How do you make the perfect cup of coffee?
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7 February
10:39
12 February
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Hopefully, there’s no such thing as the perfect cup of coffee. Instead there’s the cup of coffee that’s perfect at a certain moment, usually in the context of time or place. That could be the 11am takeout that gets you away from your desk, or an espresso in a classic Italian bar.

We are now seeing the first coffee making robots, which I’m sure will make great technical coffee, but to me that's missing the point. People go into a coffee shop for the environment and the interaction, even if it’s a place to go to catch up on emails or phone calls.

Having said that, there are several rules that everyone can apply when making a cup of coffee, whatever method you use – pressurised (the espresso machine), the aeropress, French press or drip, such as a Chemex, plus all the other weird methods offered on Kickstarter.

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Firstly, you should always clean your coffee making equipment. Coffee is chemically active and anything it touches has a tendency to pick up an oxidised, rancid flavour. Without regular cleaning, you’ll detect a smell that’s at best burnt, or worse rancid. The only solution to that is a dedicated cleaning product such as Puly Caff or Joe Glo. Every home user will benefit from using a proper cleaner.

Freshly roasted coffee has delicious flavour that significantly declines a month or so from roasting, so always check the roast date on your coffee. If there isn’t one, that’s a pretty certain sign that the coffee is old and stale already. Roast level is very contentious and culturally rooted. I like lighter, more fruity roasts, other people like darker, more bittersweet flavour profiles. That’s fine, so experiment until you find one you like.

The mineral content of the water you use has a big effect, a Brita filter is a good start, but if you really want to see the difference, use bottled water like Aqua Panna, or Waitrose Essential, which is very cheap.

"Freshly roasted coffee has delicious flavour that significantly declines a month or so from roasting, so always check the roast date on your coffee." 

Water temperature is also important. Aim to heat the water to around 92 to 97 degrees. Above 97, you will over extract bitter compounds, creating a flat and bitter taste. The fruity and acidic notes will also diminish – you’ll end up with something tasting like a cup of cheap coffee even if you’ve actually spent money on decent beans. To ensure the right temperature, boil the kettle and leave it to stand for a minute or two, or turn the kettle off just before it boils. If the water is too cool, it will under extract and deliver a flat, boring, sour cup.

When it comes to specific methods, here are some widely-accepted techniques for optimizing your brew:

THE ESPRESSO MACHINE

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This is a highly pressurised method, which makes it very sensitive to grind size. Only a well-made burr grinder will give you an accurate particle size and distribution. In fact, I always say it’s reasonable to allocate as much money for the coffee grinder as the actual espresso machine. There are no shortcuts here, a good grinder will be expensive for the home user, which is one of the reasons I go out for espresso and make filter at home. If you do want a good home espresso set up at a reasonable price, have a look at the Rancilio Rocky, Compak K3 or the Sage Smart Grinder.

Why the investment? Because the grinder needs to deliver a consistent particle size. Size dictates the speed the water runs through the coffee bed in your portafilter. If the grind is too coarse, water will run through too quickly - it won’t have time to pick up all the flavours. Too slowly and the coffee will be over extracted, causing it to taste bitter.

Commercially, we use brew recipes, which indicate a ratio of ground coffee in, relative to liquid espresso out. Sixteen gram of ground coffee in to 34 grams of espresso out in 25-28 seconds would be typical. Scales that measure in 0.1g increments are very cheap and useful for achieving this. (And are available on Amazon or Ebay). Experiment with grind size changes - smaller to increase the extraction time, larger to decrease. Keep your dose consistent.

"Tamping is misunderstood - it does almost nothing to control shot time because the brew water pushes much harder than you can tamp." 

Once you’ve established your grind size, you’re good to make shots. After you grind, make sure to distribute the coffee evenly in the portafilter basket. You can use your fingers for this, or one of the various distribution tools on the market. Then tamp the coffee down - you don’t have to gorilla it.

Tamping is misunderstood - it does almost nothing to control shot time because the brew water pushes much harder than you can tamp. Instead, it forces the brew water to spread over the coffee bed, which gives a more gentle pressure and helps to prevent channeling (where the water finds the path of least resistance in the bed and passes unevenly through the ground coffee).

You should expect to wait for around three to 10 seconds before any coffee emerges. If it comes through straight away, the grind is too coarse. If it’s not coming through after 10 seconds, the grind is too fine.

We know that coffee contains a variety of soluble compounds, including acids, salts, sugars, bitters, and roasting compounds. The way the water percolates through the coffee bed determines how much, and at what ratio, we extract those flavours. A tasty balanced espresso combines all of those flavours. An imbalance in any of those flavours and the espresso will taste unpleasant. But following these simple guidelines should ensure you get a great drink.

THE FRENCH PRESS

This is what experts refer to as a “complete infusion method” – the coffee and water are mixed together and the water does not flow through the coffee, instead it infuses with it. The upside of this is that you get a very even extraction - all the coffee gets pretty equally wetted and extracted. The downside is that you often get an overall under extraction (incomplete flavour) and residual fines passing through the coarse filter.

The internationally recognised coffee-to-water ratio is sixty grams of water per litre, which is a good guideline to work from. Pour your ground coffee into your pre heated French Press.

Once you’ve got your water to the right temperature, pour it quickly over the coffee. You’re trying to get a bit of turbulence in the brewer so the coffee and water are well mixed. You can either pre-measure your brew water, or pour with the whole French Press on a scale to get an accurate water measure.

Leave the coffee to sit for four minutes. You should see a layer of coffee floating on top of the brew. This is known as the crust and giving it a quick stir with a spoon will cause it to sink to the bottom of the brewer. Wait three to four minutes after breaking the crust. This will stop the brewing process and allow the plunger to push down more easily. Your coffee will still be hot.

"Once you’ve got your water to the right temperature, pour it quickly over the coffee. You’re trying to get a bit of turbulence in the brewer so the coffee and water are well mixed."

This trick also prevents an overly sludgy drink, though you should expect a little sediment. The French Press has very wide filter holes in the mesh; a lot of fines pass through, but French Press drinkers argue that the fine particles contribute to the body of the coffee.

DRIP METHOD

This method uses percolation, which means that water is poured onto the top of a coffee bed, and passes through it. Usually we put the ground coffee in a paper filter, although you can get ceramic or gold if you want. Paper does everything you want though, and it’s cheap and compostable. It’s a really good way to get a complete brew because saturated water is constantly replaced by unsaturated water, giving great extraction dynamics. It also delivers a clean cup, with no sludge because of the fineness of the paper filter.

First of all, pour hot water through your filter paper into the sink or your cup, which will help to reduce any papery taste and pre heat your brewer. If brewed coffee hits a cold mug that’s fine, but if hot water hits a cold brewer it will affect extraction quite noticeably.

Pour your ground coffee into the paper – stick to the same coffee-to-water ratio as for the French Press. There should be a lot of gas in your coffee, which is a sign of freshness. The gas is carbon dioxide, created naturally by the roasting process, but it can interfere with the flow of water and the extraction of flavour. As you pour on hot water, gas bubbles visibly come out of the coffee. This creates a physical barrier that prevents water from getting into the coffee particles and extracting properly. A simple trick is to pour one third of your brew water onto the coffee first, give it a quick stir to release the gas, and then pour on the rest, making sure to evenly wet all the grinds. If you see coffee up the side of the filter, "high and dry”, it’s not being extracted evenly.

"If brewed coffee hits a cold mug that’s fine, but if hot water hits a cold brewer it will affect extraction quite noticeably."

Aim for a contact time of two to three minutes with drip methods. Longer brew times will usually produce bitterness. If you detect bitterness, grind coarser next time. If you find the brew bland or lacking finish, grind a bit finer. Making coffee is always a balancing act: I go finer and finer with my grind until I taste bitterness, then back off a bit.

Now you’re ready to drink. It’s best if you don’t re-heat coffee, even though many people like their coffee hot. Unfortunately, many of the popular flavours in coffee can be highly volatile - they evaporate or degrade easily, meaning that some of the interesting high notes and delicate flavours are lost if you hold it for more than 30 minutes, or reheat.

Regardless of method, you will find that hot coffee tastes of... hot coffee. People are often surprised by how much more complexity you can detect in cooler coffee, so give that a try – 40 degree centigrade coffee tastes great.

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