Tamas' Brewing Guide Part 3: Coffee as a compound & the journey to the 100 point coffee...

Now that we have spent some time examining what it means to be a 100 point coffee and how water and water quality are essential to our journey to the perfect cup, lets dig into the main course. Coffee (and if you missed the last post read it here). Understanding coffee as a compound will prepare us to masterfully extract coffees across all brew methods based on roast and solubility both related to cultivar but more-over post harvest processing. So next time you pickup a bag of a natural process Ethiopia that has been light roasted you can get the most from your purchase. Understanding the solubility differences between processing methods and roasting levels can greatly improve the quality and consistency of your extractions, and ultimately the enjoyment of each coffee.  

First, let's discuss what coffee is. Coffee is a small to medium size flowering shrub native to regions approximately 10 degrees North & South of the equator which is informally known as the coffee belt. Below is an overview of the botanical features, life cycle and morphological attributes of coffee. Many people do not realize that the coffee we drink is a seed from a cherry. So in a way we are drinking fruit juice. Well, not really but fruit seed juice, uh hmm more like; roasted fruit seed extract which doesn't sound nearly as good. 

Botanical overview of Coffee:

1. Taxonomy

• Kingdom: Plantae

• Phylum: Vascular Plant 

• Class: Angiosperms

• Order: Gentianales

• Family: Rubiaceae

• Genus: Coffea

• Main Species:

  • Coffea arabica (Arabica coffee)

  • Coffea canephora (Robusta coffee)

  • Other species: C. liberica, C. excelsa, etc.

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2. Morphology

a. Physical

• A small evergreen tree or shrub.

• Typically grows between 2.5 to 4.5 meters in height when cultivated (can grow taller in the wild).

b. Leaves

• Simple, opposite arrangement.

• Glossy, dark green, elliptical or ovate in shape.

• Wavy edges with prominent veins.

c. Flowers

• Small, white, and fragrant (jasmine-like scent).

• Typically emerge in clusters in the leaf axils.

• Hermaphroditic (contain both stamens and pistils).

• Self-pollinating (C. arabica) or cross-pollinated (C. canephora).

d. Fruit

• Known as a coffee cherry or berry.

• Initially green, turns red, yellow, or orange when ripe (species dependent).

• Typically contains two seeds (the coffee beans), though sometimes only one forms — called a peaberry.

• The seed of the fruit is what is processed and exported for roasting and consumption.

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3. Growth and Development

a. Germination

• Seeds take about 2.5 to 3 months to germinate.

• Slow-growing seedling stage.

b. Vegetative Growth

• Branching is opposite and horizontal.

• Produces orthotropic (vertical) and plagiotropic (horizontal) branches.

c. Flowering and Fruiting

• Flowering is often induced by rainfall or irrigation after a dry period.

• Fruit development takes ~6–11 months depending on the species and conditions.

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4. Ecological Requirements

• Temperature: Optimal 18–24°C for C. arabica, 24–30°C for C. canephora.

• Altitude: C. arabica thrives at 600–2000 meters; C. canephora at lower elevations.

• Rainfall: 1000–2000 mm annually, well-distributed.

• Shade: Often grown under canopy in agroforestry systems.

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5. Reproductive Biology

• Pollination:

  • Arabica is largely self-pollinating.

  • Robusta relies on cross-pollination, often via wind or insects.

• Fruit Maturation:

  • Typically 6–9 months for Arabica; 9–11 months for Robusta.

Coffee as a Compound:

After a brief introduction into the botany of our favorite beverage we will move into exploring coffee as a compound. Before you even start brewing you should consider what the desired result is going to be based on your personal preferences, brew method and the coffee you are using. An example would be a shot of espresso vs. drip or french-press etc. This is why we are looking at this from a chemistry standpoint, and how we can optimize flavor and experience using fundamental chemical principles.

As we have discussed brewing coffee in any form is a basic dissolution reaction where the solute (coffee) dissolves into the solvent (water). At what rate and to what degree this occurs depends on the solubility (whole bean and ground) of the coffee and the composition of the water, the temperature of the water and the duration the coffee is in contact with the water. 

Each coffee at baseline has a different solubility, depending on the species, cultivar, process and then finally the roast.

 A simple breakdown of solubility:

 Coffee Process Solubility:

• Natural / Dry & Anaerobic Processes: Most Soluble

• Semi-Washed / Wet Hulled Processes: Less Soluble 

• Washed Process: Least Soluble 

 Roast Level Solubility:

• Dark Roast: Most Soluble

• Medium Roast: Less Soluble

• Light Roast: Least Soluble

The solubility of each coffee and roast directly impacts how many coffee particles dissolve into the water when brewed. The solubility of the coffee and composition of the water will determine the extraction yield meaning the percent of dissolved coffee in the water after brewing is complete. This should also be considered when choosing your brewing device and grind size. Higher solubility will more easily result in over extraction.

So what does this actually mean for you the consumer? I am glad you asked! Simply put the more soluble the coffee, the more coffee particles will end up in the water both desirable and undesirable. So you will need to adjust your grind size and water temperature accordingly to get consistent extraction yields. This is a great tool to use to be able to easily dial in various different coffees from various roast levels and post harvest processing. This also can and should be used in designing the perfect espresso or blend. Below is a breakdown of solubility of coffee and what we are actually extracting into our morning brew. 

1. General Coffee Solubility

• When brewing coffee, only a portion of the ground coffee is soluble in water.

• About 20–30% of roasted ground coffee is soluble in hot water.

• The rest is insoluble plant material (like cellulose and other fibers).

2. Key Soluble Components

The water extracts many compounds, including:

• Caffeine – higher solubility (approx. 2 g/100 mL at room temp; more in hot water)

• Chlorogenic acids – moderately soluble

• Sugars – partially soluble (but partially caramelized during roasting)

• Melanoidins – soluble products of the Maillard reaction

• Lipids and oils – mostly insoluble or partially emulsified in hot water

3. Temperature Effects

• Solubility increases with temperature. Hot water (198-104F) is typically used to maximize extraction.

• Cold brew uses lower temperatures and longer time to extract a different profile of soluble compounds.

Key Concepts for Extraction:

1. Coffee Solubility / Particle Size (grind level) 

2. Water TDS (total dissolved solids)

3. Water Temp

4. Extraction Time

Aromatics and Chemical Breakdown:

The aroma of coffee is one of the most complex in the food world, consisting of more than 1000 volatile compounds. These compounds arise primarily during the roasting process through chemical reactions such as the Maillard reaction, Strecker degradation, and caramelization. Here is a list of the primary groups that are most perceptible.

1. Furans

• Examples: 2-furfurylthiol, furfural, furfuryl alcohol

• Aroma: Roasted, sweet, burnt / browned sugar, coffee-like

• Origin: Formed via sugar degradation during roasting (reduction of long-chain carbs)

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2. Pyrazines

• Examples: 2-methylpyrazine, 2-ethyl-6-methylpyrazine

• Aroma: Nutty, earthy, roasted, popcorn/ peanut-like

• Origin: Maillard reaction between amino acids and sugars

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3. Phenols

• Examples: Guaiacol, 4-vinylguaiacol

• Aroma: Smoky, spicy, clove-like, herbal 

• Origin: Decomposition of lignin and ferulic acid during roasting

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4. Ketones and Aldehydes

• Examples: Acetoin, diacetyl, 2,3-pentanedione

• Aroma: Buttery, creamy, mildly fruity

• Origin: Degradation of amino acids and sugars (strecker degradation)

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5. Esters

• Examples: Ethyl acetate, methyl formate

• Aroma: Fruity, floral, sweet 

• Origin: Fermentation (in green coffee) and thermal breakdown

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6. Thiols

• Examples: 2-furfurylthiol, 3-mercapto-3-methylbutyl formate

• Aroma: Coffee, roasted, savory

• Origin: Maillard and Strecker reactions; very potent even at low concentrations

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7. Terpenes

• Examples: Linalool (Found in Jasmine), geraniol (found in rose & citrus)

• Aroma: Floral, citrus, sweet

• Origin: Present in green coffee; some survive roasting - leading to floral / citrus notes

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8. Lactones

• Examples: γ-butyrolactone

• Aroma: Creamy, coconut, buttery

• Origin: Lipid degradation

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9. Acids

• Examples: Acetic acid, formic acid, citric, etc.

• Aroma: Vinegary, sharp

• Origin: Breakdown of sugars and fermentation (evident in processed coffees)

Major Changes and Components during the roasting process are show below:

 

Compound Class	Specific Compounds	Function/Notes
Aromatic Volatiles	Aldehydes, ketones, furans, pyrazines, thiols	Responsible for aroma (e.g., 2-furfurylthiol = "coffee smell")
Maillard Reaction Products	Melanoidins, pyrazines, Strecker aldehydes	Brown pigments (melanoidins), flavor development
Degradation Products	Acrolein, acrylamide (trace), CO₂	Some are undesirable (toxins), others influence flavor
Decreased Chlorogenic Acids	~50–90% degraded	Reduced bitterness, antioxidant potential changes
Increased Caffeine Concentration (per gram)	Water loss concentrates caffeine	Caffeine is stable under roasting
Lipid Breakdown Products	Oxidized fatty acids, volatile compounds	Affect aroma and shelf life
Caramelized Sugars	HMF (5-hydroxymethylfurfural), furans	Sweet notes, browning pigments
Trigonelline Breakdown	Nicotinic acid (niacin), N-methylpyridinium	Increases vitamin B3 content

 

 

Now that we understand coffee as a compound and its extremely complex properties we are one step closer to the ultimate brew and the 100 point coffee experience. Continue the journey in Part 4...Brew Boldy - a guide to brewing methods.