Every coffee lover longs to brew that perfect cup of coffee. Where every sip is sweet and yet balanced, complex and yet distinct, strong and yet not bitter. Yet our own attempts can often feel distinctly lacking. So what are the components to the perfect cup of coffee?
The first element of excellent coffee which many budding home brewers overlook is the quality of the water used. I mean if you think about it coffee is basically made up of two things; the soluble part of coffee beans and … water. In fact a coffee is predominantly water. It is estimated that water makes up 90% of espresso shots and a staggering 98% of drip or filter coffee. So it is quite simple really, if the water you are using for brewing is high in mineral content or simply tastes unpleasant, that translates into poor tasting coffee.
Just as we are willing to spend money and effort on investing in delicious coffee beans, so we ought to be willing to spend time and effort investing in quality water. Water quality is often described in terms of soft and hard water. This basically refers to mineral content and alkalinity in tap water. Soft water is treated water with low mineral content in which the only ion is sodium. Hard water by contrast is treated water with high mineral content, especially of magnesium and calcium. You can often find out the distinctives of your tap water through your local council, and this differs within countries and even within cities. Hard water negatively impacts both the flavor of the coffee and also the longevity of coffee equipment. If you want the perfect cup of coffee, you need the perfect water.
So if your local water is particularly hard or unpleasant, what are the alternatives? There are basically three options. The first is to transition to using bottled water. Bottled water is easy to acquire, and is a simple way to ensure the quality of the water you are using. However, if you make coffee regularly the cost does add up, and even more pressingly this is fairly terrible for the environment. The second option is to use some form of filtration system. This is what most cafes opt for and once set up does make life simple. There are various kinds of filter systems available for either commercial or domestic settings. If you are considering this, one innovative new filter system designed specifically for coffee brewing is the Peak Water Pitcher which we recommend. The third option is to use satchels of water cleansers. These are beginning to come into vogue and are a superb way to ensure optimal water conditions. Our favorite of these is Third Wave Water which again is specifically for coffee brewing and meets the Specialty Coffee Association’s (SCA) standards for water quality.
Another common error made in coffee brewing is incorrect water temperature. In simplified terms the heat of the water used for brewing affects how quickly or slowly the coffee extracts. It is generally recommended that the ideal water temperature for brewing coffee is 195 to 205°F (90.5-93.3°C). Especially a few years ago it was commonly asserted that you would burn the coffee grinds if you used boiling water. However, this has now been decisively shown to be untrue and many leading coffee experts advocate using water that is close to the boil. It is true that water that is too hot can extract unpleasant burn-like flavors from the coffee beans, but this is less common today when beans are often roasted lighter.
The other often overlooked aspect to water temperature is that water temperature is actually less important than slurry temperature. The ‘slurry’ is the mix of hot water and coffee grounds in the given coffee maker. The slurry is the place where the coffee extracts but depending on the coffee maker, the slurry can lose heat quickly leading to sour tasting coffee. So for example, pour over coffee makers such as the V60 or Kalita Wave have a large opening at the top and so the slurry temperature drops quickly. It is for this reason that coffee experts are increasingly advocating higher water temperatures for open topped brewers as this leads to a hotter slurry temperature.
There are basically two different types of coffee brewing that you need to get your mind around; infusion and immersion. Also all the different types of coffee makers fit into either one of these categories or somewhere in the middle.
An infusion coffee brewing process is one in which the water passes through the coffee beans. This includes pour over, drip coffee, espresso, and Aeropress. Infusion brewing methods often make coffee that tastes lighter and brighter because there is a limited time in which the water is in contact with the coffee grinds.
An immersion method, by contrast, is one in which the coffee grinds are soaked or ‘steeped’ in the hot water for a protracted period of time before the water passes through. This includes French Press and Cold Brew. This leads to coffee that tastes a lot heavier and bolder. There are also various coffee brewers such as the Aeropress and the Clever Dripper which can be used either as immersion or infusion brewers.
To make the perfect cup of coffee we need to understand at least something about the process of coffee extraction. Extraction is really a fancy word to indicate how much or how little of a coffee bean has been ‘dissolved’ or extracted into the cup of coffee. Basically coffee beans are soluble which means that just like sugar particles they dissolve if they come into contact with water, and the hotter the water is the faster the beans dissolve. A coffee bean is 30% soluble and 70% insoluble and so the taste of our coffee is really a reflection of how much or how little of that 30% has been extracted. The SCA recommends that the ideal parameters are between 18 and 22%. So if your coffee tastes less than perfect then the technical explanation is that either you have extracted too much or too little from your given beans. These are where the terms under and over extracted come in. The perfect coffee is the balanced coffee where neither too much nor too little is extracted.
This in part comes down to the different flavors of coffee beans that are extracted at different points in the extraction process. In coffee beans first the fruity and acidic notes are extracted, then the sweetness, and finally the more bitter notes. So in terms of flavor notes first come the fruity and bright notes, then the sweeter ones such as nuts, caramel, chocolate, and finally the heavier notes such as ash, malt and tobacco. Optimal extraction is to get the maximum amount of positive compounds from the beans and the minimum amount of the negative compounds.
Regardless of brewing method there are basically four different ways that you can either increase or decrease extraction; grind size, brew time, water temperature, and water to coffee ratio.
Grind size is perhaps the single most effective way to alter coffee extraction. It really comes down to surface area; finer grinds have a cumulatively greater surface area while coarse grinds have a cumulatively smaller surface area. And so fine grinds extract more quickly while coarse grinds extract more slowly. This is the reason that espresso which has a 20-30s contact time between the beans and the water uses an exceptionally fine grind while cold brew which has a 12-24 hour contact time uses a very coarse grind. And so if your coffee is tasting sour or overly acidic then it is probably under-extracted and the grind size needs to be finer. Similarly, if it tastes bitter and harsh the grind size should be set to a more coarse grind setting.
Brew time also plays into coffee extraction and hence the taste of coffee. The general rule of thumb here is the longer you brew, the more you extract. So for greater extraction you lengthen the brew time while for a lesser extraction you decrease brew time. This brewing parameter is closely connected to grind size, so usually a fine grind goes with a short brew time while a coarse grind is used for a longer brew.
The final major parameter that the brewer can change to increase or decrease extraction is the coffee to water ratio. The SCA recommends that the golden ratio is 1:18 coffee to water. So this ought to be the base ratio that home brewers use. And from there you can either increase extraction by using more coffee or less water, or decrease extraction by either using less coffee or more water. In general however, this should be one of the last parameters to change as it is easy to get wrong and many coffee recipes use specific ratios for a reason.
With all of these brewing parameters it is important to experiment to find the perfect cup of coffee for your palate. The perfect cup of coffee is attainable but will take time and effort so don’t give up!