Pre- and Postharvest Effects on Coffee Quality

Abstract

Despite increasing global specialty coffee consumption, smallholder growers still lack evidence-based strategies for improved coffee quality. Improving the flavor potential of the coffee beverage can translate into a livable wage for smallholders who produce 70-80% of the global supply yet are resource-constrained. In low-input systems, vulnerable to the effects of climate change, field management and postharvest strategies can provide smallholders access to specialty markets, where quality is prized. Addressing this knowledge gap, our work had three aims: (1) to conduct a systematic literature review synthesizing climate change effects of coffee quality (2) to evaluate the effects of Honduran smallholder farming practices on soil health and coffee quality, and (3) to evaluate the effects of postharvest fermentation and drying trials on Colombian coffee quality. Our systematic review synthesized 73 articles addressing our research question, including 42 articles focused on environmental factors, 20 articles focused on management factors, and 11 articles focused on both. The most compelling evidence suggests that (1) increased altitude is positively associated with sensory attributes, and (2) increased light exposure is negatively associated with sensory attributes. Our on-farm, participatory soil management study in Honduras took place on an established, commercial farm and implemented a field experiment to trial soil-health promoting practices. Highly weathered, acidic (pH < 5), were found to be deficient in multiple plant nutrients, especially zinc. These edaphic limitations translated to zinc foliar deficiency. Zinc deficiency is often implicated in lower coffee beverage quality. Results showed that soil management did have a marked effect on coffee physical and chemical quality. However, consumer tasters could not differentiate between coffees arising from differing soil management strategies. In our postharvest coffee processing study, we compared several treatments of postharvest processes (four variations of washed process, including one wet hulled process, two variations of honey process, two variations of natural process) to improve Colombia Caturra coffee beverage quality. Our O2PLS-DA model for process had a high prediction accuracy (Q2=0.76), excellent fit (R2=0.99), and 100% classification accuracy, indicating a robust and accurate multivariate model, providing a successful method of authenticating coffee due to distinct, odor-active aroma compounds arriving from postharvest differences. Our findings advance the discussion on how postharvest processing alters coffee by identifying postharvest strategies for coffee quality improvements that enable smallholder farmers to participate in specialty markets. This farm-to-cup research fills the knowledge gap between coffee growers and coffee drinkers. Relevant to smallholders, these results uncover evidence-based management strategies to mitigate climate impacts on crop quality.