Welcome to The Roast, where we detail the journey of unroasted green coffee through storage, transport, roasting at our facility, and eventually to your door as the brown beans you know. In this first piece, we look at the technical coffee storage challenges that inspired us to rethink our methods.
Heraclitus famously claimed that you can’t step in the same river twice. Maybe the same could be said about coffee roasting—you can never roast the same coffee twice. But you can sure as hell try!
Why can you never roast the same coffee twice? Coffee is so many things—a plant, a stimulant, a ritual; but when you boil it all down, coffee is a seed (OK, we promised puns, so there you go. Never boil your coffee!) And, like all seeds, it is living entity that is constantly changing and adapting to its environment.
Coffee seeds, or beans, are hygroscopic, meaning they actively exchange moisture with the environment around them. Put coffee in a humid place, it will get wetter; put it in an arid place, it will get dryer.
Many of the components that give coffee the flavor we so love are preserved in the cell walls of the endosperm. If the coffee is not stored properly then those reserves will be depleted through processes such as respiration and oxidation. As temperature and relative humidity increase, the rate at which these activities occur also increase, further depleting these reserves and thus decreasing the quality of the coffee.
Depending on a seed’s chemical composition, it will need to be dried to a different moisture content level in order to be safely stored. Simply put, moisture content is the amount of water in the seed and is either calculated in “wet basis” terms, meaning the the amount of water divided by the total weight of the seed (dry matter + water) or “dry basis” terms, meaning the amount of water divided by just the amount of dry matter. While water is necessary for the life of the seed, it can also be a bad hombre, leading to rapid deterioration from mold, fermentation, or a high rate of metabolic activity that consumes the cell reserves. This degradation happens through reduction in sugar levels, and increases the levels of polyphenols, electrical conductivity and potassium leaching, among others (Borém et al, 2008).
Seeds that are oily need to be dried more. Why? Since water and oil don’t easily bind, the water in these seeds is less bound to the seed, and is more available to do its bad hombre activities such as fermentation or mold formation. On the opposite end of the spectrum, starchy seeds can be dried less, since water binds to starch and is therefore less available.
Coffee seeds lie in the middle - not too oily, not too starchy. Empirical evidence suggests that the ideal moisture content to store coffee is 11% wet basis (Corrêa et al. 2003; Afonso Junior et al. 2008). The best way to maintain this is to store the coffee at less than 70% relative humidity at the coldest temperature possible above freezing (Borém et al, 2008).
As Guy Clark sang (and Steve Earle wrote), “they say in Texas the weather is always changing, and one thing change will bring is something new.” Over the years, we have struggled with the changing weather in our efforts to keep constant temperature and humidity. Sometimes the summer heat and humidity have inspired our AC to kick on and maintain a wonderful homeostasis at 65° F and 60% relative humidity. Other times, not. Similarly, a cold winter dry spell many a time has left our humidifiers struggling to keep pace with the dry air.
In the past few months we completely remodeled our green warehouse space. First, we increased its size so that we can bring more coffee in-house at once, thus bringing under our control even more the quality of our coffee. More importantly, we added (lots) more insulation, an oversize AC, and mist-aspersion. We can’t stop the aging process of the seed, but I’ll be damned if we won’t die trying!
We have always been searching for the best packaging to transport and store the coffee. I have had the good fortune of participating in some pioneering studies for coffee packaging (Ribeiro 2011; Ribeiro et al. 2013; Andrade 2017).
Our very first coffee was Daterra’s Pearl Reserve which came to us in vacuum-sealed bags as part of their Penta system. When we started importing ourselves, we used vacuum-sealed and then Grain Pro ® bags. Now we are an early adopter for a new packaging technology that provides high-quality moisture barrier bags at a reduced cost for growers (the same ones referenced above in the photo of the sensory analysis team).
Another recent innovation we have implemented with our Brazilian export partner Sancoffee is the use of high-barrier big bags, a method proven to provide better protection for the coffee.
Growing up in Iowa, the sight of grain silos was common, but nothing I gave much thought to. Yet when completing my masters in Agricultural Engineering, one of my favorite classes was on grain silos—calculating systemic pressure, dimensioning fans, determining when to aerate or not based on relative humidity, external temperature and grain mass temperature... I know, I know, it doesn't sound too interesting, and I’m still not sure how I got from loving coffee for coffee’s sake to applying the Janssen equation to determine wall stress in silos.
But perhaps in this awkward interest I have company. After all, you, dear reader, are still reading :) Let's not think about it too much. As a reward for getting through it, here are Guy Clark and Emmylou Harris singing Steve Earle's Ft. Worth Blues.
Afonso Junior, P.C., F.M. Borém, P.C. Corrêa, and V.C. Siqueira. 2014. “Physical and Thermal Properties of Coffee Fruit and Seeds.” In Handbook of Coffee Post-Harvest Technology, edited by F.M. Borèm, 1sted., 30–47. Norcross: Gin Press.
Andrade, F.T. 2017. “Qualidade Do Café Natural Especial Acondicionado Em Embalagens Impermeáveis E Armazenado No Brasil E No Exterior.” UFLA.
Borém, F.M., E.P. Isquierdo, F.C. Ribeiro, J.T Almeida Neto, and A. Piagentini. 2014. “Coffee Storage, Milling and Sorting.” In Handbook of Coffee Post-Harvest Technology, edited by F.M. Borém, 1sted., 143–72. Norcross: Gin Press.
Corrêa, P. C., P. C. Afonso Júnior, F. S. Silva, and D. M Ribeiro. 2003. “Qualidade Dos Grãos de Café (Coffea Arabica L.) Durante O Armazenamento Em Condições Diversas.” Revista Brasileira de Armazenamento 7: 137–47.
Ribeiro, Fabiana Carmanini. 2013. “Métodos Alternativos Para Armazenamento de Cafés Especiais.” Universidade Federal de Lavras.
Ribeiro, Fabiana Carmanini, Flavio Meira Borem, Gerson Silva Giomo, Renato Ribeiro De Lima, Marcelo Ribeiro Malta, and Luisa Pereira Figueiredo. 2011. “Storage of Green Coffee in Hermetic Packaging Injected with CO2.” Journal of Stored Products Research. doi:10.1016/j.jspr.2011.05.007.