The ideal harvest point goes beyond color

If you are a coffee grower and work with quality, you have probably already asked yourself: is it time to harvest? How long can I still wait?  

Technically, the harvest should not begin until the coffee trees reach at least 80% ripe fruit. We know that both the yield and the quality of the coffee are directly related to the harvest point and the ripening index of the fruits.

The main evidence of maturation is the change in the color of the skin. In coffee, it transitions from green to red or yellow, depending on the variety. This is the result of the intensification of respiratory activities, production of ethylene and, subsequently, the degradation of chlorophyll and the synthesis of pigments such as carotenoids and anthocyanins.

Although nature is extremely educational, the coffee grower has already realized, in practice, that appearances can be deceiving. Visual color identification may not be an efficient standard for determining fruit ripeness and the ideal harvest time. And this seems to be particularly difficult for some yellow varieties.

In grains originating from unripe fruits, there is a higher concentration of phenols such as tannins, lignins and chlorogenic acids, which are responsible for the astringency of the fruits and, consequently, the drink. Ripe fruits, on the other hand, in addition to greater grain weight, also have a higher content of total titratable acidity, reducing and non-reducing sugars, total sugars and total soluble solids.

The physiological process of maturation involves the metabolism of various grain constituents, it is not a simple phenomenon. Highlighted are volatiles, phenolics, fatty acids, proteins and some enzymes, which vary in presence and content. It is influenced by genetic, climatic and cultural parameters. This combination often creates a scenario of uneven maturation in the field, which becomes a major challenge for the specialty coffee producer.

In their eagerness to resolve the issue, some coffee growers are appealing for a growth regulator from the chemical group ethylene. With the application of ethylene, crops gain a perfect and extremely homogeneous appearance of maturity.

But, in general, the forced maturation process does not go much beyond the exocarp (shell). This makes green and green fruits pulpable, which seems advantageous, as it increases the amount of peeled cherry production through wet processing. In practice, the coffee grower is simply contaminating his perfect batch with beans that will add astringency to the drink. No matter how visually attractive the fruits may appear, this is forced maturation and has a detrimental effect on quality. In fieldwork and scientific literature, nothing is found that justifies the use of ethylene for the production of specialty coffees.

BRIXOMETER

The brixometer or refractometer is an optical instrument that measures the refractive index of a solution mixture. Light, when passing through the liquid, undergoes refraction (change in angle). This change in angle is measured by the device in degrees brix, which is an indirect determination of the soluble solids content. Around 85% of the soluble solids are sugars. Brixometers recommended for coffee can be analog, simpler and cheaper, or digital. The cost of purchasing the equipment can be less than a thousand reais or more than 5 thousand reais, depending on the level of technology used.

In search of natural sweetness

The use of a refractometer or brixometer to estimate the ideal harvest point has become increasingly popular for coffee growing. This is done by reading the soluble solids (brix) values ​​of the juice obtained by manual compression of the ripening fruits.

The soluble solids content represents the content of sugars, mainly glucose, fructose and sucrose, organic acids and other minor constituents. The estimation of these levels, using the brixometer, can be interesting for predicting the quality of the coffee drink. Since sugars react during roasting, they are responsible for the brown color and desirable flavor and aroma characteristics.

Although the effect of sugars on the quality of coffee is known, and the possibility of soluble solids from the pulp migrating and influencing the characteristics of the bean, it is not really known in what proportion. Another hypothesis is that there may be a common trigger that influences, at the same time, the constitution of the coffee pulp and seed. Reading the brix would be an indirect way of estimating what is happening inside the fruit.

The use of brix in coffee farming still has many unknowns and protocol adjustments. The coffee drink originates from the beans and this makes the relationship between quality and brix values ​​restricted. Especially when compared, for example, to agronomic crops such as grapes, sugar cane and citrus, whose final products originate from the juice of the pulp or stalk.

In a scientific study, carried out in the Matas region of Minas Gerais, it was possible to observe that the average brix values ​​during a harvest are increasing throughout the entire period. The graph shows that cherry fruits collected at the beginning of the harvest had average brix values ​​of 20,7, while fruits at the end were 22,8. At these two points, the sensorial quality of the drink was also analyzed and, respectively, the scores were 78,8 and 84,3 according to the Sensory Assessment Methodology of Specialty Coffee Association - SCA.

Another important observation is that cherry fruits have been shown to have a maturation cycle (ripening, peaking and senescence) of approximately five days. This means that, if the coffee grower really wants to use the refractometer effectively, he must monitor it daily to know the ideal harvest time.

In general, brix values ​​for coffee vary from 15 to 30 degrees. However, reference values ​​for quality are not yet properly defined, there are numerous factors that influence the chemical, physical and sensorial characteristics of coffee. However, values ​​above 22 degrees brix have been observed for specialty coffees.

The degree of brix has been continuously used to determine the ripeness and palatability of various agricultural products. They can be a great harvest and post-harvest management tool. But, it never hurts to mention, the brix degree is an estimate of the soluble solids in the fruit pulp. And, studies lead to the conclusion that high values ​​of soluble solids are one of the conditions for specialty coffees, never a guarantee.

More information about the use of brix can be found in the following publication.