an intuitive guide to coffee solubles, extraction and tds - 1
how does coffee get out of the bean ?
humanity has been trying to solve this problem every morning for a thousand years.
nature imprisons thousands of tasty solubles inside of coffee beans, and we want them in our cup.
over time we've learned that pouring hot water onto coffee grounds turns the water into coffee.
sometimes it tastes good, and sometimes it is not so good. why is that?
we will attempt to answer that question by zooming down to the microscopic level inside of a coffee bean and looking to see what happens when coffee grounds and water meet.
when we look at coffee from the cellular level, it is easy to understand how the ratio of water to coffee, time and grind size impact the brewing process. this will help us build a intuitive sense for thinking about concepts like extraction and total dissolved solids ( tds ).
there is no need to fear these abstract concepts or expect a story filled with mundane technical details.
the story we discover is one of an epic prison break where millions of good guys find freedom and the bad guys are left behind bars. and as you might expect, there is a superhero that saves the day.
a look inside the bean...
with a single arabica coffee bean. if we were to think of this coffee bean as a prison, it would have over 4,500,000 cells! now imagine cutting a horizontal slice right through the middle of the bean in the image ( picture 1 ).
this view is looking down at the cross section of a roasted coffee bean that has been cut in half. notice all of the tiny holes in the bean. each one of those holes used to be a living cell when the coffee bean was growing inside of a cherry on a coffee tree.
with a single arabica coffee bean. if we were to think of this coffee bean as a prison, it would have over 4,500,000 cells! now imagine cutting a horizontal slice right through the middle of the bean in the image above…
living cell when the coffee bean was growing inside of a cherry on a coffee tree (picture 2 ).
this view has been magnified 750x with an electron microscope so we can easily see each individual cell. the width of one of these cells is about half the thickness of one of the hairs on your head. (50 - 70 microns)
when the coffee bean is roasted, the cells fill with co2 and h2o gas and expand and, solid fats and sugars melt . trapped within the walls of each cell are solubles that we want to release into our coffee.
"solubles" is the overarching term that is used for the substances in a coffee bean that can be dissolved by water. at the most basic level, brewing coffee is using water as a solvent to dissolve the solubles that are locked in the cells of a coffee bean ( picture 3 ).
solubles come in many different shapes and sizes. the image above describes the four main categories
found in coffee beans and the unique flavor notes each one contributes to the taste of coffee.
fruit acids and caffeine are the easiest to dissolve and are responsible for light and fruity flavor notes.
lipids are the natural fats and oils found in coffee beans. they aren't technically soluble in water but water can still release them from the coffee cell as an emulsion.
brewing methods that use metal filters like french press and espresso allow lipids to pass through into the cup, producing the mouthfeel those methods are known for.
the pores in paper filters are so small that they prevent most lipids from passing through. drip brewing methods like pour over will only contain 1/10th the lipid content compared methods that use a metal filter.
when coffee is roasted, the malliard reaction produces melanoidins that are responsible for the browning color of coffee, both in bean and liquid form.
during the roasting process, coffee bean components undergo structural changes leading to the
formation of melanoidins, which are defined as high molecular weight nitrogenous and brown-colored compounds. as coffee brew is one of the main sources of melanoidins in the human diet, their
health implications are of great interest. in fact, several biological activities, such as antioxidant,
antimicrobial, anticariogenic, anti-inflammatory, antihypertensive, and antiglycative activities, have been attributed to coffee melanoidins ( picture 4 ).
carbohydrates make up 50% of a dry coffee beans total mass yet only some of the carbohydrates are soluble. their main role is to add sweetness and earthy flavors.
as the coffee cherry develops on the tree, mother nature locks these innocent solubles inside the cells of each coffee bean.
we're back inside the coffee bean and it's not looking good for the solubles. after the bean has developed, been picked, processed and roasted the solubles are locked up inside of dark cells ( picture 5 ).
 |
| picture 1 |
nature imprisons thousands of tasty solubles inside of coffee beans, and we want them in our cup.
over time we've learned that pouring hot water onto coffee grounds turns the water into coffee.
sometimes it tastes good, and sometimes it is not so good. why is that?
we will attempt to answer that question by zooming down to the microscopic level inside of a coffee bean and looking to see what happens when coffee grounds and water meet.
when we look at coffee from the cellular level, it is easy to understand how the ratio of water to coffee, time and grind size impact the brewing process. this will help us build a intuitive sense for thinking about concepts like extraction and total dissolved solids ( tds ).
there is no need to fear these abstract concepts or expect a story filled with mundane technical details.
the story we discover is one of an epic prison break where millions of good guys find freedom and the bad guys are left behind bars. and as you might expect, there is a superhero that saves the day.
 |
| picture 2 |
with a single arabica coffee bean. if we were to think of this coffee bean as a prison, it would have over 4,500,000 cells! now imagine cutting a horizontal slice right through the middle of the bean in the image ( picture 1 ).
this view is looking down at the cross section of a roasted coffee bean that has been cut in half. notice all of the tiny holes in the bean. each one of those holes used to be a living cell when the coffee bean was growing inside of a cherry on a coffee tree.
with a single arabica coffee bean. if we were to think of this coffee bean as a prison, it would have over 4,500,000 cells! now imagine cutting a horizontal slice right through the middle of the bean in the image above…
living cell when the coffee bean was growing inside of a cherry on a coffee tree (picture 2 ).
 |
| picture 3 |
when the coffee bean is roasted, the cells fill with co2 and h2o gas and expand and, solid fats and sugars melt . trapped within the walls of each cell are solubles that we want to release into our coffee.
"solubles" is the overarching term that is used for the substances in a coffee bean that can be dissolved by water. at the most basic level, brewing coffee is using water as a solvent to dissolve the solubles that are locked in the cells of a coffee bean ( picture 3 ).
solubles come in many different shapes and sizes. the image above describes the four main categories
 |
| picture 4 |
found in coffee beans and the unique flavor notes each one contributes to the taste of coffee.
fruit acids and caffeine are the easiest to dissolve and are responsible for light and fruity flavor notes.
lipids are the natural fats and oils found in coffee beans. they aren't technically soluble in water but water can still release them from the coffee cell as an emulsion.
brewing methods that use metal filters like french press and espresso allow lipids to pass through into the cup, producing the mouthfeel those methods are known for.
the pores in paper filters are so small that they prevent most lipids from passing through. drip brewing methods like pour over will only contain 1/10th the lipid content compared methods that use a metal filter.
 |
| picture 5 |
during the roasting process, coffee bean components undergo structural changes leading to the
health implications are of great interest. in fact, several biological activities, such as antioxidant,
carbohydrates make up 50% of a dry coffee beans total mass yet only some of the carbohydrates are soluble. their main role is to add sweetness and earthy flavors.
as the coffee cherry develops on the tree, mother nature locks these innocent solubles inside the cells of each coffee bean.
we're back inside the coffee bean and it's not looking good for the solubles. after the bean has developed, been picked, processed and roasted the solubles are locked up inside of dark cells ( picture 5 ).
*note, the colored balls are used as a representation of the solubles and are not drawn to scale.
** from handground.com
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