Coffee is complex. There are over 800 compounds within coffee, many of which are created during roasting, far greater than wine. Roasting coffee is the process of initiating a series of chemical reactions.
Roasting process
- The roasting process begins and the coffee beans warm up in the first few minutes. After four minutes the beans begin to dry out and release a grassy smell and the beans turn a bright green color. The beans are endothermic during this stage, absorbing heat.
- The beans turn a yellow color releasing steam and smell like hay, then toast.
- The beans turn tan to light brown, a caramelization of sugars and the Maillard Reaction. The beans begin to swell in size and lose chaff.
- First Crack, the beans make popping sounds like popcorn or cracking pencils. This is caused by the releasing of water through steam and fracture of the cell structure. The beans surface looks mottled. This marks the stage where the bean becomes exothermic, releasing heat.
- After the first crack, most of the moisture has been released and CO2 builds. The surface smooths out. City Roast
- A short period of time between first and second crack. The color turns dark quickly, caramelization of sugars. Full City Roast
- Second Crack, the beans make a crackling sound like breaking toothpicks caused by CO2 fracturing the cell structure. The beans are large, dark color with no signs of oil.
- After Second Crack, oils begin to appear on the surface. Vienna Roast
- French Roast, dark colors and oily surface.
- Stop the roast to your desire. Cool the beans off with a fan.
This is the general process for roasting coffee. Each roaster roasts differently so it takes time getting used to your roaster. Recording time and temperature intervals will help you understand the process. Recording color and aroma stages will also help. Roasting also depends on environmental conditions- hot or cold outside, humidity. For a detailed process. Taking detailed notes while roasting and tasting results will help you roast better. The next time, you can make minor adjustments.
Roasting errors
Errors can occur while roasting which can have a negative affect on the coffee.
- “Tipping” are black marks that appear on the side of the bean if heated too quickly. This will cause the exterior to be over-roasted and the interior is under-roasted.
- “Baking” or “stalling” the roast is where there is heat loss between first and second crack. The roast losses momentum and the coffee will have a flat, baked quality.
- If the beans do not cool off quickly enough after roasting, the carry over heat will continue to heat the coffee causing them to taste flat.
Freshness
Roasted coffee
Roasted coffee is perishable. Immediately after roasting, the beans omit CO2 for several days. As CO2 stops being produced, oxygen settles within the coffee bean. This is when the coffee begins to oxidize slowly and the subtle flavors begin to fall off. The coffee degrades in quality, eventually going stale. Note the roast date.
Roasted coffee should be stored in a cool, dry place away from heat, air, light and moisture. A cannister with a good rubber seal stored at room temperature. Treat coffee like bread. It can be frozen, but be careful of moisture and condensation.
Green coffee
Some roasters are freezing green coffee in vacuum sealed plastic bags to preserve freshness. This is happening at some roasters warehouses and also at country of origin before shipping. In theory, the green beans are susceptible to moisture in the air, oxidize and pick up off-flavors from the burlap bags. Freezing coffee will slow down the aging process and prevent flavor loss. I have not yet tasted coffee frozen before roasting.
New Crop and Past Crop
Coffee is harvested once a year and commercial roasters purchase coffee seasonally. Generally coffee will be warehoused for a year until the next year’s coffee arrives. Coffee loses moisture over the year affecting the acidity and quality of the coffee. Past Crop coffee refers to coffee from the year prior, which has lost much of its freshness and moisture.
Most home roasting suppliers are generally buying small amounts of coffee which will last them 3-6 months. Watch the supply of coffee throughout the year from your supplier. Running out or changing coffees is a good sign that the coffee is fresh. When I order coffee, I write the purchase date on the bag of coffee to know how long I have stored the coffee. I generally consume coffee within 3 months of purchase.
