I posted this on my blog (www.brewmethod.com) a while ago, but thought i would share it here.
Introduction to espresso coffee roasting
Espresso roasting - how long should you roast and to what finish temperature? The correct answer is whatever tastes best to you. I won't try to tell you what roast depth you should like, or that you should like the same thing i like. But if you're looking for a basic guide, here's what and how i roast for espresso.
Roast time and temperature
Roast time duration, and the end temperature are still two variables you will rarely find on a bag of coffee. The reasons are obvious - different roasters use different thermoprobes all designed in unique ways and while they all may serve the same function (to give a consistent temperature readout roast to roast on the same machine), you can't compare temperatures easily between different roasters.
However i still feel it is useful for home roasters to discuss these variables, if not for sharing exact numbers then at least for sharing roast styles and techniques for particular coffee origins. As a home roaster starting out, i had no clue what temperatures i should be aiming for at what time during each roast phase. Only through roasting, tasting, roasting and then tasting again week after week have i been able to really get an understanding of how to roast well.
I'm not a pro roaster
I won't try to claim that my roasts are better than anybody elses, but i will say that for my own personal taste (which is generally an espresso roast on the lighter side to retain a higher amount of acidity) i am very happy with the results most of the time.
Here is a basic guide that should, in theory, yield some pretty tasty roasted coffee if you have built a home coffee roaster, have it insulated, have a way of easily controlling/changing the input temperature throughout the roast and a method of cooling the beans quickly. Every coffee has different requirements, but in general this is the roast profile that i use as a first test roast with a new coffee, and then adjust accordingly from there based on taste after at least 4 days of degassing.
First step is i pre heat the roaster to around 210 degrees celcius.
Then once temperatures have stabilised, i enable the magic agitation device and dump in the extraordinarily high quality green coffee beans sourced from the likes of Ministry Grounds. Always try to use the same roast mass for consistency - for me that is 480g.
At this stage, i've got heat on a medium setting. My temp control is a dial with numbers, so i have completely variable control at all times during the roast. Temperature in the bean mass generally reaches 70 degrees after 1 minute, 100 degrees after 3.5 minutes. This is the initial drying phase. Once i reach 100 degrees i generally back off the heat input just a little bit.
It's important to keep a very close eye on the rate of temperature increase. I generally do not need to make any further adjustments until 1 minute before first crack. That is at the 9 minute mark around 185 degrees, i reduce heat further to slow the temperature increase to 4 - 5 degrees per minute.
First crack is around 195 degrees at 10:15, and temps increase 4 - 5 degrees per minute from here until i pull the roast at 212 to 214 degrees at around 14:00 - 14:30.
Finishing the roast
Deciding when to pull the roast is critical. You should be sampling from 208 degrees on until you are seeing the roast colour and have reached the roast temperature which you like the taste of in the cup. For me, anything beyond 214 and i start to notice a marked decrease in acidity and sweetness (in some coffees, not all). Anything less than 208 is too acidic and although it still tastes great and super sweet i find it's too much acid for my stomach.
You must cool quickly or the beans will continue to roast on the inside and you risk having over-roasted coffee on the inside of the beans and lighter roasted coffee on the outside.
Bag in a one-way valve bag and seal with a heat sealer (hint: cheap ones on ebay, it's probably okay to skimp on a heat sealer). Degas for at least 3 - 5 days before tasting.
For some more specific temps, refer to my previous roast logs. Note that a lot of my old roast logs were 15 minute roasts. I now generally use 14:15 roasts as i *think* these taste a little better... maybe. I never roast into or beyond second crack, but many do and they can still taste great.
Temp at first crack - a good point of reference
Please be aware that depending on your roasting setup, your temp readings could be completely different to mine, maybe even 5 or 10 degrees higher or lower at first crack. But you can generally use first crack as a guideline for comparing your temp readings with other roasters. For example if i reach first crack at 195 degrees, and my buddy reaches first crack at 200 degrees, then in theory his end temp 5 degrees higher than mine at the same time should, maybe, be a similar roast depth.