Publications

uc davis coffee center research publications

Here are some highlights of the coffee research at UC Davis that has been published across multiple fields:

Effect of Basket Geometry on the Sensory Quality and Consumer Acceptance of Drip Brewed Coffee

Journal of Food Science Effect of Basket Geometry

In this work, discrimination tests, descriptive analysis, consumer tests, and total dissolved solids (TDS) were used to evaluate the effects of brew basket geometry on the sensory quality and consumer acceptance of drip brewed coffee. Two basic geometries, semi‐conical and flat‐bottom, were evaluated in conjunction with coffee roast and particle size. Initial discrimination tests showed that small differences in median particle size were not discernable, but that coffees brewed using either semi‐conical or flat‐bottom filter baskets were significantly different (P < 0.05, N = 45). Additionally, coffee brewed in the semi‐conical basket had significantly higher %TDS, and we estimated a sensory difference threshold of 0.24 %TDS. A subsequent descriptive analysis (DA) showed significant differences by roast for 11 attributes and by grind for six attributes. Although brewing geometry, as a single factor, was only significantly different for three independent attributes (smoke aromasweetness, and tobacco flavor), roast × geometry interactions were significant for six attributes (berry flavorbitternessburnt wood/ashcitrus flavorearthy flavor, and sourness) and the grind × geometry interaction was significant for two attributes (bitterness and floral aroma). Attributes showing significant interactions with brewing geometry were also key drivers of consumer liking/disliking. Overall consumer liking (9‐point hedonic scale) was analyzed by cluster analysis (N = 85), which revealed four distinct preference clusters. For each cluster, a particular basket geometry and/or roast level showed lesser acceptance. Overall, the results strongly corroborate the hypothesis that basket geometry affects the sensory quality of drip brewed coffee.

Genetic diversity and re-classification of coffee (Coffea canephora Pierre ex A. Froehner) from South Western Nigeria through genotyping-by-sequencing-single nucleotide polymorphism analysis

Genetic Diversity and re-classification of Coffee canephora

Coffea canephora is an important economic crop in Nigeria, however, little is known about the diversity inherent within, and the genetic relationship among coffee grown and conserved in the country. We examined the genetic diversity and relatedness among 48 Coffea genotypes which included: (a) C. arabicaC. abeokutaeC. liberica, and C. stenophylla, (b) 14 C. canephora accessions conserved in the germplasm of Cocoa Research Institute of Nigeria (CRIN), and (c) 30 farmer-cultivated genotypes collected from South-Western Nigeria. By analyzing 433048 single nucleotide polymorphisms (SNPs) identified through genotyping-by-sequencing we discovered that previous characterizations of C. canephora based on morphological data were inconclusive. Here, we established the correct number of C. canephora varieties present in the CRIN genebank which was four and not six as previously described based on morphological characters. We found three distinct diversity structures within the C. canephora genepool that were dominated by a single genetic group determined from passport descriptors to most likely be of Congolese (Democratic Republic of Congo) origin. High uniformity was also found among the farmer-cultivated accessions with 99% of them representing C. canephora var. Niaouli as their ancestral background. The analysis showed that the genetic base of coffee germplasm in Nigeria is narrow compared to the large genetic diversity of C. canephora. Therefore, broadening this genetic base through future acquisition and hybridization is imperative. However, the relatively high genetic differentiation (FST estimate = 0.3037) identified between Java Robusta and Niaouli will be used as a starting point for our breeding program.

Coffee with co-workers: role of caffeine on evaluations of the self and others in group settings

Coffee with co-workers: role of caffeine on evaluations of the self and others in group settings

This research explores the effect of consuming a moderate amount of commercially available caffeinated coffee on an individual’s self-evaluated participation in a group activity and subsequent evaluations of the experience. Across two studies, results show that consuming a moderate amount of caffeinated coffee prior to indulging in a group activity enhances an individual’s task-relevant participation in the group activity. In addition, subjective evaluations of the participation of other group members and oneself are also positively influenced. Finally, the positive impact of consuming a moderate amount of caffeinated coffee on the evaluation of participation of other group members and oneself is moderated by a sense of an increased level of alertness.

Coffee response to nitrogen and soil water content during the early growth stage

Coffee response to nitrogen and soil water content during the early growth stage

Coffee (Coffea arabica L.) is the major crop grown in highland and mountainous areas of Colombia, where the most common yield‐limiting factors are nitrogen (N) and soil water content. Since the eventual success of a plantation is determined by the performance of coffee plants during critical early stages, our goal was to better understand plant response to these limiting factors. Four different levels of N and soil water content were evaluated under greenhouse conditions for their effect on growth, water use efficiency, fertilizer‐N recovery efficiency (FNRE), and stem lignin and cellulose of coffee seedlings.

The interaction between N and moisture did not produce a significant response in coffee growth. However, by increasing N, both water use efficiency and 13C content were enhanced, while growth, recovery of urea by plants, and stem strength were decreased. Water stress due to low soil water content increased water use efficiency, 13C content, and root to shoot ratio, but decreased shoot growth.

These results demonstrate the effects of N supply and water balance and highlight the excessive amount of N typically applied to coffee seedlings as well as the importance of the acclimation process of young plants to changes in soil N and water. All of these are important considerations in improving management strategies to reduce environmental impact while sustaining optimal productivity.

Evaluating the effect of shade trees on provision of ecosystem services in intensively managed coffee plantations

Evaluating the effect of shade trees on provision of ecosystem services in intensively managed coffee plantations

Intensively managed cropping systems with emphasis on productivity of the main crop can benefit from additional ecosystem services brought by integration of trees in the system − but potential drawbacks must also be accounted for. In an on-farm study, we used a variety of plant, soil and water- related variables to assess the effect of Erythrina spp. and Musa spp. on the provision of ecosystem services in productive, high-quality Coffea arabica plantations in Costa Rica. We found 1) no significant effect of shade trees on coffee production overall; 2) evidence that shade trees do affect flowering and subsequent cherry development, with effects strongly dependent on climate and annual variations in coffee plant physiology; 3) Erythrina shade trees significantly increased soil litter and relative infiltration rate of water in the soil, both linked to soil conservation and decrease in erosion; 4) even in highly fertilized environments, Erythrina trees do fix N which was taken up by adjacent coffee plants. The lack of significant negative effect of shade trees on overall coffee yield and the observation of the provision of other useful services was not unexpected, because of 1) the low density of shade trees in the study site (100–350 trees/ha pruned twice a year on average) and 2) the sensitivity of coffee yields to other interacting effects such as climate, pests and diseases and physiological variations in the plant. Pending further long-term research into the factors affecting coffee yield, we find shade trees provide sufficient ecosystem services to justify their integration in even intensively managed plantations.

Using Single Free Sorting and Multivariate Exploratory Methods to Design a New Coffee Taster's Flavor Wheel

Using Single Free Sorting and Multivariate Exploratory Methods to Design a New Coffee Taster's Flavor Wheel

The original Coffee Taster's Flavor Wheel was developed by the Specialty Coffee Assn. of America over 20 y ago, and needed an innovative revision. This study used a novel application of traditional sensory and statistical methods in order to reorganize the new coffee Sensory Lexicon developed by World Coffee Research and Kansas State Univ. into scientifically valid clusters and levels to prepare a new, updated flavor wheel. Seventy‐two experts participated in a modified online rapid free sorting activity (no tasting) to sort flavor attributes of the lexicon. The data from all participants were compiled and agglomeration hierarchical clustering was used to determine the clusters and levels of the flavor attributes, while multidimensional scaling was used to determine the positioning of the clusters around the Coffee Taster's Flavor Wheel. This resulted in a new flavor wheel for the coffee industry.

Coffee response to nitrogen and soil water content during the early growth stage

Coffee response to nitrogen and soil water content during the early growth stage

Coffee (Coffea arabica L.) is the major crop grown in highland and mountainous areas of Colombia, where the most common yield‐limiting factors are nitrogen (N) and soil water content. Since the eventual success of a plantation is determined by the performance of coffee plants during critical early stages, our goal was to better understand plant response to these limiting factors. Four different levels of N and soil water content were evaluated under greenhouse conditions for their effect on growth, water use efficiency, fertilizer‐N recovery efficiency (FNRE), and stem lignin and cellulose of coffee seedlings.

The interaction between N and moisture did not produce a significant response in coffee growth. However, by increasing N, both water use efficiency and 13C content were enhanced, while growth, recovery of urea by plants, and stem strength were decreased. Water stress due to low soil water content increased water use efficiency, 13C content, and root to shoot ratio, but decreased shoot growth.

These results demonstrate the effects of N supply and water balance and highlight the excessive amount of N typically applied to coffee seedlings as well as the importance of the acclimation process of young plants to changes in soil N and water. All of these are important considerations in improving management strategies to reduce environmental impact while sustaining optimal productivity.

Effects of solution pH, temperature, nitrate/ammonium ratios, and inhibitors on ammonium and nitrate uptake by Arabica coffee in short‐term solution culture

Effects of solution pH, temperature, nitrate/ammonium ratios, and inhibitors on ammonium and nitrate uptake by Arabica coffee in short‐term solution culture

Solution pH, temperature, nitrate (NO3 ‐)/yammonium (NH4 +) ratios, and inhibitors effects on the NO3 ‐ and NH4 + uptake rates of coffee (Coffea arabica L.) roots were investigated in short‐term solution culture. At intermediate pH values (4.25 to 5.75) typical of coffee soils, NH4 + and NO3 ‐ uptake rates were similar and nearly independent of pH. Nitrate uptake varied more with temperature than did ammonium. Nitrate uptake increased from 0.05 to 1.01 μmol g‐1 FWh‐1 between 4 and 16°C, and increased three‐fold between 16 to 22°C. Between 4 to 22°C, NH4 + uptake rate increased more gradually from 1.00 to 3.25 μmol g‐1 FW h‐1. In the 22–40°C temperature range, NH4 + and NO3 ‐ uptake rates were similar (averaging 3.65 and 3.56 umol g‐1 FW h‐1, respectively). At concentrations ranging from 0.5 to 3 mM, NO3 ‐ did not influence NH4 + uptake rate. However, NO3 ‐ uptake was significantly reduced when NH4 + was present at 3 mM concentration. Most importantly, total uptake (NO3 ‐+NH4 +) at any NO3 ‐/NH4 + ratio was higher than that of plants fed solely with either NH4 + or NO4 ‐. Anaerobic conditions reduced NO3 ‐ and NH4 + uptake rate by 50 and 30%, respectively, whereas dinitrophenol almost completely inhibited both NH4 + and NO3 ‐ uptake. These results suggest that Arabica coffee is well adapted to acidic soil conditions and can utilize the seasonally prevalent forms of inorganic N. These observations can help optimizing coffee N nutrition by recommending cultural practices maintaining roots in the temperature range optimum for both NH4 + and NO3 ‐ uptake, and by advising N fertilization resulting in a balanced soil inorganic N availability.

At What Temperatures Do Consumers Like to Drink Coffee?: Mixing Methods

At What Temperatures Do Consumers Like to Drink Coffee?: Mixing MethodsThree hundred consumers were required to mix a hot and a cooler coffee together until it was at a desired temperature for drinking. They added creamer and sweetener to taste. In a 2nd experiment, 108 consumers performed the same experiment with black coffee only, but repeated it using different coffee strengths. In all experiments, the chosen mean preferred temperature for drinking was around 60 °C (140 °F). Black coffee drinkers chose a slightly higher mean temperature than drinkers with added creamer, and they also chose a slightly lower mean temperature when the flavor was stronger. In all cases, consumers tended to choose, on average, temperatures for drinking coffee that were above the oral pain threshold and the burn damage threshold.

Analysis of volatile components isolated from Hawaiian green coffee beans (Coffea arabica L.)

https://onlinelibrary.wiley.com/doi/abs/10.1002/ffj.1067Volatile components isolated from Hawaiian green coffee beans (Coffea arabica L.) were identified by gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS). The mass of total volatile components recovered from 200 g C. arabica beans was 2.7 ± 0.3 mg. The volatile components identified in this extract were: ten alcohols, four aldehydes, one ketone, one lactone, three heterocyclic compounds, two hydrocarbons, and two miscellaneous compounds. The major constituents were 3‐methyl butanoic acid (32.8%), phenyl ethyl alcohol (17.3%), hexanol (7.2%), 4‐hydroxy‐3‐methylacetophenone (3.7%), and 3‐methyl butanol (3.6%). Heterocyclic compounds, important components in providing coffee with their characteristic flavours, were not found in the extract from green coffee beans, except for 2‐methoxy‐3‐(2‐methylpropyl)‐pyrazine.