The quality in coffee, is very much affected by the chemical composition of the green bean, which is directly affected by its pre and post harvest processing conditions (such as variety, climate, soil, altitude, process, storage, etc.). How we measure quality includes: bean size and shape, crop year, number of defective beans, cup quality and moisture, density, water activity.
What is moisture? Moisture content is the amount of water (in the form of vapour) in a sample, given as a percentage of the sample's original weight. In coffee, there is no exact standard for an ideal moisture content, but a generally accepted range goes between 10-12%, with some important exceptions like Sumatra being closer to 12.5%; And Ethiopia and Kenya being closer to 9,5%.
What is density? Density describes how much space a coffee bean takes up (its volume), in relation to the amount of matter in that same coffee bean (its mass). Denser beans are more flavourful, because its cellular development slows down the higher in altitude it's grown (because it’s colder), which means the coffee retains more sugars and nutrients. The farther from the Equator, the lower you need to go to grow high density coffees.
What is Water Activity? The water activity describes the energy state of water in a specific coffee sample, and hence its potential to participate in biochemical reactions and growth of microorganisms (mold, bacteria, etc.). It is used to predict the stability and safety of coffee and food in general, with respect to microbial growth and rates of deteriorative reactions.
What is density? Density describes how much space a coffee bean takes up (its volume), in relation to the amount of matter in that same coffee bean (its mass). Denser beans are more flavourful, because its cellular development slows down the higher in altitude it's grown (because it’s colder), which means the coffee retains more sugars and nutrients. The farther from the Equator, the lower you need to go to grow high density coffees.
What is Water Activity? The water activity describes the energy state of water in a specific coffee sample, and hence its potential to participate in biochemical reactions and growth of microorganisms (mold, bacteria, etc.). It is used to predict the stability and safety of coffee and food in general, with respect to microbial growth and rates of deteriorative reactions.
Flavour is the main and most important criterion for evaluating quality in coffee, so our goal here, is to understand how these three factors will affect your roasting, flavour development and its correlation.
Why are these parameters important when roasting? Basically, because the beans will react in a certain way according to different levels of moisture and density (water activity is directly related to moisture, so for the sake of the roasting part of the article, we’ll just focus on moisture and density) when heat is applied. Let see it more in detail:
Why are these parameters important when roasting? Basically, because the beans will react in a certain way according to different levels of moisture and density (water activity is directly related to moisture, so for the sake of the roasting part of the article, we’ll just focus on moisture and density) when heat is applied. Let see it more in detail:
There are two laws of physics that are worth understanding:
1.- Heat transfer more quickly through denser objects.
2.- Moisture is a great conductor of heat, as it transfers faster in water than in air, for example.
Let’s imagine that we have two 100 ml cylinders, filled up to the top with coffees that have the same moisture content, 10%. Now let’s say that one of these coffees is a low altitude washed Arabica from Brazil, and the other a high altitude washed Arabica from Ethiopia. These two coffees have exactly the same moisture content, but the densities are very different, the Ethiopian being denser, will have more water in it than the Brazil.
It is important to understands that the correlation of these two parameters (moisture and density) will tell us how to better approach roasting a coffee. Moisture content alone is useful for understanding and predicting a series of events throughout the coffee production chain, but for roasting alone, density is the first and main information you should get.
This is a complex topic that deserved a longer article, more discussions and more research no doubt.
1.- Heat transfer more quickly through denser objects.
2.- Moisture is a great conductor of heat, as it transfers faster in water than in air, for example.
Let’s imagine that we have two 100 ml cylinders, filled up to the top with coffees that have the same moisture content, 10%. Now let’s say that one of these coffees is a low altitude washed Arabica from Brazil, and the other a high altitude washed Arabica from Ethiopia. These two coffees have exactly the same moisture content, but the densities are very different, the Ethiopian being denser, will have more water in it than the Brazil.
It is important to understands that the correlation of these two parameters (moisture and density) will tell us how to better approach roasting a coffee. Moisture content alone is useful for understanding and predicting a series of events throughout the coffee production chain, but for roasting alone, density is the first and main information you should get.
This is a complex topic that deserved a longer article, more discussions and more research no doubt.
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