This may sound very boring, but it plays an important role in coffee roasting and when it ends up at your coffee shop it will matter. Quality of the taste is affected by the moisture content of the coffee bean. When a coffee plant is harvested and unprocessed it will contain about 50% moisture after it’s picked. Once processed and dried the moisture will drop to around 10% moisture content. Specialty coffees aim for 10%-12% moisture content which generally takes about 15-20 days to achieve. Don’t be confused by higher moisture percentages to produce the better cup of coffee rather as a benchmark for specialty coffee to measure the optimal balance of acidity, aroma, and cupping scores. The main thing is to stabilize humidity so the moisture can remain steady until roasted. At Banyan Coffee, we aim to keep our facility at a constant room temperature and humidity in order to retain a stable coffee bean moisture. Ideally, we try to keep the temperature between 68 and 72 degree and a relative humidity of 45%-50%. We also store our unroasted coffee in GrainPro bags to protect the coffee from moisture and the outside environment. These green bags provide a barrier that keeps mold and fungus from growing.
Like most agriculture products, coffee plants ripen at different times. For a specialty coffee farmer, they will pick the ripened coffee first and process after at different times. It’s important to not mix different batches because this will result in inconsistency in the beans. If inconsistent coffee moisture is produced the farmer could suffer from the coffee roaster not purchasing again. If you have too much moisture, you can also produce an environment in which mold and fungus can develop in the beans. This will jeopardize the entire bag of coffee. Farmers should never rush the processing, however many will do this in order to get the product to the market. The sooner they get it to market the sooner they can get paid.
Coffee that has been over-dried cannot only hurt the coffee taste but financially cost the farmer an extra bag of beans. The weight of the coffee bag is generally 132lbs or 152lbs. If the farmer over dries the bean the coffee will weigh less per bean therefore, they will have to add more coffee to the bag. For the coffee roaster the coffee will have less flavor and freshness.
Roasting and Moisture
If you compare the same coffee before and after roasting there are differences in color, weight, and size. We did an example to prove our point. (pictured above) On the left we have unroasted coffee at approximately 6. 3 lbs. of green coffee. The after-roasting image is on the right, which are the same coffee beans but just roasted. The roasted coffee on the right is less dense and has expanded. It appears to have more coffee but the weight of the beans is 5lbs. rather than the 6.3lbs. of unroasted coffee. Water inside the bean is dried out during the roasting phase. This causes the coffee to lose mass and change in size. This is a result of the release of carbon dioxide and steam forcing itself out of the bean. The bean enlarges from this force expanding out of the bean. Once the bean is roasted there is usually less than 2% moisture content in the bean. The coffee bean can lose about 20% in weight.
There are a few tools out there that can assist in measuring moisture in coffee roasting. A Thermometric probe is an instrument we use to help guide our progress in the different stages of roasting. The different stages hold clues to the moisture content and temperature in the beans. A Sinar AP moisture analyzer can help as a valuable instrument for measuring your moisture content on your beans. This portable device is easy to use in the field and can measure moisture at any stage of the coffee’s life. Using cupping methods as a tool is overlooked when measuring the content of the coffee. Just by tasting the coffee can tell you a lot. Experienced cuppers can tell if the coffee was processed carefully or not.
There are many factors that go into a cup of coffee and moisture content is one that is never thought of when you are sipping your cup at a coffee shop. Here at Banyan Coffee Co. we not only deliver fresh coffee but keep quality control over our beans. Moisture content doesn’t seem important, but the small things always matter.