Many of us (at least in the older years) will probably enjoy a nice cup of coffee at some point during the day, whether that is an iced late, americano, cappuccino or some incredibly complicated order with syrup and cream that ends up looking pink. But what exactly makes the perfect coffee (using science of course)?
First up: choose your coffee bean.
The size of your grind is one of the most important factors, and it’s all up to taste! If you want a stronger coffee, use a finely ground bean. It will mean there is a bigger surface area for the beans to be in contact with water. This greatly decreases the extraction time which tends to lead to an increase in the strength of the coffee bean. For example, Turkish beans are boiled, finely ground and thus generally make a very strong coffee, so watch out!
Ever wondered why coffee often just tastes better when bought for too much money at a coffee shop? Well, although part of it is purely psychological, the freshness of the beans also plays a big factor. Both how freshly they have been roasted as well as how long ago they were ground change coffee quality. Coffee shops often freshly roast and grind their beans to allow for the best taste in their coffee. As coffee beans are volatile, the longer they stay unextracted, the less flavour and aroma they have. After a couple of weeks, the natural oils oxidise and end up turning rancid.
Next up: get your water right.
The temperature of water also changes the extraction time. Higher temperatures of the water decrease the extraction time of the coffee bean as well as the solubility of the caffeine in the water so a coffee brewed in cold water can be expected to have a lower caffeine level as well as a lower bitterness. However, be careful not to go too far the other way, with high temperatures hurting just as much, leading to over-extraction and an incredibly bitter brew.
The type of water also changes the taste. Water in London, as most of us will be aware, is considered ‘hard’ which means the water has a high mineral content (specifically calcium carbonate). The type of water can change what flavours are brought out in the coffee, changing the taste to acidic, fruity, or creamy to name a few. This is because coffee needs metallic ions to bond to the flavour molecules in the coffee grounds, but each metal ion leads to a different flavour. For example, high magnesium content leads to a fruitier flavour (as well as aiding with flavour extraction) while calcium highlights the creamier flavours within the coffee, dulling any acidic qualities. Carbonate, although helping to neutralise the acids in the coffee, if combined with calcium forms calcium carbonate, which can be a problem for equipment.
Long story short, the water used for your coffee should have a hardness of between 75ppm and 250ppm.
Ratio of beans to water is another important factor in making the perfect brew. This is often down to the maker’s preference and unfortunately is not something I can tell you for definite as it depends on your previous choices (e.g. ground size etc.). Some sites cite a ratio of 17.4 units of water to 1 unit of coffee, but this is, in my opinion, somewhat subjective.
Finally: perfect your method.
I’m sure many of us have watched someone making a ‘professional’ coffee and thought why do they have to push the beans down so hard in the little silver holder thing? Well, the answer to that incredibly specific question is here. The process, called tamping, packs the coffee grounds which aren’t uniform together, creating a resistance to the hot water that is going to be run through it. This allows for optimum extraction (as extraction time is increased) which is why the tamping needs to be done uniformly and it should be made sure that there are no big air pockets in the coffee (this can happen with big differences in grinds) as it will change the level of extraction that happens.
If a big barista machine is something you only see in cafes, coffee machines are another way to go, but unfortunately that involves quite a lot of engineering and not much user preference (and due to the variability of machines, I could probably write a whole article just on that). Due to this I’ve decided to focus on other methods, such as the French press. The theory behind it is that you let the coffee be extracted by the water before separating it out just before drinking. When compared to filter coffee, it allows for more oils to get into the water as they haven’t been stopped by the filter paper. Personally, I probably couldn’t tell the difference between the two, but some people do swear by it.
So, now that you have the theory behind a coffee, and how to optimise the experience for your own taste preferences, go get a cup of brew (or hot chocolate if you’re not a coffee drinker), relax, and enjoy your day!
