Can the Brix level of coffee cherries determine the harvest time?

Two clusters of coffee cherries turning red do not necessarily indicate the same level of physiological maturity. Skin color helps harvesters identify the fruit's development stage, but visual observation alone is sometimes insufficient to monitor internal changes in the raw material.

This is why Brix has been included in several studies on coffee ripeness. With just a handheld refractometer, producers can obtain the total soluble solids index in the cherry pulp. However, an important question needs clarification: Does a high Brix reading mean the coffee bean has accumulated more sugars and will definitely produce a better cup quality?

What does °Brix actually measure?

Brix is a common index used to express total soluble solids content, based on the relationship between the refractive index or specific gravity of a solution and a standard sucrose solution. In a solution consisting only of water and sucrose, 1 °Bx corresponds to approximately 1% sucrose by mass.

However, juice extracted from coffee cherries is not a pure sucrose solution. It may contain various soluble sugars, organic acids, mineral salts, and other compounds. Therefore, readings from a refractometer should be understood as total soluble solids values expressed on the sucrose scale, rather than a direct measurement of sucrose content in the coffee bean.

This distinction is crucial. If a batch of cherries measures 16 °Bx, it does not mean the coffee beans inside contain 16% sucrose. These two measurements pertain to different sample types and reflect different chemical characteristics.

What Brix range was recorded for ripe cherries in a 2026 study?

The study titled Optimization of Cibunar Linggarjati Arabica Coffee Quality: Brix Level Analysis and Postharvest Techniques, published on 06/04/2026 in the journal Managing Agricultural Practice and Community Engagement by IPB University, examined two Arabica varieties: Sigararutang and Yellow Caturra.

The research team conducted observations over six weeks on a total of 14 coffee trees. According to the published results:

These results indicate that measuring total soluble solids can help distinguish groups of cherries at different maturity stages under specific research conditions.

However, there is a limitation that cannot be overlooked: the study surveyed only 14 trees of two Arabica varieties at a single location. The 12–20 °Bx range cannot be considered a general harvest standard for all Arabica, nor can it be directly applied to Vietnamese Robusta.

Variety, climate, water regime, crop load, and growth conditions can all alter the rate of soluble solid accumulation. A suitable threshold for Cibunar Linggarjati may not be appropriate for a coffee farm in Lâm Đồng or Đắk Lắk.

A more notable point: sugars in the cherry skin are not identical to sugars in the bean

A study published in Plants in 2024 investigated changes in soluble sugars across different parts of the Arabica cherry.

The researchers classified ripe cherries into six redness levels based on colorimetric measurements, then analyzed total sugars, sucrose, and starch in three components: the cherry skin, skin pulp juice, and the coffee bean.

The results showed that soluble sugar levels change during maturation, but changes in the skin do not fully reflect changes in the endosperm. The study also found no evidence that sucrose and reducing sugars from the red skin layer transfer directly into the bean in a manner that could be inferred from skin color.

This helps explain why the Brix value of fruit pulp cannot serve as a direct proxy for the sucrose content of green beans. Coffee cherries are complex biological systems with distinct tissues and metabolic processes; different parts do not necessarily accumulate nutrients at the same rate.

Color, hardness, and Brix should be interpreted together.

In practice, growers often assess ripeness based on skin color. This method is convenient, rapid, and scalable. However, color can be influenced by variety, weather conditions, pests and diseases, and the physiological status of the fruit.

Brix provides another perspective: the level of total soluble solids in the fruit pulp. Fruit hardness or puncture resistance reflects changes in tissue structure as the fruit matures.

A study classifying seven maturity stages of coffee cherries, published in Coffee Science, compared various methods including color measurement, hardness, soluble solids, moisture content, and dielectric spectroscopy. In that study, color measurement achieved a classification accuracy of 75.1%, hardness 72.5%, while moisture content reached only 45.5% and the dielectric method 56.8%.

These results do not prove that one measurement is inherently superior to all others. They indicate that identifying maturity stages is a multivariate problem, with each indicator providing only partial information.

Do green, yellow-green, and ripe cherries necessarily require the same processing?

A study on wet-processed Arabica in Brazil compared fully ripe cherry lots with "green-cane" lots—cherries that had begun transitioning from green to yellow but were not yet fully red.

The research team used seven batches of raw material, separated the fruit components, processed them via the wet method, and dried them to approximately 11% moisture. The results showed that green beans from green-cane cherries accumulated over 90% of the dry matter found in beans from fully ripe cherries.

Notably, the final cup quality scores did not differ statistically between the two groups when processed separately. However, the cherry group exhibited higher sweetness scores, while the green-cane group displayed more pronounced acidity attributes and higher overall scores within the study sample.

This does not mean green cherries should be harvested to replace ripe ones. It highlights the need to distinguish fully green cherries from green-cane cherries, which have entered the late maturation stage. With appropriate sorting and processing systems, raw material that has not reached full red color can be evaluated and processed separately rather than being blended entirely.

How can refractometers be applied in coffee farms?

Refractometers are better suited for monitoring maturity trends within a single farm rather than using a fixed threshold to determine harvest timing across all areas.

1. Sample separation by variety and location: Do not combine samples from different varieties or plots with differing growing conditions to calculate a general average.
2. Consistent measurement protocol: Use the same method for extracting fruit pulp, the same equipment type, and stable measurement conditions. Refractometers must be zero-checked and the prism cleaned according to the manufacturer's instructions.
3. Simultaneous color recording: Categorize fruits into green, yellow-green, cherry, and overripe groups to correlate Brix readings with visual observations.
4. Temporal repetition: Monitor at multiple points before and during the harvest season to identify increasing, plateauing, or abnormal trends.
5. Correlation with bean quality: After initial processing and sample roasting, compare sensory results with initial Brix data. This approach helps establish reference thresholds specific to each variety and growing region.

The value of Brix lies in its ability to supplement harvest decisions, not to replace comprehensive physiological and quality assessments. When tracked over multiple seasons, this metric can become part of a ripeness management system, enabling growers to make more informed choices regarding harvest timing and raw material sorting.

For coffee, attractive color change is an easily observable signal. However, understanding the extent of fruit maturity requires examining internal changes as well.

For further knowledge on varieties and growing regions, visit SAVINA Coffee Knowledge.

References

1. Hidayat, F. S., Budiarto, T. & Pratama, A. J. (2026). Optimization of Cibunar Linggarjati Arabica Coffee Quality: Brix Level Analysis and Postharvest Techniques. Managing Agricultural Practice and Community Engagement, 1(1), 25–37. https://doi.org/10.29244/mapace.1.1.25-37
2. Baptistella, J. L. C., Assoni, G., da Silva, M. S. & Mazzafera, P. (2024). Variation in Soluble Sugars in Arabica Coffee Cherry Fruits. Plants, 13(13), 1853. https://doi.org/10.3390/plants13131853
3. Velasquez, S. et al. Classification of the maturity stage of coffee cherries using comparative feature and machine learning. Coffee Science. https://doi.org/10.25186/.v16i.1710
4. Dalvi, L. P. et al. (2017). Coffee production through wet process: Ripeness and quality. African Journal of Agricultural Research, 12(36), 2783–2787. https://doi.org/10.5897/AJAR2017.12485
5. USDA Agricultural Marketing Service. Technical Procedures Manual – Brix and soluble solids measurement. USDA Technical Procedures Manual