Performance of novel clonal cacao accessions in Hawaii under sustainable farming conditions

State of the plantation

The oldest part of the plantation (2019 planting) entered maturity in the last year.  The area planted in 2020 was still immature at the time of this report.

It was the first year where we had a sizable harvest of cocoa beans and could estimate the proportion of productive trees on the farm.  In order to evaluate this, we performed a survey in March 2022 based on a representative sample of 66 trees:

• Tree development
  • 76% have pods
  • 6% have more than ten pods (Fig. 1)
  • Only 62% were still flowering at the time of the survey
  • average jorquette height: 3.85 feet
• Mortality: 5.5% were considered to need replanting

Fig.1: Highly productive tree

Genetics 

Unfortunately the clones that were going to be tested were never delivered by USDA so the variety trial that was initially envisioned could not take place.

Agronomy

• Weed control

Weeding continued to be a major concern, due to the high levels of rainfall on our wet side of the island.  As described in previous reports, we have developed a sustainable way to control weeds without the use of herbicides: weeding is done only by mowing.

This results in developing a grassy ground cover throughout the plantation that keeps other weeds down and protects against soil erosion

• Control of stumps

Our plantation was originally a sparse secondary forest, composed of invasive trees (African tulip and Albizia).  After clearing, stumps were left that kept producing shoots interfering with cocoa cultivation.  We were able to reduce regrowth by spreading thick black tarp on some of these areas, thereby limiting the use of herbicides.

• Fertilization and soil pH correction (see table 1)

All trees were fertilized every six months with 100 g of 16:16:16 applied around the perimeter of the tree.

As the soil is slightly acidic, all tree perimeters were limed every six months (3 months offset from fertilization ) with 150 g of Ag10 Dolomite.

• Pest and disease mitigation (see table 1)

Chinese Beetles remained the major pest issue, causing in some cases extensive leaf damage.  We were however able to control infestations by applying soil drenches of imidacloprid. This was only done before pods started maturing on the trees (to prevent systemic movement into the mature beans): all the trees were treated with imidacloprid on 9/11/21, which was the only treatment in 2021. We used 100mg of imidacloprid in 5 oz of water.  The treatment was effective and we did not re-apply since.

We noticed symptoms that were reminiscent of the Black Pod fungal disease (Phytophtora palmivora).  Symptoms remained generally limited and only present on a handful of trees (Fig. 2)

Fig. 2: pod presenting symptoms similar to those of  P. palmivora infected pods

Table 1: treatment schedule

Harvesting

• Volumes

There have only been 2 complete harvests so far. One in December 2021 (800 pods, 180 pounds wet cocoa, 72 pounds dry cocoa) and one in March (575 pods, 153 pounds wet, 61 pounds dry).  A partial harvest is underway (around 150 pounds wet), corresponding to about half of the pods available; the other half is planned in June.

All the pods were harvested on trees in the upper lot that were planted in 2019 – representing around half of the trees in the plantation.  None of the trees planted in the lower lot were ready for harvest.

• Pod and bean characteristics
• Number of beans per pod =41.7
• Wet Weight per bean = 2.5g
• Wet weight of beans per pod 104.25 g
• Dry weight per bean 1.01g
• Each kg of wet beans yields about 404 g of dry beans.

Fig. 3: Pods after harvest

Fermentation and drying

• Background

Fermentation is the process of producing individualized beans that have developed structural and flavor characteristics making them suitable for downstream processing and consumption.  It is an essential step in post-harvest processing, which is a complex, natural process involving a diversity of microbes.  The primary objectives of fermentation are:

• To eliminate the pulp (whitish, sticky, sour sweet)
• To develop flavor precursors
• To kill and preserve the beans (together with drying)
• To yield commercial, fermented beans for further transformation into chocolate or associated products

Fermentation consists of 2 major phases:

• An anaerobic phase, during which sugars are fermented to ethanol by yeasts. Lactic acid bacteria are also active at this stage, which produce lactic acid and other metabolites
• An aerobic phase, during which ethanol is fermented to acetic acid through the action of Acetobacter type bacteria

The two phases are necessary to generate the flavor precursors in the bean. During the second phase, a combination of high temperatures and acidity kill the beans, which releases and activates enzymes that are necessary for the generation of these precursors.

To achieve successful fermentation, it is necessary that cocoa beans are under conditions that allow them to undergo these successive phases.  In addition, beans should be handled in a way that does not give opportunities for off-flavors to develop.  These off-flavors can result from the use of spoiled beans or un/overripe beans, poor fermentation conditions affecting microbial development, contamination during fermentation and/or drying leading to the development of molds.

Drying is also very important for flavor development.  Conditions need to allow effective drying while allowing undesirable volatiles, in particular acetic acid, to evaporate.

• Fermentation conditions

Our challenge, on this first year of harvest, has been to develop a fermentation system allowing us to produce the highest possible quality of cocoa from relatively small harvest volumes.  This can be an issue in Hawaii, especially on the East side of the main island, where rainfall is high, day temperatures can be moderate and night temperatures can fall down to 18-20C.  Low fermentation temperatures can result in incomplete fermentation and rain can compromise drying if precautions are not taken to condition fermenting/drying beans appropriately.

• Development of a fermentation method

We had to find containment for our small bean volumes, which would allow a relatively small mass of wet beans to accumulate sufficient heat during fermentation.  We tested different fermentation containments (see below) but ultimately turned to isothermic coolers (for food and beverages), to provide insulation from decreasing temperatures at night time.

In order to accelerate fermentation and give cocoa less opportunity to develop molds, we also tested the priming of fermentation with cultured yeasts (Forte).

Each fermentation was monitored with thermometers to ensure that temperature progression was satisfactory.

A first experiment was conducted to test different types of containment:

• 5 gallon bucket at ambient temperature
• Cooler (12 gal, 45 l)
• 12x12x12 wooden box

All containment was perforated at the base to allow for drainage of juices

The containers were either covered with a lid of with banana leaves (Fig. 4).  Containers covered with banana leaves developed molds and banana leaves were not used after that point.

Fig. 4: Banana leaves used to cover small fermentation batch

Temperature rose slowly and reached 30C at the earliest after 5d.  This was imputed to the low volume of beans in each containment.  Temperature rose fastest in the cooler, which was selected as the containment of choice for these early fermentations.  Still, fermentation lasted a minimum of 8 days (in the cooler), which exceeds the target of 5-6 days.  Fermentation took longest in the 5-gallon bucket (12 days), whereas it took 10 days in the box

Table 2: evolution of fermentation parameters

A second experiment concentrated on fermentation in chest coolers and inoculation with yeast:

• Wet beans were equally distributed between two 55 quart chest coolers (Fig. 5) that were perforated at the base and slightly tilted to allow juice to drain.
• One chest (#1) was stirred by hand and a thermometer placed inside. The other chest (#2) was seeded with 75 g of Forte yeast in 500 ml of water, stirred by hand then closed with a thermometer inside.

On the second day of fermentation, fermentation #1 remained at 23C, while fermentation #2 already reached a temperature of 29.8C with bubbling and the development of a smell of yeast and alcohol.

On the third day, fermentation #1 remained at 23C with a layer of mold growth developing on the surface. Fermentation #2 remained at 30C (probe in middle of batch) with no obvious growth of mold.

Fermentation was eventually stopped at 5 or 6 days after a phase of bean mixing.

The conclusion was that yeast promoted vigorous anaerobic fermentation, shortened fermentation and reduced mold growth, presumably due to the competition of yeast.

Fig. 5: 12 gallon cooler used in fermentation experiments

Overall conclusions of fermentation experiments:

• Fermentation in small buckets or boxes does not reach sufficient temperatures, presumably due to poor insulation and small bean volumes
• The use of banana leaves promotes mold development at the surface and is to be avoided
• Fermentation in isothermic (cooler) boxes allows for stronger increases in temperature
• Yeast inoculation accelerates fermentation and the initial increase in temperature. Mold growth appears to also be repressed

Drying

To protect drying beans, we constructed a wooden drying platform, which was placed under a transparent plastic cover, leaving openings at each end for air circulation (Fig. 6)

The beans were spread for 1-2 weeks with daily mixing.  Drying was performed until moisture reached 7-8%

Fig. 6: Covered area for bean drying (solar drier)