5 minutes to understand the effects of different heating methods on baking

Roasting coffee is the management ofheat with the goal of changing the physical and chemical composition of thebeans. As Candice Madison, director of roasting at raw bean supplier RoyalCoffee, puts it, "Roasting is really about playing with heat."

We know that different types of heatsupplies are created during baking, and their effects can vary during baking. Let'sreview conduction heating and convection heating and how you can regulate themto improve your baking.

Main types of heat

Heat can be transferred in three ways:

1 Conduction heat incoffee roasting

Conducted heat transfer is simple: thetransfer of heat between two objects in direct contact. Conduction is when youtouch something that has just come out of the oven and burn your hand.

In coffee roasting, heat transfer canoccur if any type of heating element (such as a flame) touches the roller, whenthe beans come into contact with the surface, pick or panel of the roller, oreven when the beans come into contact with each other inside the roaster.

Conductive heat transfer plays asmaller role than you might think during coffee roasting. Candice points outthat even in drum roasters, only about 30 percent of the heat transfer comesfrom conductive heat transfer.

2 Convective heat incoffee roasters

Convective heat is the transfer of heatthrough a liquid or gas. Convective heat is when you turn on a hot oven andfeel a blast of hot air blowing towards your face.

There are two types of convection:natural convection and forced convection. Natural convection describes thenatural tendency of hot air to rise and cold air to fall. Forced convection iswhen air is forced to transfer heat through a fan or pump. Almost every roasteruses a fan at some point to draw air into its roaster. But, natural convectionalso occurs in drum roasters, in which the air at the top of the barrel tendsto be hotter than the air near the bottom.

3 Radiant heat incoffee roasters

Radiation, Candice explains, is"energy released through the process of electromagnetic radiation due tothe vibrational and rotational motion of its molecules and atoms." Perhapsthe most famous example of radiation is heat from the sun that travels throughspace through a vacuum, thus heating our planet.

Radiant heat is difficult to measureusing current technology, and is nearly impossible to control in coffeeroasting. Even roasters equipped with infrared burners are using infrared heatto heat buckets (conduction) and air (convection) instead of applying radiantheat directly. Therefore, when it comes to radiation, it's best to just knowthat it has it and let it go.

How do different heattypes affect the baking process

Your baking method and equipment willdetermine how you conduct heat transfer and heat convection. Each machine willproduce conduction and convection to different degrees and allow you to havedifferent degrees of control over them. However, you can always take certainvariables into account:

Bean loweringtemperature

For drum roasters, this is theconducted heat energy that can be stored in the drum. You may want to considerthis when dealing with more compact roasts to emphasize shallower roasts. Candicetells me: "If I'm going to drink coffee to accentuate floral and fruityflavors, I'll apply a lot of heat at the turning point from the start and/orkeep the lower beans on a high temperature. "

Batch size

At some point, the coffee beansthemselves become their own conducting heat source. This means that largerbatches will carry more heat and respond more slowly. To affect large batchesof beans by manipulating them, you will need more energy.

This isn't necessarily a bad thing: aslightly larger batch may be easier to bake, while a smaller batch mayoverreact to every subtle adjustment. Eventually,! Larger batch sizes willrequire more energy at the beginning. It will also be an important source ofenergy to conduct heat towards the end of the baking.

Keep in mind that most roasters do notbake more than 75-80% of the maximum batch size listed by the manufacturer. Asthe beans expand during baking, airflow can be limited and cause problems. AsCandice says, "Stuffing excess beans into the bucket will only mean moreroasting defects, not stronger tasting coffee! "

Air flow

The air flow in the drum is notdirectly related to the convective heat energy. But when beans enter theMaillard reaction and then caramelize before a burst, they release water andcarbon dioxide. The released water has a cooling effect on the environmentinside the drum.

Therefore, if you place the roasterunder constant heat and moderate to low airflow, you may find that the riserate drops slightly around 310°/155°C and 360F/182°C. At these times, turning on theairflow slightly will actually increase your warming rate. The increasedairflow will draw water out of the drum, thus keeping it hot.

Instead, lower the flame and turn offthe airflow to preserve convective heat as you approach a burst. However,depending on the nature of the coffee, you may need to turn it back on again atthe first burst.

Roller Speed

For roasters with variable drum speedSettings, increasing the drum speed means lifting the beans to the top of thedrum that accumulates hot air, thereby increasing convective heat. As with thelower bean temperature and batch size, too high or too low can cause problems.

Candice, the baker, says: "If yourroller speed is too high, it can cause damage to the beans and crush thembefore they leave the roaster. If you turn the drum too slowly, you willnaturally use more conduction heat because more bean chunks will stay incontact with the drum walls for a longer time. This causes the beans topotentially scorch or dissurface. "