August 18, 2016

The Heat is On

A basic guide to better understanding heat transfer on a drum roaster

As roasters, one of the most important things we are always trying to achieve is better control of the roasting process.

And one aspect of this is better understanding Heat Transfer (HT).

Understanding HT involves grasping the mechanisms & factors that drive & control rates of HT during roasting.

Armed with such knowledge we can then determine how to modify & control roast profiles/bean temps & roasting reactions accordingly.

So, let’s get geeky for a bit!

Roasting is the transfer of heat over time &, due to Heat Transfer, is a series of carefully controlled chemical reactions & physical transformations of the green bean into something soluble and tasty.

Happy Days!

The application of heat in roasting determines how fast/slow coffee roasting reactions occur during roasting, affecting the nature of flavour, aroma & colour generated by those reactions, also depending on the rate of HT and duration of the roast.

Reaction rates of HT to and within the bean also affects how the bean temp changes during roasting, depending on reactant concentrations/components of the green beans (ie: moisture, screen size, density etc.) & thermal properties of the beans.

Hence, overall, knowledge of the ‘science’ behind Heat Transfer is essential to helping us as roasters roast more knowledgeably & profitably.



The 3 forms of Heat Transfer are deceptively simple scientific concepts that, once better understood in a drum roaster, will allow us to efficiently control & create a more repeatable, consistent product.


Conduction is the transfer of heat from direct contact between the molecules of a hotter substance to a cooler one – like when you’re smelling the roasting beans in the trier & you tap the hot trier on your lips (or nose) burning them! This is conducted heat!

In drum roasters we have 3 potential sources of conducted heat – the drum, the faceplate and the beans.

Drum/Faceplate to Bean Roasting:

Controlling drum-to-bean conduction is all about preheat temps and controlling the heat transfer at the beginning of the roast in line with the appropriate batch size.

Preheat/starting temps represent stored energy – and we must always start a roast with the right amount of energy!

The higher the starting/preheat temp, the hotter the roaster, the more energy can be transferred via conduction. Preheating/starting consistently with the same amount of stored energy will allow you to roast more consistently thus producing a more consistent product.

For smaller batches, lower the starting/preheat temps if you wish to follow the same profile as when you are roasting a full batch. Less coffee requires less energy.

To match the full batch profile, use the turning point as a way to equalise or find the right starting/preheat temp. If the turning point of the smaller batch is higher than the full batch, then lower the starting/preheat temp to match accordingly next time – remember, with smaller batches, it is always easier to add energy than it is to take it away once your roast has begun.


Convection is the transfer of heat through currents or liquid or gas. In coffee roasting, the transferring substance is air & the receiving substance is the coffee bean.

There are 2 major types of convection – natural convection & forced convection.

Natural convection occurs as air heats up, causing density changes – as air gets hotter it gets lighter & rises, while denser, cooler air falls. This flow then allows heat to transfer through natural movement or buoyancy.

Forced Convection is heat transferred through currents that are moved by an outside force such as a pump or a fan. This is a quicker, more efficient method of heat transfer than natural convection.

In both drum and air roasters, forced convection is the major mode of heat transfer.

Air roasters force/blow air with positive pressure through the roasting chamber and drum roasters use negative pressure, sucking air through the roasting chamber.

The rate and ratio of convection in a drum roaster is directly affected by airflow and energy supplied by the burners. i.e: the higher the airflow and the higher the energy input from the burner, the faster the roast.

Hence, watching the Environmental (Exhaust) Temperature is imperative to making decisions on when to control the burners during a roast – especially at the end of the roast. If you don’t have enough money in the bank or petrol in the tank, you can’t go on holidays or finish your journey!

If you want to take away conductive heat by reducing the burners, you must have built up enough convective heat in the environment/exhaust to be able to do this and be able to finish the rest of the roast on convective and radiant heat without the aid of the conductive heat from the burners.


Throughout the majority of the roast the 2 sources of heat energy are the drum (conduction) and the air (convection). Just before first crack there is a 3rd source of energy – the beans themselves – radiant.

As coffee approaches first crack it becomes exothermic and throws off heat/energy as it cracks. At this stage the roaster must control this release of energy by adjusting the burner down or off, increase airflow or both. This will manipulate the rate of convection (HT) in order to control the total energy (& overall profile of the roast) lessening the impact of the radiant (bean-to-bean) energy of the exothermic beans.

Radiated heat is the most complex type of heat transfer to understand & control in roasting. It is also affected by colour, temperature, density, surface area, finish & orientation to other thermo-producing bodies.

Radiated heat is also thermal radiation that is defined as electromagnetic waves & it occurs naturally between 2 bodies of differing temperatures. Hence, as beans contact hot, roaster gas heat, they mix with and transfer heat to slightly cooler beans in piles near the bottom of the drum.

Bean Movement in Roasting Drums:

During roasting, it is also very important to consider that most of the beans lie in a tumbling pile near the bottom of the drum.

Spiral metal ‘paddles’ inside the drum are spaced accordingly to encourage a good blend/mix of the beans from front to back along the drum’s axis as it turns. This type of axial mixing increases uniformity of convective heat transfer & bean-bean heating.

And of course this heat transfer is also affected by the batch & screen size of the beans, size of the drum, drum speed, materials of the drum and design/spacing of the paddles.


DRUM, Air Bean

AIR, Drum, Bean

BEAN, Drum, Air

The above mantra and below picture represents the periods of the roast at which each type of heat transfer is at its most influential.

At the beginning of the roast it is about the stored, conductive energy in the DRUM – governed by the preheat/starting temp.

AIR or convection becomes important for the heat transfer & formation of body, sweetness and flavour throughout the rest of the entire roast.

Toward the end of the roast the BEANS themselves become an important source of radiant energy – & the dominant way heat is transferred.

At the end of the day coffee roasting is a dynamic process that constantly changes throughout the course of the roast.

As roasters, it is our job to gain a better understanding of each source of heat transfer, how they work and how to get the best results accordingly in relation to our own roasting system.

Next issue, I will tie everything together on heat transfer with specific roast development/profiles & roast data/parameters that will set you on the path to achieving the sweet, sweet smell of roasting success – and maybe even a gold medal at Golden Bean!

About the Author

Anne has over 23 years experience in coffee, having spent the last 10years roasting in both the USA & Australia at all levels from commercial to specialty. Anne is Head Judge for and has also won Golden Bean twice. Now consulting, with her company Equilibrium Master Roasters, roasters can engage Anne as a consultant or attend the monthly roasting course in Melbourne.


Instagram: roastresscoops

MPM Advertisment



p: +61738880566 e: w: f: i: Austraw P/L soon to be trading as Bygreen, is a family owned Australian business manufacturing and importing a range of Food Packaging ...
by Cafe Culture Mag


Almond Breeze Wants to Make You #Instafamous

Sydney, Australia, 19 July 2018: Almond Breeze, the world’s leading almond milk brand, is celebrating the mouth-watering creations made by its social media fans by featuring the tastiest in its new advertising campaign. A min...
by Cafe Culture Mag


5 simple ways to protect your business from scammers this tax time

The end of the financial year isn’t just a busy time for businesses – it’s also a prime time for cybercriminals who try to steal your information and money. It’s a good time to stop and remind your employees of the ...
by Cafe Culture Mag




p: 61 7 5322 5360 e: w: f: @GivexCorporation Givex offers omnichannel POS, gift card, loyalty and stored value ticketing solutions which drive sales for our clients, help them better underst...
by Cafe Culture Mag


Honest to Goodness

p: 02 8310 1800 e: w: f: @organicfoodsydney i: #teamgoodness Honest to Goodness is a leading Australian supplier of certified organic wholefoods & natural products. Our extensive ran...
by Cafe Culture Mag




p: 1800 001 852 e: w: f: @SkipApp i: #skipapp Skip – the smarter way to offer online pre-order, cashless payment and loyalty. Skip is the app that allows customers to skip the qu...
by Cafe Culture Mag


Introductory Espresso Machine Technician Course – July 25-26

Do you have a handy team member in your coffee business that is repairing your espresso equipment but needs some assistance in understanding the technical side of being a coffee technician? This two-day course is designed for n...
by Cafe Culture Mag



Sanremo Australia

p: 02 9898 2200 e: w: f: @SanremoCoffeeMachinesAustralia i: #sanremoaustralia Sanremo Australia is relatively young company driven by a team of dedicated professio...
by Cafe Culture Mag



p: 1300473322 e: w: f: @RedcatPOS i: #RedcatPOS Hospitality software, by hospitality people, for your hospitality business. Redcat provides a locally developed and supported, integra...
by Cafe Culture Mag


Golden Bean pioneering the competition space

It was just over ten years ago that I had a vision as to how we could showcase the hidden heroes of the coffee world. The Coffee Roaster was the little gem working at the back end of the business, developing the product that ma...
by Cafe Culture Mag




It’s been a roller coaster and wonderful ride with Kev, who’s been a star of The Grounds for over 5 years now and we’d like to honour the big guy with 7 Weeks of Kevin – a celebration of all he’s given to The Grounds ...
by Cafe Culture Mag


The Health Nutt

t: 1300 557848 e: w: f: @thehealthnutt1 i: #thehealthnutt The famous Protein Balls, Raw Slices and What The Fudge by The Health Nutt – Sydney’s leading cafe supplier for ra...
by Cafe Culture Mag



Coffee drinkers may live longer

For people who love a morning cup of coffee, and a few more cups throughout the day, there is good news. Coffee drinkers may live longer, according to a new study published in the Journal of the American Medical Association (JA...
by Cafe Culture Mag


New minimum wage takes effect

The Fair Work Ombudsman is calling on businesses to check the new minimum pay rates that apply ahead of a new national minimum wage coming into effect from the first pay period on or after Sunday, 1 July 2018. From this date, t...
by Cafe Culture Mag



Registering a business just got easier

Use the Business Registration Service to help you get your business up and running.     Are you looking at registering a business? The Business Registration Service makes it easy to apply for key business and tax regi...
by Cafe Culture Mag


Cafe Culture Digital Issue 5 – Now available

Latest news, trends, products and reviews – every month.       THIS MONTHS FEATURES: – The Grounds discuss the value of baristas – Mixing with the best – with Alchemy – Uniwell’...
by Cafe Culture Mag

by Cafe Culture Mag




For the first time, Australian farmers can forecast grain yield at the touch of a button, thanks to a new smart phone app developed by Australia’s national science agency, CSIRO. The innovation, known as ‘Graincast&...
by Cafe Culture Mag



Data from the most recent National Visitor Survey (NVS) released today has shown an increase in domestic tourists’ overnight spend on restaurant and takeaway meals, both in terms of the dollar amount and as a proportion of ov...
by Cafe Culture Mag


Don’t pay for government grant information

Watch out for government grant scams… Last updated: 27 June 2018 Are you looking for a government grant to help fund your business? Don’t get caught out by scams and paying for access to government grant information. Go...
by Cafe Culture Mag




p: +61 (0) 3 9872 7900 e: w: f: Bühler is setting worldwide standards in the production of coffee machinery. Product quality, process efficiency...
by Cafe Culture Mag


Harney Teas

t: 03 9099 0293 e: w: f: @harneyandsonsaustralasia/ i: #harneyandsons_australasia/ Harney and Sons luxury tea have a wide range of wholesale products that include the traditional to...
by Cafe Culture Mag


Essential Coffee

t. 1300 324 111 e. w. Essential Coffee provides managed coffee solutions to thousands of businesses across Australia, New Zealand, South East Asia, The Middle East and United Kingdom. ...
by Cafe Culture Mag



Essential Coffee

t. 1300 324 111 e. w. Essential Coffee provides managed coffee solutions to thousands of businesses across Australia, New Zealand, South East Asia, The Middle East and United Kingdom. ...
by Cafe Culture Mag


Milkadamia – macadamia milk:

w. e. f. i. Insta – @milkadamiaau Milkadamia is a family owned, vertically integrated human sized macadamia endeavour. Because our family grows t...
by Cafe Culture Mag


Assisting students with special behavioural needs.

  Café Culture recently was asked to assist in setting up a practice café at the Naremburn School. This kitchen project is being run by 2016 Master Chef Australia session eight winner, Elena Duggan, and is aimed at assis...
by Cafe Culture Mag



Artisti Coffee Roasters

E: P: 66 53 1182 W: Insta: #artisticoffeeroasters FB: @artisticoffee Address: Unit 3/11 craft Close, Toormina. NSW 2452 Living and breathing coffee with 24/7 good coffee vibes! Yes, of cou...
by Cafe Culture Mag


Start your business off on the right foot!

Don’t start a business in Australia without using’s new Starting a Business Guide!   Thinking of starting a business? Or maybe you’re in the early phases of operating? Setting up your own business is exci...
by Cafe Culture Mag


The Gig Economy: Navigating new ways to work

It’s Friday night and it has been a long week.  The fridge is as depleted as you are and the mob needs feeding. But that’s okay, because there are endless choices for dinner and several ways in which it can be delivered to...
by Cafe Culture Mag




Restaurant & Catering Australia (R&CA) has welcomed initiatives aimed at reducing the cost of doing business as well as expanding the accessibility of apprenticeships throughout NSW unveiled as part of today’s 2018 &#...
by Cafe Culture Mag


Is your tax practitioner registered?

A reminder for all small business owners.   The Tax Practitioners Board (TPB) is reminding all small business owners to check their tax agents, BAS agents or tax (financial) advisers are registered with the TPB, if you use one...
by Cafe Culture Mag



Restaurant & Catering Australia (R&CA)  has welcomed the Queensland Government’s  budget measures to support the State’s tourism and small business  sectors  as outlined in  its  2018 – 19 State  Budget...
by Cafe Culture Mag



Cultured Products: Riverina Fresh

P. 1800 993 081 E. W. FB. I. At Riverina Fresh, we’re proudly Australian owned and sourced exclus...
by Cafe Culture Mag



You’re invited to help with the funeral expenses at the Santa Clara Dry Mill in Antigua where workers died in the recent volcanic eruption in Guatemala. And with medical expenses of local children who’ve suffered massive bu...
by Cafe Culture Mag


Our thoughts are with Guatemala

Our thoughts are with Guatemala and it’s people, and with our coffee friends, during this time of hardship. These photos were sent to us from our friends at Terra Negra Trade  and show the force of the volcanic eruption...
by Cafe Culture Mag



What is a Broccoli Latte?

The product, developed by Hort Innovation and CSIRO, Australia’s national science agency, packs a healthy punch with approximately one serve of broccoli in every two tablespoons of powder. A Melbourne café became the fir...
by Cafe Culture Mag


Rubia Coffee Traders Vertical Gravity Fed Destoner

The aim of the Vertical Gravity Fed Destoner is to separate foreign heavy materials encountered in roasted coffee seeds. The design of this system is based on the principle that roasted coffee seeds are lighter than the mass we...
by Cafe Culture Mag


Changes are coming to GST

Make sure your business is ready from 1 July 2018. Last updated: 30 May 2018 From 1 July 2018, the goods and services tax (GST) will apply to retail sales of low value physical goods ($1000 or less) that have been imported to A...
by Cafe Culture Mag




Restaurant & Catering Australia (R&CA) has welcomed the AC T Government’s new One Stop Café program, as announced in the 2018 – 19 Territory Budget. Under the program, café – owners will be able to acces...
by Cafe Culture Mag


The WTBC experience with Tania Stacey

WTBC experience – Tania Stacey The opportunity to participate in the Shanghai WTBC was an experience that helped to build on my knowledge of the modern tea world.  It is a competition platform that suits competitors from...
by Cafe Culture Mag


Countrywide Café of the Year – Winners

In February this year, Countrywide, Australia’s largest Food Service Distributor Group, launched a brand new promotion, ‘Countrywide Café of the Year’. The competition created quite a buzz across the nation, giving away ...
by Cafe Culture Mag



Cafe Culture Digital Issue 4 – now available!

Latest news, trends, products and reviews – every month. THIS MONTH FEATURES: – Insights to what shapes your industry report – Styling with The Grounds – Politics, logistics and direct trade with Phil Di...
by Cafe Culture Mag


2018 Speciality Tea Awards

Royal Hobart Fine Foods has opened up to the blossoming Australian specialty tea industry and created 15 categories which will be awarded Gold, Silver & Bronze Metals n the 29thof July.
by Cafe Culture Mag


Barista Supplies

Proudly designed and made in Australia, the Temptag milk thermometer sticker gives baristas greater control when steaming milk. An important part of serving a great coffee is the consistency in milk temperature. The patented Te...
by Cafe Culture Mag



2018 Breezey Masters Latte Art Competition enjoys a wildly successful 2nd heat in Perth

The WA heat for Breezey Masters 2018 made for an intense spectacle on the evening of May 30th. Once again we had a fantastic turnout of 20 competitors fighting for their place in November’s Melbourne Grand Final. We were extr...
by Cafe Culture Mag


Brazil to host coffee world championships for the first time

In November, the International Coffee Week will host 4 international championships with competitors of over 40 nationalities and thousands of visitors The World Cup of Coffee with its various categories is happening, and it wil...
by Cafe Culture Mag


The battle for Australia’s best brew heats up

The claim of Australia’s coffee capital is officially up for grabs, as international travel authority Lonely Planet publishes its Global Coffee Tour this month. Melbourne has the famed reputation for Australia’s best coffee...
by Cafe Culture Mag



Cafe Culture Digital Issue 3

Cafe Culture Digital Cafe Culture Digital Issue 3 – Reusable cup feature  
by Cafe Culture Mag


Cultured Products – DaVinci Gourmet

DaVinci Gourmet, The Story of Flavour Genius. We believe that Baristas and Mixologists are creative and that they seek perfection to amaze their audiences. We are the contemporary choice for professional drink makers inspired b...
by Cafe Culture Mag


Coffee Waste Is Now Fetching a 480% Premium Over Coffee Itself

“Aida Batlle grows coffee on her family’s farm in the hills surrounding El Salvador’s Santa Ana Volcano. Like generations before her, she had little use for the skin that encases the beans, so she’d turn it into ...
by Cafe Culture Mag