How to Roast Coffee at Home

How to Roast Coffee at Home

Roasting at home is a great way to get the freshest cup of coffee you can. Green coffee beans - stored correctly - can stay fresh for around 12 months from harvest – roasted coffees start to lose their freshness after one month or so, so the idea would be roast what you need for a couple of weeks, rinse and repeat.

Roasting at home gives you full control over the roasting process, allowing you to tailor it to your tastes and preferences.
But what exactly goes into roasting coffee, and what do you need to get started?

Green Coffee Beans

To get started, you will need some green beans – the raw unroasted product that roasters turn from green to brown. Green coffee comes in huge 60kg hessian sacks, but to roast at home, unless you have a serious caffeine problem, you won't need to be purchasing this much! Luckily you can get a range of small green coffee bags from us - check them out here.
Remember that there are different types of coffee out there, with varying degrees of quality. Whilst the Arabica and Robusta conversation we hope is well understood, there are so many other things to consider when purchasing your green coffee: scoring, varietal, processing methods, altitude etc. These will affect the taste of the coffee and how you choose to roast it.

Raw green coffee beans
Green coffee beans

Experimenting is the fun part too! Roasting at home will broaden your coffee knowledge so much.

Note: it's good to remember that when you roast coffee, you will lose up to 20% of the original weight. The inherent moisture in a green bean is lost in the roasting process, depending on how dark you choose to go. For example: 1 kilo of dark-roasted coffee may produce 780g of roasted coffee – a loss of 22%. 1 kilo of medium-roasted coffee may produce around 850g of roasted coffee – a loss of 15%.

Equipment Needed

You can roast coffee at home quite simply and cheaply, or you can go all out and get some remarkable kit that will do a cracking job for you. Really, you can make this as little or as much of an investment as you like. Here are a few of your options:

Popcorn Maker

One of the simplest and most economical ways to roast coffee at home is with a popcorn maker. Like some coffee roasters, they use hot air circulated through the chamber to heat and circulate the beans while they roast. They are relatively low-cost and easy to operate, making them ideal for those just getting started with home roasting. However, they do not offer much control over the roast profile, so it may take some practice before you get consistent results.

Drum Roaster

Drum roasters are a more advanced option for those who want more control over their roast profiles and higher-quality results. The units use a rotating drum inside the machine that turns whilst hot air is circulated, allowing even heat distribution throughout the beans and giving you more control over how quickly or slowly they roast. They tend to be larger than other machines, so if counter space is limited, this may not be your best option.

A Coffee Roasting Sample Spoon
A sampling spoon from a drum roaster

Roasting Pan

If you don’t want to invest in any special equipment, you can always use a good old-fashioned metal pan on your stovetop. This method takes longer than an air or drum roaster but it’s still possible to produce good results if you pay close attention and stir constantly as the beans roast. You will need an idea of temperature, so a basic thermometer will help, so that you can monitor your beans’ temperature throughout the process. This method produces quite a bit of smoke, so make sure that you have enough ventilation.

There are professional small roasters too, such as the Ikawa (which we use ourselves), as well as the Roest and HB roasters.

How to roast your green beans at home

Once you have all your equipment ready, it's time to start roasting your green beans!
To begin, preheat your roaster until it reaches a stable temperature that you want to commence roasting at (charge temperature). This will vary depending on your method and batch size. Add your raw green coffee beans into your equipment, and off you go... It's a fascinating process, which you can read more about here.

The first thing that happens to coffee beans during roasting is that the moisture within the bean begins to vaporise, and as the water vaporises, it expands and causes the beans to swell. 

The beans then begin to change colour. The heat from the roaster starts to break down the chlorogenic acid that's present in the beans.

Chlorogenic acid gives green coffee beans their characteristic colour, so as it breaks down, the beans start to turn brown. The set of reactions that occur at this stage is known as the Maillard reaction - the same phenomenon that happens when anything browns (like bread and meat).

You'll then notice a popping sound - this is known as first crack, and is normal and exciting to hear the first time around. Coffee is not soluble until after first crack, so don’t try it!

As the roasting continues, more and more moisture is lost until eventually, all that's left are dry, roasted coffee beans. At this point, the colour will be a deep, rich brown, and its size will have increased by about 30%.

If you'd like further control over how dark or light your roast becomes, experiment with different temperatures or lengths of time when roasting; remember that darker roasts tend to be more bitter, while lighter ones offer more complexity and sweetness.

If you want to go for really dark coffees – then keep going and push them until you hear a second crack. Second crack is a little harder to hear. At this point, the cell structure of the coffee beans begins to fracture and the oil begins to migrate from the inside of the bean to the outside. The appearance of the coffee becomes much darker and oily, and you will often find that the surface of the coffee bean has been damaged – you will see little craters where the energy has been so great within the bean it has blown it up from the inside.

Dark Roasted Coffee Beans
Dark roasted coffee - definitely at second crack!

With each batch that you roast, you can adjust based on previous experiences until you achieve just the right flavour balance for yourself.
Once done roasting, remove them from the heat as soon as possible as you don’t want to over-roast your coffee. Once removed from the heat, get them cooled as quickly as possible using cool air/fan / ambient air.
Make sure you store your beans in an airtight container and only grind what you need when you need it!

With just a few pieces of equipment and some experimentation with temperature levels and times during the roasting process, anyone can learn how to roast their coffee at home! So go ahead - embrace the science behind creating delicious cups of coffee by giving home-roasting a try!

Let us know how you get on, as we would love to be a part of your journey.

Best wishes from the Rounton Team

Buy green coffee here
Buy roasted coffee here