Are you roasting or baking?
25 March 2015
In cuisine, roasting and baking are both dry-heat cooking methods. These cooking techniques use hot air to transfer heat. Both methods brown the exterior of food, adding delicious flavour – think crispy chicken skin and crusty bread. Roasting used to signify food cooked over an open flame, such as an outdoor rotating spit-roast. Today, roasting at home is usually done in an oven. This makes the difference between roasting and baking a bit confusing, when the same oven can both roast a chicken and bake a cake.
So is coffee roasted or baked? In Ethiopia the most common way of cooking coffee is by pan. Most Ethiopians roast their own coffee at home in what is essentially a wok. It is the only place in the world I know of where spruikers will run up to your car window as you drive into a town and wave a small plastic bag of 1 kilogram green coffee in your face. Rural Ethiopians often have a plastic tarpaulin laid out in the front of their home to dry their own year’s supply of household coffee cherries straight from the tree.
The traditional Ethiopian coffee ceremony involves cooking coffee in a wok over a naked flame. The coffee is continually tossed, a bit like an Asian stir-fry. The heat is transferred more by conduction than radiant heat, as opposed to our roast chicken or baked bread analogy. The coffee is then crushed in a mortar and pestle made from a small tree trunk. The pulverised coffee is put in a metal pot similar to a Turkish Ibrik with water, and is then brewed over the same flame that just cooked the beans. Despite the relatively simple roasting and preparation method, it actually tastes quite delicious.
Now let’s switch over to a more modern day high-tech comparison. Coffee-Tech is an Israeli company that constructs some very sophisticated coffee roasting equipment. One of their sample roasters uses the same simplicity of conduction cooking in the form of an enclosed copper ball. But, they also have production roasters that utilise a number of heat transfer methods, including Infrared Radiation, Thermosiphon, fluid bed, and forced convection drum roasting.
Now let’s have a look at the technicalities of drum roasting. The variety of drum roasters available is impressive. In Brazil, the most common roaster would be the Palini Alves sample roaster. Now I would consider this to be the closest of any roaster in the world to our original ultimate definition of roasting. That is, it utilises a perforated drum that rotates over a naked flame in close proximity underneath the coffee beans. I used to shake my head at the control required to avoid charring the beans, but it can and does produce a very nice tasting coffee.
Some Italian drum-roasting equipment utilises this same principle, except the burner is above the perforated drum. This can produce fantastic tasting coffee for espresso, probably because it creates a complex balance between radiant and gentle convection heat, with virtually no conduction heat. Other Italian drum roasters use ‘forced convection’ where the heat source burner is not in close proximity to the coffee beans; it can be metres away. The challenge with this style of roasting is that it relies heavily on high velocity hot air with minimal radiant heat. To use our kitchen oven cooking analogy, this is a case of using fan-forced convection heat.
The result, if done improperly, can be a product that is too dry inside and loses some of its interesting flavours. I find that this method of roasting, however, can be good for quicker drip-filter style coffee roasting, but it is limited when it comes to roasting more complex flavours for espresso. It’s a stark contrast to the traditional Ethiopian style of roasting, which is almost completely conduction heat, with some radiant heat, and virtually no convection heat.
When using a solid drum roaster I find it a little more problematic trying to achieve a balance of radiant heat and gentle convection heat without too much conduction heat. If the heat source is an atmospheric burner immediately underneath the drum, (think barbecue burners), I find that there can tend to be too much conduction heat. This is often because stainless steel is a poor conductor of heat and you will get tipping and scorching from the hot metal which will taste very unpleasantly ashy. That is why some manufacturers use a double wall drum with air that acts as an insulator to reduce scorching.
Indirect heat in close proximity to the drum, in the form of a power burner, can solve this problem as well. It results in a nice mix of radiant heat and gentle convection heat, which results in a more complex flavour profile.
The application of the heat to the bean is measured in the Rate of Rise (RoR). Thanks to modern technology, we can track this on a graph on a computer. However, in my experience it is often the type of heat that is cooking the bean that can have a greater effect on the end result: how the coffee tastes. We’ve conducted conduction heat and air-flow tests, and have found that the velocity of air can completely mask RoR in terms of flavour development; both good and bad.
In terms of roaster innovation, I have to mention Mark Beattie at Coffee Roasters Australia. Mark is working with Ram Evgi at Coffee-Tech in Israel. Together, they are coming up with lots of exciting new developments. Mark has developed a great roast data logging system in Australia and Ram has developed engineering innovations.
The Thermodynamic drum is one example which features a triple-layered drum, utilising a solid copper layer sandwiched between two layers of perforated mild steel. Ram has also pioneered the ‘Vortex’ air inlet at the back of the drum to evenly stir heat into the roasting drum.
It is exciting to be involved in the coffee industry at the moment with so much dynamic innovation happening. Regardless of the argument about roasting versus baking, in the end, it should always be about the final result: the taste!