Roasting Coffee is a lot of heaving lifting, monitoring time and temperatures, heat and air, risk of fires, risk of over roasting, under roasting and simply cruising through an ideal roast takes hard work.
I roast on a 25 kg 2014 Diedrich Roaster and it fits the roasting needs where I roast 2 to 3 days a week for a few hours a day. We have room to grow, but using the roaster has costs associated with it because of the occasional part replacement and the life of the machine. Fortunately, a well maintained and clean roaster can last a long time.
Roast times and temperatures vary but a light roast of about 38 pounds can take only 8 to 10 minutes. These roasts are generally the single origin or micro lot coffees although Rooster Roast is a pre-roast Blend that is the same roast time and temp. as the single origins.
A medium roast like Lupara espresso may take 10 to 11 minutes but a medium dark like Rocket or Fruition may take about 11 to 12 minutes while the dark roast like Organic French is going to take 12 to 14 minutes.
There is no way to set the time and just chillax and let the coffee do it's thing while roasting in the drum so I look for roast development through the sight glass during roasting and also listening for the crack. The roasting process includes "DT" Development Time and as Roasters we talk about "DTR" Development Time Ratio
- DT or Development Time is measured in minutes and seconds from the onset of the first crack to the drop temperature.
- DTR or Development Time Ratio is The percentage of the total roast time that happens after first crack, calculated as: DTR = (Development Time ÷ Total Roast Time) × 100.
The development Time is after the maillard reaction which is when the beans start browning and the sugars start to develop in the roaster. I like to think of this as the time from when the coffee changes as seeds to beans or from nothing to something. The shortest DT and a carefully roasting Coffee by heat, weight and airflow will yield the nuances of the how the coffee is grown and processed from everything to the soil it comes from to the processes of how it's pulped and washed and eventually dried and dry milled for roasting, this is a light roast coffee; one that showcases the nuances of the bean. The short DT of a great tasting coffee would be considered the sweet spot. The sweet spot can further be explained by DTR. This is the time from the first crack to drop time divided by the total roast time x 100. If the coffee tastes great on a DTR of 20% of a 10 minute roast then you could say that the final 2 minutes of the roast was the best time for development to bring out the nuances of the coffee.
The longer the DT and the higher the DTR the more the coffee is going to taste roasty or potentially smoky and even so far as burnt if not done correctly or if the beans are not handled correctly.
Thanks for taking a deep dive into coffee roasting development times and the development time ratio with me and if you enjoyed this! -Chris M