp device (the bit you push down on the grinds with before the extraction) may be a piece of plastic junk. You might not have a clue what 30psi is in practical terms. The actual difference required between grind settings relative to the water pressure also comes into play…. The list goes on and on – it really does. Please, please – be guided by flavour. This is what it’s all about. If you stray in different ways from this ‘party line’ routine and get a flavour that tastes superb to you – then, are you doing anything ‘wrong’? I’d say not champion.
Anyway – back to getting side tracked…. So, each bean takes a different grind setting to get the best from it. This is because each bean will possess inherent differences from one to the next in 2 relevant ways – oils and freshness (one may be a consequence of the other too). A green bean’s size and contents determine what is available for conversion during the roast. The style, temperature and duration of the roasting process will all have an effect on the resulting roasted bean’s available oils and total dissolvable solids contained therein. Basically – and very generally, the more oils (to a large degree) and the consequent greater dissolvable solids (to a lesser degree) a bean contains, the coarser your grind setting needs to be (as a too fine grind setting would not allow the water to push through the puck).
Some beans have a higher oil level content than others – thus the difference between different bean’s grind setting requirements. As far as freshness goes, quite simply – stale beans contain less oil than when they were fresh. Less oil means less ‘binding’ ability of the puck when compressed. Less ‘binding’ ability means it is less capable of providing sufficient back pressure. The net result of this is that as a bean loses its oils (either directly after roasting due to the bean’s origin/roasting process or as a result of the bean becoming stale), the finer the grind setting required to yield a nice slow drippy, globby extraction….
So, even when you nail the grind setting of a particular bean from the get go – be prepared to modify this grind setting to a slightly finer one as the beans age – to ensure you maintain the maximum flavour yielded from each extraction – otherwise, the old ‘toilet water in the cup’ is what you’ll end up with towards the end of your bag of beans…
Ok, back to the subject – but, just before I do….
I mentioned the yield for a single basket (25 to 30mls) and the yield for a double basket (45mls) for a reason. You see, the label of the second basket as a ‘double’ basket can be quite misleading. Yes, there are basket combinations where the double basket does contain twice the amount of grinds than the single basket does – but, for the most part, the double basket will contain roughly half again of the single basket’s capacity – i.e. single basket 13 grams, double basket 19 grams. As a percentage of yield, the 30ml/45ml ratio fits the basket capacity ratio. Even when a basket capacity ratio of 1:2 exists (i.e. 9 grams / 18 grams) – the yield ratio would be stretched indeed to achieve a comparable ratio – because, the grinds (despite there being more of them) will only yield ‘x’ amount that is sweet. Every ounce of water that goes into your cup needs to be run through the grinds first. Once you go beyond a point, any further water run through the grinds will gradually ‘bitter’ the flavours of the extraction. My advice is that if you want a stronger coffee, use a smaller cup – plain and simple. You can do the sums and create an argument any way you like – get the 1:2 basket ratio with a machine and try it out – be critical as to what you’re tasting in each cup – and you’ll see that what I’ve said has merit. It’s all about quality – not quantity….
Another piece of advice is that you unscrew the double spout pourer off the bottom of your portafilter (assuming it has a double spout) and throw it away – that way, you won’t be tempted to over-extract a single puck of coffee, trying to get enough liquid out to make 2 coffees. A rule – a single basket = 150 – 170ml cup. A ‘double’ basket = 225 – 255ml cup – NOTHING ELSE….. (the only caveat here is that some beans will have a moderately different yield (due to roast and origin) – so these figures may go up or down by about 10% – but not by much more).
A short story on this one – I approached a café to see if they might be interested in trying our beans. Whilst waiting for them (they were still doing service), I observed them doing an extraction for an elderly gentleman’s coffee. The ‘barista’ pressed the largest cup size button over and over again, extracting an entire long black (similar to an Americano) from a single puck. She seemed to suddenly realise I was actually watching what she was doing (she was the owner of the café). She turned around and said “We don’t normally do this, he won’t tell the difference anyway”. I replied “That’s fine. I’ll probably leave you with it as I feel we’re headed in two different directions.” I then walked out with my bag of beans under my arm. That café closed about 5 months later – a lesson for everyone – anyone can tell toilet water from coffee.
I’m just about to get back on subject (I really am). But, just before I do – I mentioned cup sizes. I’d like to expand a little on this point – relative to cup quality. I remember having a conversation with a coffee nut (when I was in my very early stages of the coffee disease) – where it was inferred that the quality of the cup had an effect on taste. I didn’t say anything at the time – but I certainly thought it was a load of rubbish…. I’d lake to say now that I was (wrong is not the word here) ever so slightly misinformed. I have consumed shots (quite a few actually) at other venues (both cafes and customer’s houses) and can say emphatically that a cup’s composition certainly impacts on coffee taste (subjectively of course). Try it yourself – the biggest difference is if you drank from a plastic or very thin glass or porcelain cup when compared with a heavy, thick walled fancy coffee cup. We use 60ml espresso and 165ml tulip Nuova Point cups. Their beautiful looks, their massive weight per cup and the fact that their wall thickness feels like you’re putting your lips over the side of your kitchen benchtop aside – they hold their heat, helping to maintain the coffee’s mouth feel and taste from the first sip – right through to the end of the cup – it really does make a difference – because, after all drinking coffee is an experience to savour.
Another side point (yes, another…) – I mentioned a long black is similar to an Americano – they are essentially the same drink, just a different order of preparation – For the Americano, you do the extraction into the empty cup and add the hot water afterwards. For the long black, you add the hot water to the empty cup and do the extraction on top at the end. The differences are that the Americano mixes the sometimes slightly bitter crema into the drink. The long black looks fancier with the crema still sitting on top of the drink when served (also some people prefer the long black as it can have a bit more bite to start with due to the crema).
Right, I will get back on track now, I vaguely promise (ish)..….
Now, with a correct grind setting, grind the required amount of beans for a single extraction. Once you have put these grinds into your portafilter – refer to your machine’s instruction booklet for advice on their interpretation of the correct dose – or, trial and error will usually work just as well – because different machines have different basket sizings and different protrusion depths of the machine’s shower screen into said baskets, requiring individual relief depths of grinds from the top basket lip…. blah, blah, blah.
Once the correct dose of grinds is in your basket, give the portafiler a slight sideways jiggle to evenly disperse the grinds across your basket (gently settling out the high pile of grinds in the middle that exists each time you pour them in). There are a lot of other techniques for this dispersal – some suggest running a finger across the top to disperse the grinds, ready for tamping. Others require you to bang or tap the portafilter down to settle the grinds. I whole heartedly disagree with both of these methods – both create over compressed areas of the puck’s loose grinds – so that when you tamp the puck down, regions of the puck have comparatively lower densities which can affect the extraction and can lead to channelling (where water breaks its way through the puck by pushing the grinds aside, creating a ‘channel’ through which to run down out of the puck, basically flavourless).
By gently and rapidly jiggling the portafilter sideways, very little downward pressure is placed on the fine grinds resulting in a very even spread of density throughout the basket. I know this is in depth, but everything helps – and this is a simple and convenient step to incorporate with your ‘routine’ that yields better, more consistent results. Unfortunately, this method alone is useless if you possess a grinder that is prone to ‘clumping’ the grinds together. An alternative (and very effective) method that will distribute the grinds evenly when your grinder is a ‘clumper’ is called the ‘Weiss distribution technique’. Basically, you dose your grinds into the portafilter basket (clumps and all), then stir them around vigorously with a straightened out paper clip – breaking up the clumps, distributing the grinds evenly throughout the basket, levelling off the grinds within the basket and avoiding any possibility of ‘over pressure’ regions within the uncompressed grinds – all with about 3 or 4 seconds work – easy peasy.
Next – tamping. There are many discussions that relate to convex, flat and concave shaped bottoms of tamps. Which is best?…. Well, consider this – all standard shower screens that i’ve seen (the bit where water runs out from your machine) are flat. These shower screens are designed to emit water fairly evenly right across their diameter. This being the case, why would you want anything other than a flat surfaced coffee puck to match the flat surfaced, evenly emitting shower screen? Wouldn’t this provide conditions that are most likely to yield consistent even extractions? Wouldn’t concave and convex bottom tamps result in thinner and thicker regions of each respective puck – where some grind regions within the puck would slightly over extract and others slightly under?… This may be a topic that forms a discussion thread….
Regardless, your tamping is important. It needs to be flat, firm and even. You can achieve this by holding your portafilter in your non-preferred hand level on a hard, stable surface that is at about waist height. Hold your tamper firmly in your other hand and tamp directly down onto the puck (make your forearm like an extension of the tamper, holding it as near as vertical as possible). The ‘party line’ or commonly accepted standard is 30psi of pressure pushing down onto the puck. You can very roughly achieve this by leaning approximately ½ of your body weight down your arm during tamping (relates obviously to your body weight – it needs to be somewhere near 50kg’s of pressure to achieve the 30psi region)… Again, consistency is the key – once your routine succeeds, stick to it. After the first tamp, there are loose grinds hanging about. Wipe the outer top facing lip of the basket clean to ensure a good seal within the grouphead. Give the basket a slight quick sideways shake to move the loose grinds away from the perimeter of the basket. Some people will tap the portafilter against something instead of this shake method. There is a slight risk that this may disturb the puck which could lead to channelling during the extraction – whether this is the case or not, there is no need to risk it – as the quick shake works. Now, tamp for the final time, using the same method as the first time round. The only difference is that after you’ve tamped (and whilst still applying pressure), twist the tamper by about 1/8 of a turn to ‘polish’ the grinds. What this basically does is any grinds that are slightly standing up or slightly uneven are forced on their side, laying them down evenly with all the other grinds, creating a more even, better sealing top surface of your puck – also important to help prevent channelling during the extraction.
Now, run a short flush through the group head (without the portafilter in) – then clean the underside of the shower screen (where the water comes out of your machine) with a towelling rag (one with a decent ‘pile’ – this pile helps remove any grinds/muck). Repeat this flushing / cleaning process once more just before you insert the correctly dosed and compacted (tamped) puck of coffee back into the group head for the coffee extraction.
You will know if you have the correct grind setting on your grinder along with how much coffee grinds you dosed into the basket and how hard and evenly you compacted the grinds (yes, all of these individually and combined make a difference) by the way the liquid coffee extraction comes out the bottom of your portafilter and into your cup – it should slowly ooze out like warm honey, dripping at first – then changing into a very slow steady thick stream (disregard this if you have one of those double walled baskets – you get what you deserve for buying a piece of junk – or being too gutless to tell your partner (who bought you the machine) the truth about your depth of passion for coffee).
A quick troubleshoot checklist here – if nothing comes out (assuming your machine isn’t stuffed) – either the grind is too fine, you over-dosed the basket or a combination of these can be to blame. Your tamp pressure should not have an effect here – as the fore mentioned components are responsible for stopping your extraction flow. Make a slight adjustment to either and retry.
If your extraction simply rushes out the bottom of your portafilter – this can be a result of your machine running too high a pressure for your grind setting (if your machine’s brew pressure is adjustable). It is more likely a result of your grind being too coarse for the bean’s oil content and/or freshness, uneven tamping, an internally wet basket inside the portafilter, your machine’s pressure building up too fast (creating channels through the puck from the sudden thrust of pressure), insufficient preinfusion (assuming your machine is adjustable in this regard (it wets the top of the puck gently before ramping up to full pressure to help the top of the puck swell slightly to prevent channelling a touch better)), your machine’s flow rate is too high, you fractured the puck slightly due to reckless handling of the portafilter during your ‘pre-extraction’ routine, you didn’t break the clumps up sufficiently allowing different compaction regions to exist within the puck – even after tamping or you had a bad run at it first time out of the blocks. Get back on your horse and give it another crack champ.
Once all is well and everything is running cherry ripe, with a beautiful globby thick extraction pouring out into your cup below, you should stop this extraction the second it starts to yellow (notice I said ‘starts’ to yellow – once it’s completely yellow (or ‘blonde’ as the industry term goes), it’s bitter and too late – a yellow streak in the brown indicates it is well and truly time to stop the flow). This should yield somewhere close to between 25mls and 30mls of liquid for the small basket and as much as 45mls for the larger basket – as I covered earlier… Now, either drink it like this (commonly accepted as an adult beverage) – or add your preferred amount of textured heated milk (commonly accepted as not an adult beverage – I didn’t say it’s a child’s drink, I just said that it is no longer an adult’s beverage… :-))
The trick is that by the third or fourth shot (assuming your technique is perfect and consistent), everything will have stabilised (temperature, grind freshness, etc) and the shots should be coming out tasting absolutely sensational. What this means is that if you are making coffee for your partner, guests that have come around or the dreaded mother in law – make theirs first… :-).
Trust me – it gets a whole lot easier and more natural with a tiny bit of practice.
(Just for info – if you include any sort of link back to your website without seeking approval, your comment will end up in the spam folder. I’m chasing constructive comments please. Cheers).