How Do You Brew the Perfect Cup of Coffee?
Whether you’re getting ready for work on a Monday morning or preparing for your final meeting on a Friday afternoon, there is nothing quite like a freshly brewed cup of coffee. However, with tasting notes often being as long as your arm and brewing methods ranging from simple cafetieres to state-of-the-art machines, achieving the perfect cup can seem like a daunting prospect.
Thankfully, with scientists and lab technicians apparently being the most devout coffee consumers in the entire US workforce, it’s fair to say that the scientific community knows a thing or two about the best way to get your caffeine fix.
So, in honour of International Coffee Day, we felt it was only right to put our own scientific expertise to good use and scour the research to bring you the ultimate guide to brewing the perfect cup.
A Tale of Two Beans
Before you even begin to think about brewing your perfect cup, you have to be able to choose the right coffee beans. Given the global popularity of coffee, it will come as no surprise that there are plenty of options for you to consider, but first you have to decide between the two main species – arabica and robusta.
Arabica are the most widely used beans, accounting for around 75% of global production. Commonly grown in Vietnam, Brazil, Colombia and Indonesia, they are generally considered to be a superior product as their lower caffeine content and higher altitude growing conditions lead to a sweeter, more acidic cup of coffee, characterised by fruity and floral tasting notes. However, the more bitter and earthy tasting robusta beans also have their uses, primarily in instant coffee and as a component in certain blends to increase their strength and caffeine content.
Once you’ve decided on your species, you then have to get a little bit more specific. Each species is divided into subspecies which, if they are naturally occurring, are referred to as varieties or, if they are produced by agricultural techniques, are known as cultivars. These are the main types of bean available and their signature taste is related to their relative proportions of volatile and non-volatile flavour and aroma compounds… well… in part.
Unfortunately for coffee bean growers and producers, simply harvesting the finest beans isn’t enough to produce an excellent cup of coffee. The fresh, green beans don’t contain many of the flavour and aroma compounds that we traditionally associate with a cup of coffee. This is why they need to be roasted first. During this process they are heated and undergo a complex series of chemical changes before becoming the fragrant, dark brown beans we all recognise.
One of the most important changes is known as the ‘Maillard reaction’. Induced by temperatures of over 150°C, this reaction occurs between carbohydrates and amino acids in the beans and produces compounds known as melanoidins. These contribute to the dark colour and viscosity of the coffee. Other important reactions include the caramelisation of sugars in the beans, which gives sweetness to the final brew, and the breakdown of chlorogenic acid into caffeic and quinic acids which influence bitterness. There are also further reactions that are less well understood like ‘Strecker degradation’, which converts amino acids into ketones and aldehydes that are thought to be new flavour and aroma compounds that weren’t present in the unroasted beans.
Needless to say, roasting coffee beans is a science unto itself and it’s hard to say exactly how each type of bean will react to the process. However, in general, beans that have been roasted for less time produce ‘light roast’ coffee that is brighter, with fruity flavour. Beans roasted for longer periods, meanwhile, produce ‘dark roast’ coffee, which is stronger and more bitter with caramel flavours.
The Daily Grind
Now that you’ve selected the optimal beans, it’s time to begin actually brewing the coffee. Before you open your bag of pre-ground coffee though, to make your perfect cup it can actually be a better option to grind it yourself. This is because controlling the size of the grounds allows you to adjust the flavour of the final product.
The effect of grind size on the flavour of coffee is due to the contact time between the coffee grounds and the water. Contact time is dependent on either one or two factors depending on the brewing method. When using immersion methods like a cafetieres, contact time is dependent on the surface area of the grounds. When using pour-over methods such as drippers, it will also be affected by the rate at which water flows through the grounds.
Usually, the longer the contact time, the more aroma and flavour compounds are extracted from the beans. However, there is a limit, as very long contact times can result in undesirable compounds being extracted, leading to coffee which tastes bitter and flavourless.
Extraction, Extraction, Extraction
The contact time between the coffee grounds and water is only half of the equation for the perfect extraction though. There is also the temperature of the water to consider, for example brewing coffee at high temperatures can quickly extract more desirable compounds, but only up to a point. Using boiling water to brew coffee usually results in the extraction of bitter compounds that can end up ruining your end product.
Extraction requires a delicate balance between contact time and water temperature, and this is usually dependent on your brewing method of choice. For example, espresso is brewed in a matter of seconds with pressurised water at around 93°C, so a fine grind size is preferred. On the other hand, cold brew, which is extracted slowly over a number of hours using water at a much lower temperatures, requires a larger grind size to account for the longer contact time.
This is where research becomes an invaluable tool. There are plenty of helpful online resources that go into great detail about the optimum brewing conditions for different types of coffee and brewing methods. There are even entire books dedicated to the art of brewing the perfect cup of coffee.
Ultimately though, like most things in life, your perfect cup all comes down to your own personal tastes. Given the huge range of beans and the plethora of reasonably-priced brewing equipment available, there has never been a better time to celebrate International Coffee Day by just giving it a go and seeing where your journey takes you. Of course, once you’ve brewed your perfect cup you’ll have to decide whether to add milk or sugar, but we’ll get to that next year!