Kinetics of VOCs released from coffee - Introduction
How fast aroma compounds are lost from the freshly grounded coffee
Imagine this. You went to a very fancy specialty coffee and you want to try something exceptional. You order from the 90+ menu, and wow the prices are skyrocket. But what the hell, you want to try this coffee and you order a double shot. Now the main barista is preparing everything to make the perfect espresso. Took the beans and grinds them. Measure the ground coffee and the amount is a little less than it should be. Took some more beans and grinds them, adding them to the rest. Oh, no, now the weight is higher than needed and he took a spoon to remove little by little until measuring the perfect for the recipe 18.4 grams. Doing so, he is constantly talking about the coffee he is going to prepare – what sort it is, from where it is coming, how it was processed, etc. People from the surrounding tables are starting to look around, from where this aroma is coming from. Most of them have already detected the amazing smell coming from the freshly grounded coffee. The entire place starts to smell amazing because this 90+ coffee is so intense on aromas. And you start to wonder, this is the aroma from my coffee I just paid the staggering amount of money. And now these aromas are leaving the coffee irreversibly and won’t end in my final cup of espresso. With every passing minute more and more volatile organic compounds will leave the grounded coffee beans. How much is left in my coffee? Are there any left? Will this influence the coffee extraction and the aroma of my espresso?
Two-three minutes already passed and now the barista started to prepare the coffee puck. Spinning, tapping, WDT (Weiss Distribution Tool) swirling, declumping, mixing, more tapping, etc. Some could overdo and be carried away with the puck preparation technique. The time passes and the smell of the coffee is now everywhere else, but inside of your coffee. With every second the aromatic compounds are lost, and this barista is still doing the WDT mixing. Oh god, just stop and prepare me the espresso I wanted, because after 10 more minutes the coffee won’t taste the same. Or will it? Don’t get me wrong, puck preparation is very important, but is there a drawback if it took 2-3 or more minutes? Jonathan Gagne has such a video where the entire procedure took him 2.5 min. I’m sure that spending time on the puck preparation will lead to better and more repeatable extraction. But evaporation of Volatile Organic Carbons (VOCs) is also an important aspect of coffee, especially after grinding. With time these aroma compounds will be released from the coffee and at a certain point, there will be a noticeable decrease in aroma and taste. According to Clarke and McRae (1) after grinding the VOCs are less than 1% of the total amount of gasses released from the roasted beans. The total amount by weight of VOCs should be around 0.015%. It is a small number, but losing all of the VOCs will have a huge impact on the beverage taste and aroma.
The same story could be transferred also for all kinds of brewing methods. Nowadays, there are very fancy methods to prepare the coffee prior the contact with water, which can take a significant amount of time. A time, that could be crucial concerning the aroma.
In my previous experiment, I already showed the relation between coffee degassing and extraction efficiency in terms of TDS. If you want, you can check my article HERE. It is called “Coffee degassing after grinding” and it focuses on the relation between coffee degassing and TDS.
In this project, I want to focus on the kinetics of VOCs released from the grounded coffee. I want to see how fast these compounds are lost from the freshly grounded coffee and could this influence the taste and aroma of the final brew.
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