Moisture in CoffeeMoisture in CoffeeMoisture in Coffee Equals Quality
(From the grower to the master connoisseur)
Coffee prices are currently at peak levels, even higher than the freeze of '94. Everyone I have spoken with involved in
coffee is in a frienzed state.
Moisture in coffee beans is frequently a last minute item of concern. However, it is a significant factor in the quality and
cost of coffee. Beginning at time of harvest, moisture is a key determinant of the maturity of the bean for harvest. This
maturity has a continuing influence on the quality of the coffee at each of the next steps. It determines the amount of
drying needed to stand the rigors of shipping. It is a principal economic factor due to weight loss of the green beans
during storage and roasting.
Understanding moisture is one of the keys to the art of roasting and allows the maintenance of a consistent roasted product
from batch to batch. It is also a factor in the effectiveness and efficiency of the final step of the grind. Economics,
processing and in the end, the taste of the brewed coffee result is influenced by moisture content in the bean, from green to
roast to ground.
Determining the Ideal Picking Time
In talking with growers from different parts of the world, I have learned that from the time the bean is harvested, moisture
plays an important role. If the bean is not picked when the crop is within the optimum moisture content range, it is at
risk of deterioration from environmental conditions.
For example, the risk of the discoloration of the beans (loss of the green tint and the development of a musty, whitish
color) can be greatly reduced if not eliminated when the harvest is done if the beans are in the optimum moisture range
(20-30 % moisture). Measuring moisture in the fields to control harvest schedules is an important element in this first step
of the process and has implications for subsequent production techniques.
Finding the Optimal Drying Parameters
Growers need to constantly monitor moisture content in order to determine the best drying time and procedures. For example,
green beans in Indonesia will typically be higher in moisture content than green beans in Columbia because of the higher
humidity in Indonesia. Consequently, different drying schedules and techniques may improve the drying results.
Frequently, two loads of green beans from the same region have different moisture contents. This may be the result of
different drying methods or varying weather conditions. For example, three different growers advertise that they use the
gentle drying process. However, the grower in Kenya uses a concrete patio, the grower from Ethiopia is using netting and the
grower from Ghana uses the drying table approach. If the process is not monitored by measuring the beans moisture, wide
variations in the resulting content can be expected.
The variations in the methods used and the differences in weather condition in each of the countries would effect drying
times. Without a means to measure the changing moisture, wide differences would be expected.
Shipping & Storage
Many exporters and importers have informed me that one of the keys to cost effective purchasing is knowing the moisture
levels of the product at the shipping destination. Moisture levels in green coffee at this juncture not only have impact on
processing and taste but are a significant factor in the price.
During shipping, coffee beans are exposed to wide variations of temperature and humidity. These environmental changes often
result in condensation and other exposure to the source of absorbed moisture. Because it is difficult to control these
environmental factors during shipping, obtaining the correct moisture levels at the completion of the drying process is of
paramount importance. If the beans are too dry (below 9 % moisture), beans will immediately begin to lose flavor. If the
beans are too wet (above 13% moisture), they will mold easier.
Aside from the issue of potential deterioration, the moisture at the level contracted for determines observed roast shrinkage
at any given roast.
Get the Best Roast out of Your Bean
During the roasting process, the quality of the beans determines the consistency of the blend and the taste, roast after
roast. Knowing the moisture content of the green beans prior to roasting helps the set up of the roaster.
For example, roasting a Colombian with a moisture content of 9.5% with roaster settings of 400 degrees F for 120 seconds
produces a standard product.
If the next Colombian batch had a moisture content of 12%, the same setting would produce
something different from the standard product. With the knowledge of the new product. With the knowledge of the new batch
moisture content, adjustments in roast time and temperature could be made to again produce the standard product.
Measurement of moisture content is a principal way to shrinkage. The shrinkage tells you what your bottom line is going to
be and more importantly it supports the fact that you are producing a quality product with excess quenching. Knowledge of
shrinkage data provides you with realistic factors for determining efficient cost pricing structures.
The Grinding Process
As with roasting the outcome of the grinding process is dependent on the moisture of the beans. The impact of moisture in
the grinding process is twofold. At high moisture levels the beans will not pass through the grinder uniformly and can cause
a clogging of the grinders. At lower moisture levels, dry grounds can create static electricity problems.
The grind size also affects the extraction rate of the coffee. The perceived taste of the coffee is affected significantly
if your grind-size is larger or smaller than it should be. Even though grind-size seems like a small matter, it is certainly
a big factor when it comes to the perceived quality and taste of your coffee.
The Sinar System
Sinar developed a moisture measuring instrument that is designed to measure moisture in parchment, green coffee, roasted
coffee and ground coffee.
This equipment is being used as a tool to determine optimum harvest time, length of drying, condition of coffee after
shipment, control of roaster settings and help with grinding. It can be used from the fields to the production plant.
