Developing Flavour by Roasting

How do I achieve best tasting coffee? What actually happens during the roasting process? below is an an overview of how we consistently roast beautifully tasting coffee, day in, day out, every season at Mahalia Coffee. 

Roasting stages

There are three main stages in roasting: drying stage, browning stage and development stage.

1. Drying Stage

The coffee bean has a moisture content of 10 - 11.4%. We need to rapidly reduce the moisture content in the bean. The drying stage typically lasts 3 - 8 minutes with a traditional drum roaster, depending on how many kilos you start with, the larger the batch, the longer the time extends. The temperature in the end of drying stage is typically 160 ⁰C. Especially with drum roasters, you need to be careful so that you do not burn the beans by having too much heat at the beginning of the roasting process. The drying stage is also important for collecting energy for the bean because the last stage of roasting is exothermic (heat producing).

2. Browning Stage

From 160 ⁰C the coffee starts to smell like baking bread, a sweet vanilla cake a the middle stage of cooking. This is when the aroma precursors are starting to convert to aroma compounds. Even though browning stage is after drying stage, some drying continues throughout this stage in the roasting process.

At the end of the browning stage, a term called the Maillard reaction is starting. It is responsible for browning. The Maillard reaction is responsible for reducing sugars and amino acids react making hundreds of different aroma and colour compounds known as melanonids. This is the stage when the roast naturally slows down – and roastmasters also want to slow the rate of rise during this stage  – to ensure optimum flavour development. In the end of browning stage, the coffee will start to pop. This is called the first crack and the development stage starts.

3. Development Stage

In the beginning of development stage, the reaction becomes exothermic and the coffee cracks. During drying and browning stages, the bean has collected energy that makes the coffee explode. Development time is when the wanted aroma compounds are developing. If we do not slow down the roast at development stage, we easily get coffee that is smoky tasting and flavour is too sharp from applying too much heat from the burners of the roaster.

The length of development stage is typically 15 – 20% of the total roast time depending on the desired flavour profile and roast degree.

Roast degree

Roast degree is one of the most important indicators with the roast. It can be measured by time, temperature, a colour meter and by cupping. Roasters usually want to enhance coffee’s own flavours and decide the roast degree. Typically, light roasted coffee is more acidic, and dark roasted coffee is more dark cocoa. Also, fruity flavours are more common on light roasts, and roasty and flat, dull flavours are more common on over dark roasted coffee. Light roasted coffee is fruitier due to high amounts of an organic compound, 5-hydroxymethylfurfural. When roasting goes further, this compound breaks down to less fruity compounds. The number of sulfuric compounds increases, which can produce roasty and smoky tobacco flavours when the coffee is allowed to roast for too long. Lighter roasted coffees brings out more of the character of the coffee origin. It is easier to distinguish a lighter roasted coffees true flavour profile from each other than dark roasted coffees. 

Roast time

Even though roast temperature has the larger role on coffee flavour profile, total roast time and time of each stage are also as equally important factors. If you roast in a shorter period of time, you will get more desired aroma compounds. However, be careful not to burn the outside of the beans, and therefore contributing to major underdevelopment in the center of the bean. Coffee’s total flavour (fruity, berry-like, chocolatey, nutty al togetherness) is stronger from a well throughout and executed roast plan. 

Roasting for filter or espresso?

Have you ever thought what is the difference between filter and espresso coffee? Filter extraction is done by gravity and its’ process is quite gentle. You may use very aromatic and more acidic coffee for filter. On the other side of brewing you have espresso, this is extracted with generally 9 bar pressure. That means more flavour is extracted to the cup through pressurised water. Sometimes coffee roasted for espresso might not be as good when brewed as filter coffee and vice versa.  Depending on the bean, and not for the extraction method, I aim for a golden middle way between too light and too dark so that coffee is suitable for both.

Traditionally espresso was a darker roast with low acidity and big body. Filter coffee is roasted differently but roast degree is typically lighter than for espresso. Nowadays roast styles are more flexible than the older traditional styles with the knowledge base within the specialty industry growing exponentially. For example, our Ethiopian Yirgacheffe. I decided this origin needed to be for espresso and Filter, was roasted lightly with a quick roast profile which made it really aromatic with low roastiness. Body was rather juicy than heavy. On the other hand, we want some of our coffees to be more full bodied for espressos. Then we roast with different profile parameters to develop flavour and decrease acidity.

All in all, learning to roast is a never-ending journey. You can always learn more about the bean. The most interesting part of my work is trying to find out the best possible roast profile to bring out the all the coffees best flavour characteristics. 

Here is a fail-safe way to steam silky, smooth cow, almond, soy or oat milks.

Note the varied finish temperatures for cow to plant-based milks.

Step 1. Choose your stainless-steel milk pitcher according to the drink you will be making. I.e., 360ml for one standard latte or cappuccino or if you are making two, choose the 600ml pitcher.   

Step 2. Fill the pitcher with the amount of desired milk you want to heat. Use the lines inside the pitcher as a guide. If there are none, fill it halfway. Before steaming, purge your steam wand.

Step 3. Lift the steam wand so that it's slightly tilted. It might help if you lean the pitcher to the steam wand from the pitcher's pouring spout.

Step 4. Place steam wand tip to the centre of the pitcher and tilt the pitcher to either side. At start, push the steam wand's tip underneath milk's surface to avoid making large bubbles by drawing in too much air.

Step 5. Turn on the steam wand. To create dense foam in the milk, lower the pitcher right away in the start so that the steam wand's tip comes to the surface again.

Step 6. When you have created enough textured foam, lift the pitcher again so that the steam wand tip goes underneath milk's surface, but the milk is still moving in a circle like motion. By dropping the steam tip in, stops air drawing into the milk creating textured foam.

Remember, you control the amount of foam by checking how much the milk's level rises in the pitcher.

Step 7. Heat the milk by staying right underneath the milk's surface. Heat the milk to 66c, plant-based milks to 60c – 63c

Step 8. Turn off the steam wand when the pitcher is starting to "burn" the palm of your hand (~55-66c). Check the milk's temperature with thermometer and learn how hot 55-66c feels in your fingers.

Step 9. Wipe and purge the steam wand right after every use.

Knock the pitcher onto the table to break any small bubbles in the milk, this is not best practice, as eventually you want to be making milk that is so super silky, you don’t need to do that.

Step 10. Mix the milk to ensure that the foam is evenly distributed in the pitcher, then pour into your cup or latte glass. Try this for a richer, sweet cappuccino; dust the shot of espresso then pour your textured milk on top of the slightly melted drinking chocolate powder.

Rhino Coffee Gear Professional Milk Thermometers are a hard wearing and reliable device, great for a busy café.
Like any analog thermometer though, from time to time they need calibration. Normally we would suggest checking the accuracy every few months, but depending on the volume of your operations you may opt to check accuracy more frequently.

If your thermometer has been subjected to any heavy handling or abuse (thrown onto a bench or dropped on the floor), immediate recalibration is essential.

During the calibration process it is always preferable to check a couple of different temperatures, for example- 167°F/75°C, 104°F/40°C and 50°F/10°C (or thereabouts).

Cold water can be added to the glass of near boiling water for a faster temperature change. This process will ensure that the thermometer is reading accurately across the full temperature scale.
Remember to allow 60-90 seconds for the temperature to stabilize before you compare readings.
How to: Calibrate using the ‘Ice Bath’ method: Place crushed ice into a glass or milk pitcher, add cold water until you have a slushy consistency. Once the consistency is correct, stir the ice and water mix for 30-45sec and then let it sit for a further 2-3 minutes so the temperature can stabilize.

How to: Calibrate using ‘Boiling Water’ method: Bring a container of water to the boil and use this as a guide for the 212°F/100°C mark. If using the water from your coffee machine boiler please note that hot water is not dispersed at boiling point (212°F/100°C). Refrain from using this as a guide.
 
How to now recalibrate the needle on the dial is out:
- Locate the nut at the top of the thermometer stem
- While holding onto the dial/face, lock a spanner onto the recalibration nut at the rear of the dial
- To increase the temperature, turn the recalibration nut in a clockwise direction
- To decrease the temperature, turn the recalibration nut in a counter clockwise direction
This adjustment may take a couple of attempts to get the needle in the ‘perfect’ position, however the ability to recalibrate provides an essential key to prolonging the life of your analog thermometer.
When you are ready to calibrate using the Ice Bath or Boiling Water method, insert the thermometer into the boiling or ice water and adjust temperature readings accordingly using the adjustment method (explained above).

If preferred you can use both methods and transfer thermometer from the ice water to the boiling water (and/or vice versa). Align the needle to 212°F/100°C if you are using boiling water, or to 32°F/0°C if you are using freezing water.