05.Flavour and aroma
What determines flavour and aroma?
Coffee berries (known as cherries), which contain the coffee bean, are the fruit of several species of small evergreen shrub. They’re grown commercially in Australia, but the world’s biggest producers of coffee are Brazil, Vietnam, Colombia and Indonesia. The fruit is usually picked by hand and the beans separated from the flesh of the fruit after drying or by a wet fermentation process, followed by washing with fresh water. The dried beans are sold as “green coffee” (coffee beans before they’re roasted).
- Arabica coffee comes from the species Coffea arabica. This is the best coffee for flavour, but the plants are delicate and require careful cultivation. All coffees on test are made from arabica beans.
- Robusta coffee, from Coffea canephora, lacks the great flavour of arabica coffees but is cheaper because the plants are less susceptible to disease and produce higher yields. Some brands of ground coffee (not included in our test) include robusta blended with arabica beans, but robusta is used more by manufacturers of instant coffee.
Espresso coffee has a more concentrated flavour than coffee brewed by other methods. Espresso machines force hot (but not boiling) water through ground coffee under pressure. This produces a shot of dense black coffee covered by crema, a foam of finely dispersed oil droplets (rich in aroma compounds) and tiny bubbles of gas (mostly residual carbon dioxide from the coffee ground).
Freshly roasted and ground beans definitely make the best coffee.
- More than 800 different chemical compounds contribute to the alluring aroma of good coffee.
- The flavour and aroma of coffee depend ultimately on the genetics of the plant, where and how it’s grown, and how the beans are harvested and processed. But most of the compounds responsible for the aroma are developed during the roasting process.
Keeping coffee fresh in the packet
Unfortunately, roasted coffee is highly perishable; the aroma molecules can evaporate, and be quickly degraded by oxidation. Worse, the aroma of ground coffee deteriorates even faster than that of roasted whole beans. Another problem is that roasted coffee continues to release carbon dioxide gas after roasting, so if it’s packed too soon the bags can burst.
Coffee manufacturers have adopted different technological fixes for retaining freshness with differing degrees of success, as reflected by our scores.
- Top-scoring Illy Espresso Caffé Machinato is sealed in a can under pressure of nitrogen to prevent oxidation. In reality, the coffee is far from fresh as it’s roasted and ground in Italy, but this clever technology is clearly a successful strategy for retaining a “fresh” aroma and flavour.
- The other brands that scored well are packed in airtight bags fitted with a one-way valve that releases carbon dioxide while preventing oxygen or moisture getting into the bag and spoiling the aroma of the coffee.
- Most of the brands that fared poorly use older technology, in which the coffee is vacuum-sealed as a “brick”. This can’t be done before the roasted coffee has released its carbon dioxide, so some aroma is lost even before the coffee is packaged.
How to store coffee at home
- Once you’ve opened a packet of coffee it’s best stored in airtight tins or jars to minimise loss of aroma and damage from exposure to oxygen and moisture. Most experts suggest keeping it in a cool, dark place, such as a pantry.
- If you have more than about a week’s supply, divide it into one-week quotas and store the rest in the freezer. Take one out when you need it, but don’t open it until it’s warmed up to prevent moisture condensing on the coffee.
- It’s never a good idea to store coffee in the ordinary fridge because moisture gets in every time you open the jar to use some.
Coffee is a labour-intensive crop grown mostly by small farmers but marketed by big corporations via middlemen (sometimes referred to as “coffee coyotes”) who cream off much of the profit. Farmers often get little return for their labour, and the problem has been compounded by big fluctuations in the international price of coffee. Fairtrade certification protects small farmers from large price fluctuations and guarantees them a reasonable return.
Agricultural practices introduced in the 1970s have boosted production, but at the expense of the environment. Coffee was originally grown under the shade of trees that provided a habitat for many animals and insects, but many farmers have switched to “sun cultivation”, in which coffee is grown under full sun with little or no forest canopy. This method gives higher yields but causes environmental degradation and requires greater use of fertilisers and pesticides.
Picking a coffee that is certified organic, as well as either Fairtrade or Rainforest Alliance certified, means the environment and workers are treated well.
How much caffeine do you consume? See our caffeine calculator.