What factors affect the quality of coffee during storage?

In the lab

What factors affect the quality of coffee during storage?

Jean Etchats | 2022-01-11

Analysis and understanding of coffee spoilage: through this article, discover which factors affect the quality of coffee.

Deterioration of the quality of green coffee during storage is a reality. It manifests itself in the whitening of green beans and the loss of organoleptic qualities of the beverage. We have observed that degradation times vary greatly depending on the initial quality of the coffees. The Belco quality protocol allows us to explore and analyse the different parameters related to these degradations. We carried out a statistical correlation analysis on more than 4000 references and 3 harvest years. This analysis showed that moisture and water activity (Aw) are the most correlated physical parameters and the most influential on the variation of taste between the departure of the coffee and the arrival in the storage port.

The standard moisture and water activity levels recommended by the ICO are: 8 to 12.5% and 0.5 to 0.7 Aw. These limits are set for health reasons and are intended to prevent the growth of fungi, moulds and toxins such as ochratoxin A.

- Moisture: percentage of water in the total mass. It is the amount of water.
- Water activity (Aw): Amount of water available to undergo interactions with coffee and external elements (moulds, enzymes, yeasts).

Belco analysis : When the humidity and Aw parameters are high, the coffee loses an average of 1.4 points between the pre-boarding tasting and the arrival. The difference is even more significant for higher quality coffees where the "baggy" and "paper" taste notes cause the coffee to lose up to 6 points (SCA score).

Figure 1: Variation in score between embarkation and arrival as a function of humidity. 
Average performed on all coffees analysed since 2018. Over 4000 references and 2 harvests. 

The graph shows us a significant difference in the variation of scores according to the different humidities. This is due to the proliferation of exogenous agents on the coffee bean. Moulds and yeasts do not grow below 12.5% and 0.7 Aw. These high parameters are however conducive to the presence of enzymatic activities.

Figure 2: Food spoilage and proliferation of exogenous agents as a function of Aw

Some enzymes such as pectinases can therefore grow on the grain and cause great taste losses. Pectinase enzymes attack pectin, the main cell wall component of the cells in the coffee bean. Once the pectin is degraded, the cells are no longer protected from external conditions and the embryo dies.

The results of this research led to the definition of new internal specifications at Belco. The requirements for these parameters have been increased from 12.5 to 11% maximum humidity and 0.65 for water activity. Belco wants to support producers from the Quality department and through the field engineers to identify the ideal drying techniques adapted to the conditions of each drying station.

We have also equipped our field teams with portable hygrometers to measure humidity throughout the drying, storage and transport process.

These actions will not only prevent the presence of toxins, but will also minimise the deterioration of the coffee, reduce our complaints to producers and improve the quality of the coffee supplied to our customers.

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