Coffee with the biggest caffeine hit is likely to have come from the robusta bean type. These coffees may be more likely to have a bitter taste and perhaps heavier earthier tones. Instant coffee is more likely to have been made from robusta beans to capture more caffeine in the granules. There are also several coffee shops that favour the robusta bean.
Robusta coffee beans count for around 25 to 30% of worldwide coffee production and the tree is more hardy and grown at lower altitudes (below 1000 meters) in higher temperatures (upto 30 degrees celsius). The robusta bean may be more likely to be circular shaped and with a straight line split down the middle. It tends to be cheaper, with a less pronounced aroma but more full bodied. Robusta can vary in quality due to growing conditions and processes, and there has been a movement to upgrade the reputation of the bean with more care and attention in the growing, processing and roasting techniques. Largely though robusta beans would be more inferior coffees – but if caffeine levels are the priority then with often double the caffeine of arabica beans there are some benefits!
The higher altitude grown (often 1500 to 2000 meters asl) arabica beans are usually sweeter, more flavoursome (fruity, floral, delicate, smooth) with a more pleasing aroma. They can be oilier and darker and have a more oval elongated shape with a probable split which is more S shaped. Most likely grown at temperatures of high teens to low twenties celsius, and with more shade (in the company of a wider biodiversity of other plants).
There are many sub-species of coffea and there is a possibility that in future increasing the genetic variation may become important to protect coffee from vulnerability to disease and climate changes.
Coffee fruits are called coffee cherries and most move through a colour cycle from green, then yellowing, to red when ripe. The seed, inside the coffee cherry is what is used to roast and create our coffee drinks. In order to ready a coffee bean for roasting it has to go through processing to remove the skin and flesh of the coffee cherry (the pulp, the parchment and the silverskin).
In fact, inside the cherry – there are normally two parts of the coffee seeds which grow with a flat face facing each other – these are the faces that feature the characteristic split in the coffee beans we see.
A coffee seed (bean) before roasting is normally a yellowish green colour and known as a green bean: once roasted they gain their brown colour.