The Theory of Relative Humidity \u2013 Part 1 (Excerpts)<\/h2>\n
Observing Physical and Sensory Changes in High- and Low-Moisture Green Coffees Under Different Storage Conditions (excerpts taken from Roast<\/a> Magazine\u2019s May\/June 2025 issue, reprinted with permission) There\u2019s little debate that coffee must be dried prior to milling, shipping and storage. However, individual coffee professionals and organizations may have varying standards, and even industry regulators and trade groups have had a difficult time agreeing on the answer to this question.<\/p>\n Since 2004, the International Coffee Organization has defined allowable export ranges from 8 to 12.5 percent. In 2021, in its fourth edition of The Coffee Guide,<\/em> the International Trade Centre established recommended limits between 11 and 12 percent and cautioned that quality loss occurs with anything under 10 percent. Current Specialty Coffee Association (SCA) language avoids discussion of moisture in favor of an upper limit (0.7) for water activity, but prior to 2017\u2019s merger between the Specialty Coffee Association of America (SCAA) and the Specialty Coffee Association of Europe (SCAE) legacy language did specify ideal moisture ranges. In 2004, the organization defined the ideal range as \u201cbetween 9 and 13 percent.\u201d A revision was published in 2013 dictating \u201cwashed processed coffees should be between 10 [to] 12 [percent] upon import.\u201d Moisture content is tested on arrival at an importer\u2019s quality control facility.<\/p>\n Moisture content and water activity<\/a> may indicate how well drying was performed during the later stages of processing. These metrics are important for the safety and health of consumers of roasted coffee. If either is too high, it can predict potential mold and bacterial growth on the green coffee. For that reason, we record moisture content for preshipment samples<\/a> of green coffee before it ships to the U.S. from overseas in order to make sure green coffee doesn\u2019t go bad during this shipping period.<\/p>\n Water activity is an indicator of microbial, chemical and physical properties. It is used to measure safety and anticipates the potential for a chemical and physical reaction.\u00a0Both moisture content and water activity can signify how a coffee will perform in the roaster as well as its shelf-life stability. There are certain flavors that are associated with aged or past-crop coffees, which may be expedited by moisture loss, high water activities, and other water- and storage-related factors.<\/p>\n Past-crop flavors can reduce cup quality ratings and may taste like paper or cardboard in the cup. International coffee shipping<\/a>, depending on origin and destination, typically takes a month or two, and in some cases (such as we saw during the height of the pandemic) over six months, for a coffee to arrive from an origin port to the purchasing<\/a> country. If processing and drying is not done correctly, this can lead to reduced cup quality. Drying in particular is an important step in preventing these flavors.<\/p>\n We knew from common sense<\/a> and prior experience<\/a> that coffee left exposed to the elements of any environment (as is the case in unlined jute packaging) will change more radically and rapidly than protected coffee (such as in GrainPro, Ecotact or similar packaging). What we weren\u2019t prepared for was for how quickly and dramatically the green coffee responded to its environment. We were also surprised at the medium- to long-term sensory impact of storage, regardless of packaging type.<\/p>\n We chose extraordinary coffees, well outside of \u201cnormal\u201d ranges, to help us understand coffee\u2019s physical makeup and sensory quality over time.<\/p>\n A Sumatran coffee, arriving on March 15, 2024, at 15 percent moisture, dried about 1 percentage point per day for three consecutive days. By the time its dehydration had stabilized, the coffee settled at around 9 percent and remained there from March 29 until the termination of our testing on June 20. The storage room metrics (for both coffees) were stable with relative humidity at roughly 49% and average temperatures around 70 degrees Fahrenheit. The same coffee, stored in Ziploc packaging, held steady above 14 percent moisture until May, when it too began to dry out. By June the moisture content of this coffee was down to 12.6 percent.<\/p>\n A Bolivian coffee, arriving on April 18, 2024, at 8.7 percent moisture, changed more gradually. While the coffee held in Ziploc never surpassed 9.1 percent moisture, the jute-stored beans began to show moisture absorption within a week and peaked at nearly 11 percent by the end of the study in early August.<\/p>\n For both the Sumatran and Bolivian coffees, we compared a total sum of words used for Ziploc versus jute, then compared each packaging type\u2019s early tastings to later ones. In all cases, there\u2019s data of interest to explore.<\/p>\n When comparing the Ziploc-stored coffee to that stored in jute, several differences emerged. Overall, the Ziploc- stored coffee was smoother, sweeter and sourer. Further, cuppers checked boxes for \u201cdry acidity,\u201d \u201cmusty\/earthy,\u201d \u201crough\u201d and \u201cspicy\u201d nearly twice as often for the coffee stored in jute. These descriptors, frequently associated with a negative connotation, may indicate a likely overall preference for the coffee packed in the airtight environment.<\/p>\n The Bolivian coffee showed relatively little \u201cpapery\u201d flavors throughout the course of our cupping, reflecting fewer flavors commonly associated with \u201cpast-crop\u201d coffees than the Sumatra. However, it did provide us with some valuable insights as to the way that absorbed moisture can impact a coffee\u2019s flavor.<\/p>\n Comparing the Ziploc-stored coffee with that held in jute, the Ziploc coffee had higher frequencies of \u201ccocoa,\u201d vanilla,\u201d and \u201csweet acidity\u201d descriptors, and more \u201croasted\u201d (despite its lighter ColorTrack scores).\u201d Cuppers used the \u201csweet\u201d descriptor 22% more frequently for the jute-stored coffee.<\/p>\n Ultimately, our study validated a few best practices<\/a> for roasters and challenged a few other preconceptions. We recommend that when milling is completed and coffee is prepared for shipping, high-quality coffees be stored in relatively stable temperatures and humidities and protected with near-hermetic storage when possible. We also recommend roasters and importers maintain similar storage conditions and preserve the integrity of the green coffee\u2019s packaging (e.g., not using hooks to lift jute bags with interior protective liners). Our cuppers, unsurprisingly, had more favorable flavor notes for coffees roasted as close to their arrival date as possible. No storage type will perfectly preserve cup quality over time.<\/p>\n Usual best practices for perishable goods include a \u201cfirst in, first out\u201d policy, with which we generally concur for shipping or roasting green coffee. Exceptions might include coffees with risky moisture contents or compromised storage conditions, which we\u2019d recommend prioritizing for roasting to ensure the coffee is consumed at its peak quality.<\/p>\n For additional practical takeaways, data insights, and more, check out the original publication<\/a> and the companion data visualizations<\/a>.<\/p>\n <\/p>\n","protected":false},"excerpt":{"rendered":" Article Summary: Royal Coffee\u2019s study examines how green coffee storage conditions and moisture levels affect green coffee\u2019s quality and flavor over time. Two coffees, a high-moisture Sumatra (15%) and a low-moisture Bolivia (8.7%), were stored in jute and Ziploc packaging under stable conditions. Results showed that coffees respond rapidly to environmental humidity: Sumatran coffee dried […]<\/p>\n","protected":false},"author":10,"featured_media":216083,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[1258,5362],"tags":[],"class_list":["post-216079","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-education-resources","category-green-coffee-education"],"acf":[],"_links":{"self":[{"href":"https:\/\/royalcoffee.com\/wp-json\/wp\/v2\/posts\/216079","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/royalcoffee.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/royalcoffee.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/royalcoffee.com\/wp-json\/wp\/v2\/users\/10"}],"replies":[{"embeddable":true,"href":"https:\/\/royalcoffee.com\/wp-json\/wp\/v2\/comments?post=216079"}],"version-history":[{"count":4,"href":"https:\/\/royalcoffee.com\/wp-json\/wp\/v2\/posts\/216079\/revisions"}],"predecessor-version":[{"id":222136,"href":"https:\/\/royalcoffee.com\/wp-json\/wp\/v2\/posts\/216079\/revisions\/222136"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/royalcoffee.com\/wp-json\/wp\/v2\/media\/216083"}],"wp:attachment":[{"href":"https:\/\/royalcoffee.com\/wp-json\/wp\/v2\/media?parent=216079"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/royalcoffee.com\/wp-json\/wp\/v2\/categories?post=216079"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/royalcoffee.com\/wp-json\/wp\/v2\/tags?post=216079"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
\n<\/em>By Chris Kornman and Isabella Vitaliano<\/p>\n
\n<\/em>You can view the full issue here: https:\/\/www.roastmagazine.com\/issues\/129<\/a> and explore the data visualizations for our research here: https:\/\/www.roastmagazine.com\/relativehumidity<\/a><\/p>\nWhat is the right moisture content for green coffee?<\/h2>\n
![\"Isabella](\"https:\/\/cdn.royalcoffee.com\/wp-content\/uploads\/2025\/05\/20143801\/CRN6946-640x427.jpg\")
<\/p>\nOur Experiment<\/h2>\n
Moisture Changes<\/h3>\n
Flavor Changes<\/h3>\n
Sumatra<\/a><\/h4>\n
Bolivia<\/a><\/h4>\n
![\"chart](\"https:\/\/cdn.royalcoffee.com\/wp-content\/uploads\/2025\/05\/20143841\/bolivia-storage-physical-data-480x480.png\")
<\/p>\nPractical Takeaways for Coffee Professionals<\/h2>\n