Tracing Water’s Journey Through Coffee, From Seed to Cup

Of the many interesting elements in the journey of coffee from the seed all the way to our morning cup, perhaps the most interesting is the exploration of water in that journey. I'm not referring to water to "brew with" or a style of fermentation, I'm speaking specifically about the moisture content of the "bean" itself. Much like any other cooking process, the control of the specific water amount in the ingredient is key in each of the processes of growing, fermentation, and roasting. Without the right amount of moisture, coffee would not even be able to be ground in a conventional grinder! Here we will explore moisture at each stage of the Coffee’s Journey.

ROASTING DRIES THE COFFEE

Let's start with the most apt element of this for us brewing the coffee, which is the quality of its roast and how effective the coffee was dried in the process of the roast itself. While there are many more thousands of chemical reactions occuring during the roast process through use of the Maillard Reaction (the browning stage in any cooking process) as well as the change from an Endothermic to Exothermic reaction during First Crack, what is often overlooked is the drying element of coffee roasting.

Simply put, green coffee (the name given to the bean / seed after fermentation and before roasting) has far too much moisture to be ground effectively. You are reducing the moisture of the green coffee from 10-11% to an average of 3-5% after roasting. If you tried grinding green coffee you would quickly ruin the burr set - there is a rubbery quality to the feel of the coffee with the amount of water in the seed. By roasting the coffee you are not only drying out the coffee, you are also creating an opportunity for steam to be released from inside the seed itself. This is the stage known as First Crack. Pressure in the bean increases throughout the roast until First Crack, when the chemical reactions become Exothermic and steam is released. This shares some similarities to popping corn and its cooking process. First Crack, plus the Maillard reaction, is where much of the flavor we know and love about coffee occurs.

These flavor transformations along with the drying occurring throughout the entire roasting process allows the roasted coffee to be assessed in terms of its Solubility - or how extractable and brittle the roasted bean becomes. Those same rubbery green coffee beans, through both their roasting and their reduction of water, can now be broken through the force of just your hand, something impossible in its green state. It can also of course, be safely sent through your grinder. Without controlling for moisture in roasting, the beverage we know and love today as "coffee" would not be possible.

Coffee Roasting at Bar Nine, Culver City (2023)

GREEN COFFEE MOISTURE

Now let's go back one step in this process, to the storage of green coffee by the roaster. If the roaster is lucky, they'll be able to receive the Moisture Percentage report of a given coffee from the producer or importer (as mentioned normally between 10 and 11%), which can help determine the best approach in the roaster. Not surprisingly, coffees that have a higher moisture content require greater energy to reach a desired end result than coffees with lower moisture content. While this seems simple enough, the key for the roaster comes down to how it is stored.

As coffee progresses further off-harvest, it will gradually start to lose some of its moisture. Over time, this will impact its taste. Somewhat counter-intuitively, when this happens the roaster will often approach new batches of the same coffee with more energy, as some of the flavor of the coffee will start to mellow and dissipate with age. Much of this has to do with another variable - the coffee's Rate of Rise going into the First Crack stage - although that is its own rabbit hole of conversation which we will come back to at a later time.

A Look at a Roast Curve documenting Rate of Rise using the Cropster Roast-Logging Software

The better the storage conditions, the longer the coffee will retain its moisture. In controlled settings, the roaster will be looking for consistent humidity, temperature, and exposure to natural light. Less light and cooler temperatures are your friend here, as well as protective packaging that creates an air-gap between the green coffee and its environment. Oxygen will rapidly age the coffee and is to be avoided at all costs. On the cooler temperature side of things, some roasters have even experimented and released lots of frozen "vintages" sold years after the fact, like George Howell did with the wonderful Borboya from Yirgacheffe, Ethiopia. Borboya, a Washed coffee of heirloom varieties, retained its moisture by being frozen - leading to vibrant batches roasted years later.

Green Coffee, Ready to Roast

THE FERMENTATION PROCESS

Now let's go back even further and take a look at the Fermentation Process used to dry the coffees at origin. This drying process is crucial to help coffee taste beautiful as well as stay relatively non-Perishable compared to most other seasonal foods, much in the same way cacao is produced. The chemical composition of the coffee changes during fermentation, as its natural sugars are metabolized and its moisture is reduced in controlled ways.

Different fermentation styles will result in different moisture contents. Washed coffees will have a moisture content of 11-12% after fermentation and before drying the seeds, in which the drying will take them down to 10-11%. Natural processed coffees, being dried with the fruit, will reach that same moisture range in one go - combining fermentation and drying. There are also hybrid processes known as either Honey or Pulped Naturals, along with a wide variety of more experimental fermentations such as Anaerobic processing, Carbonic Maceration, and Lactic fermentation. Each of these presents a new world of taste, as well as varying impacts on the level of moisture in the finished green coffee.

A Look at a Natural Process, where the Seed is Dried inside the Fruit to 10-11% Moisture.

Much as in green coffee storage, the level of control the producer has over the fermentation stage will lead to better and more consistent results. This is vital for high quality coffee production, as it takes many of these seeds just to make 1 cup of coffee for our morning brew. If the coffee was fermented and dried in an uneven way, it would lead to inconsistency in both the roasting and brewing of the coffee, with a discrepancy in a given seed's percentage of water retained.

ALL THE WAY BACK TO THE EARTH

We'll end our journey where the coffee's began - in the soil. Nutrient rich soil and well controlled farming practices lead to better coffee cherries. As these become riper, much like in all fruits, the coffee cherry increases in Water content until it is perfectly ripe and delicious. It is at this vital step the picker will hand-pick (many varieties of coffee will reach a ruby red color here). At this stage, the Water in the coffee seed is substantially high, at a whopping 45-55%!

Like every other fruit, if the cherry stays on the tree past this optimal ripeness stage, it will become more and more dense with water. This increase in water while exposed to oxygen rapidly increases the rate at which the coffee cherry can become over-ripe. Picking at the right moisture content is truly key to a great result, as well as in the best tasting seed, factoring in its drying and roasting.

Ripe Coffee Cherries in the Wild. A Seed Inside will have a Moisture Content of 45-55%.

CONCLUSION: A DEEPER APPRECIATION

I love considering how this singular variable can be so essential to everything we know and love about coffee. All of these many steps bring us to our present morning, ready to brew our first cup. Diving within the prisms of farming, picking, fermentation, or roasting, we can see how Water within the seed is perhaps the single most important through-point, and how much the amount of Water dramatically changes along the supply chain, from as high as 55% when picked to as little as 3% after roasting. Beyond coffee, this principle can be applied to cooking, baking, dehydrating, or any other food preparation applied to essentially every ingredient. The specific amount of desired Water in the ingredient is in essence what most all cooking processes, etc are really about.

So let’s drink to Water. It is the foundation of Life as we know it, which also means it is why we have Coffee. Now that is something to celebrate.