How to make the perfect cup of coffee

From a simple cafetière to an espresso machine, there are many different ways to serve up a cup of joe, but how do we know which is best way to make coffee? We asked coffee expert Mat North, owner of Full Court Press, a speciality coffee shop in UK, and the author of Coffee: A Modern Field Guide, who says that brewing coffee is a science experiment; you just need to know which variables to manipulate.

How can we use science to improve our coffee?

Making coffee is a chemical process. We have our solute, coffee, we have our solvent, water, and we create a solution. Within that, there are a myriad of variables that we can control, but there are four key ones that we really need to get a handle on.

Water is the first. Ninety-eight per cent of every coffee you drink is going to be water: it carries the bulk of the flavour. The process of drawing out chemical compounds, what we call ‘extraction’, is really just osmosis. Positively charged ions from the minerals in the water latch on to negatively charged ions that are the acids and sugars, and physically draw them out.

So, by tuning your mineral content, you can tune what kind of acids and flavour compounds you draw out. My favourite weird acid that you get in coffee is isovaleric acid, which gives the smell and taste of blue cheese or feet.

So what should we do to our water to improve our coffee?

Always filter your water. You can use tap water, but you’ll be fighting a difficult battle, especially in hard water areas.

Water contains an awful lot of calcium carbonate, which mutes acidity. If you have a lot of bicarbonate in there you’re going to bring back any acidity that you extract, and make it taste kind of chalky and flat.

What’s the next important variable?

Then it’s your ratio of coffee to water. The Speciality Coffee Association recommends 60g of dry coffee to a litre of water.

Our reusable capsules can containt 5 - 6g of coffee what means a portion between 70 and 100ml of water.

We use that as a starting point because it gives us a balance between strength and extraction, so you get a brew that’s not too strong, not too weak, not too bitter.

What else is important in brewing coffee?

Grind size is the last important variable. A larger grind size will extract more slowly, so if your brew tastes harsh, bitter and ashy (what’s known as over-extracted), then using a coarser grind size will help rectify that. Likewise, if your coffee tastes overly acidic or sour (what’s known as under-extracted) using a finer grind will help. The goal should always be a balance between acidity, bitterness and natural sweetness.

So what should we do to improve the coffee we make at home?

First of all, fresh beans, which means buying less more often. Even whole beans go stale. Or, if it’s more convenient, freeze your beans. It’s an excellent way of preserving flavours and aromas. You can grind from frozen, too.

Use freshly ground coffee. All of the aromatics and the acid compounds in coffee are volatile, and they dissociate very quickly. When you grind your beans, you create a lot more surface area for aromatic flavours to be taken away.

This all sounds complex, but making good coffee at home is easy to do; just find a method that works for you. Most importantly, pick a method that’s simple when you’re tired in the morning. If it’s not easy to do at 4am and your kid has woken you up, it’s not worth it.

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