Cacao Post-Harvest Processing
From pod to dried bean: pulp chemistry, Brix, pH, fermentation phases, and drying. What happens at each stage and how to assess it.
Post-harvest processing creates the flavor precursors that roasting converts into chocolate character. Fermentation has two distinct phases, driven by different microbial populations with different chemistry. Drying arrests those reactions and removes moisture to a shelf-stable level. Every step is a process decision with a direct flavor consequence. A raw bean has almost no chocolate flavor potential; a well-processed dried bean has most of it already locked in.
Pod harvest and selection
Cacao pods are harvested by hand, cut from the trunk and main branches with a machete or harvesting hook. Ripe pods change color as they mature: depending on the variety, they shift from green to yellow, red to orange, or purple to red. Ripeness is critical: under-ripe pods contain less sugar in the pulp, which limits fermentation activity and the compounds available to the microbes. Over-ripe pods may have pulp that has already begun to ferment on the tree, disrupting the controlled fermentation that follows.
Pods are typically harvested every two to four weeks during the main crop season. Holding harvested pods for several days before breaking ("pod storage" or "pre-conditioning") is practiced by some producers. A short hold of 3 to 7 days allows endogenous enzymes in the pulp to begin breaking down cell walls and modifying the sugar-acid balance, which can lead to more complete fermentation. It is not universal and is not a substitute for good fermentation management.
Pod breaking and bean extraction
Pods are broken open as soon as possible after harvest or after the pre-conditioning period. Breakage is done by hand or with a wooden mallet, splitting the pod laterally to expose the beans. Metal tools are generally avoided because contact between iron/copper and the polyphenol-rich pulp can cause oxidation reactions that produce off-flavors.
Each pod contains 20 to 50 beans, each surrounded by a white mucilaginous pulp called the testa or mucilage. The beans are scooped out by hand and collected in a central pile or directly into fermentation vessels. The placenta (the central strand connecting the beans inside the pod) is discarded. Speed matters: once pods are opened, the exposed pulp begins oxidizing and microbial activity starts within hours.
Pulp chemistry: Brix and pH
The white pulp surrounding each fresh bean is the feedstock for fermentation. Its composition determines what the microbes have to work with, and therefore what the fermentation can produce.
Fresh pulp is primarily water (80 to 85%), with a sugar fraction dominated by sucrose, glucose, and fructose, and an acid fraction dominated by citric acid. It also contains pectin (which breaks down during fermentation, causing the pulp to liquefy and drain away) and a range of other organic compounds that influence microbial activity.
Brix measures the dissolved solids concentration of a liquid, expressed as grams of sucrose per 100g of solution. In fresh cacao pulp, Brix is primarily a proxy for sugar content. Fresh pulp from fine flavor varieties typically reads 15 to 22 degrees Brix. Lower Brix indicates less available sugar, which limits yeast activity and ethanol production in the anaerobic phase. Higher Brix (above 20) provides more substrate but can inhibit microbes at the extremes.
Measured with a hand refractometer. Place a drop of fresh pulp on the prism, close the cover, and read through the eyepiece. Most refractometers have a direct Brix scale.
Fresh cacao pulp is acidic, typically pH 3.0 to 3.8. The primary acidulant is citric acid, which is also partially responsible for the brightness of certain fine flavor origins (notably Madagascar). This low pH creates a selective environment that initially favors acid-tolerant yeasts over bacteria, establishing the microbial succession of fermentation. pH rises as fermentation progresses and acid is consumed or converted.
Measured with a calibrated pH meter or indicator strips. Strips are less precise but sufficient for field monitoring. Check at the start, after turning, and at the end.
Brix and pH together give a quick read on pulp quality before fermentation begins. Low Brix combined with high pH (less acidic than expected) often indicates over-ripe or poorly stored pods. High Brix with very low pH is characteristic of high-quality fresh pulp from a well-managed harvest. Neither number alone is sufficient: a high-Brix, high-pH lot means the sugars are present but the acid environment that controls early microbial succession is not.
Fermentation overview
Cacao fermentation is a natural, spontaneous process driven by wild microorganisms present on the beans, pods, fermentation vessels, and surrounding environment. It is not inoculated in most traditional production. The succession of microbial populations over 5 to 8 days follows a predictable pattern driven by changes in temperature, oxygen availability, pH, and available substrates: yeasts dominate early, lactic acid bacteria overlap with them, and acetic acid bacteria take over in the later stages as oxygen becomes available.
The fermentation has two broad phases with distinct chemistry and distinct flavor consequences. Both are necessary. Skipping or abbreviating either leaves the bean chemically incomplete: under-fermented cacao lacks the precursors for complex flavor, and poorly managed later-stage fermentation fails to kill the seed and complete the transformation of polyphenols.
Anaerobic phase
Days 1 to 3, yeast-drivenWhen freshly extracted beans are piled together, the mass immediately begins to self-seal: the beans pack tightly, CO2 produced by early microbial activity fills the interstitial space, and oxygen is rapidly consumed. Within a few hours, the interior of the mass is anaerobic. This is the environment that favors Saccharomyces cerevisiae and related wild yeasts, which thrive without oxygen and tolerate the low pH of fresh pulp.
Yeasts ferment the pulp sugars (primarily glucose and fructose after invertase cleaves sucrose) into ethanol and CO2. Ethanol production is rapid in the first 24 to 48 hours. Alongside ethanol, yeasts produce fusel alcohols (isoamyl alcohol, propanol, isobutanol) via the Ehrlich pathway from amino acids, and a range of esters (ethyl acetate, isoamyl acetate, ethyl hexanoate) that directly contribute fruit character to the finished bean. The specific yeast strains present vary by origin and farm, which is part of why the same variety fermented in different locations produces different flavor profiles.
Pectinases produced by yeasts and endogenous bean enzymes break down the pectin network in the pulp, causing it to liquefy progressively over the first two to three days. The liquid (called sweatings) drains away through drainage holes in the fermentation box or out of the heap base. The drainage of sweatings is important: it removes sugar substrate that has been depleted, introduces oxygen to the outer layers, and reduces the total volume and temperature buffering of the mass, which facilitates the phase transition to aerobic conditions.
Rising from ambient. Microbial metabolic activity generates heat. Inner mass warms faster than outer layers.
Relatively stable early. Lactic acid bacteria begin producing lactic acid from day 1, gradually lowering pH further before it rises in the aerobic phase.
Anaerobic conditions essential for yeast dominance. Premature turning before day 2 introduces oxygen too early and disrupts the yeast phase.
Varies by variety, mass size, and ambient temperature. Criollo tends to complete the yeast phase faster due to less pulp and faster drainage.
Lactic acid bacteria (LAB) are active throughout the anaerobic phase alongside the yeasts, producing lactic acid and contributing to the complex microbial ecology. LAB species are generally more tolerant of acidity than acetobacter and serve as a bridge microorganism between the yeast-dominated early phase and the acetobacter-dominated late phase. The ratio of lactic to acetic acid in the finished bean is partly determined by how long the LAB have to work before oxygen introduction accelerates the acetobacter populations.
Aerobic phase
Days 3 to 7, acetobacter-drivenAs pulp drainage continues and the bean mass is turned, oxygen penetrates the mass. This triggers a shift in the dominant microorganism: Acetobacter and related acetic acid bacteria (AAB) require oxygen to function and now have both the oxygen supply and the ethanol substrate to proliferate rapidly. They oxidize ethanol into acetic acid and water in a two-step reaction, releasing a significant amount of heat.
The oxidation of ethanol to acetic acid is exothermic. The internal temperature of the fermenting mass rises from the 35 to 40°C range of the yeast phase to 45 to 50°C or occasionally higher during peak acetobacter activity. This temperature rise has two critical functions: it kills the bean embryo (preventing germination and triggering the cell death that releases flavor precursors from their intracellular compartments), and it activates endogenous enzymes at temperatures where they are maximally effective. A fermentation that never reaches these temperatures is almost always under-fermented in the aerobic phase, regardless of total duration.
The death of the seed embryo is the starting gun for the most important internal chemistry of fermentation. Cell membranes rupture, allowing previously compartmentalized compounds to mix for the first time. Polyphenol oxidase contacts the tannins and begins oxidizing them into larger, less astringent polymers (browning the cotyledon interior from purple to brown). Proteases hydrolyze storage proteins into free amino acids, building the Maillard precursor pool. Invertase cleaves remaining sucrose. Acetic acid diffuses into the bean, lowering internal pH and creating the acidic environment that drives further enzymatic reactions.
Peak during peak acetobacter activity. Temperatures above 55°C begin to inhibit AAB and can produce off-flavors. Temperatures that stay below 42°C throughout suggest inadequate aerobic fermentation.
Rising from the low-pH anaerobic phase as citric acid is consumed and the bean's internal environment is modified by diffusing acetic acid and enzymatic activity.
Physically redistributes the mass, introduces oxygen throughout, normalizes temperature gradients, and prevents the outer layers from over-fermenting while the interior under-ferments.
Total fermentation (both phases) is typically 5 to 8 days for bulk Forastero, 4 to 6 days for Trinitario, and 3 to 5 days for Criollo.
Fermentation methods
The container and format of fermentation affects temperature retention, drainage rate, oxygen access, and how effectively the mass can be turned. Each method has tradeoffs.
Wooden boxes with drainage holes in the base. The most controllable and widely used method for quality-focused production. Boxes are typically constructed from untreated hardwood (softwoods can impart off-flavors). Capacity ranges from 50 kg to several hundred kg per box. Larger boxes retain heat better but require more thorough turning to prevent temperature gradients. Cascading multi-box systems allow beans to be transferred (turned) from one box to another, thoroughly remixing the mass at each turn.
Beans piled on banana leaves on the ground, covered with more leaves or burlap. The traditional method across West Africa and much of Southeast Asia. Lower startup cost. Temperature retention depends heavily on heap size: small heaps lose heat quickly. Less uniform fermentation than box methods due to the temperature and oxygen gradient from surface to interior. Turning a heap is labor-intensive. Produces consistent results at large volumes when managed well, but less precision than box systems.
Wicker baskets or wooden trays used for small-batch artisanal production. Common in island origins (Martinique, some Pacific origins) and micro-farms. Small volume means faster heat loss and more difficulty maintaining temperature in the aerobic phase. Requires close monitoring. Can produce excellent results for small batches where the producer can intervene frequently.
Assessing fermentation: the cut test
The cut test is the standard method for evaluating fermentation completeness. Take a representative sample of 20 to 30 beans from different parts of the mass (top, middle, bottom, different sides of the box). Cut each bean longitudinally through the cotyledon and assess the interior color and texture.
The cotyledon cells are intact, polyphenols have not been oxidized, and no enzymatic transformation has occurred. This bean will taste intensely astringent and bitter with no chocolate potential.
Fermentation has begun but not completed. Some polyphenol oxidation has occurred at the periphery but the interior is still raw. Common when fermentation was too short or temperatures in the aerobic phase were too low.
Polyphenol oxidase has worked throughout the cotyledon. The brown color indicates oxidized tannins. Fissures are caused by cell rupture and enzymatic activity during the aerobic phase. This is the target appearance.
Fermentation extended past the point of chemical benefit. The interior has been consumed or degraded beyond usefulness. Over-fermented beans contribute rancid, acetic, or off-flavors that cannot be corrected downstream.
A well-fermented lot should show at least 80 to 85% fully brown beans in the cut test. 90% and above is excellent. Any lot below 75% brown will produce chocolate with noticeable astringency and bitterness regardless of roast or conching choices. The cut test result is the most important single piece of information about a lot of beans; if a supplier cannot provide it or a photograph of it, treat the lot as unknown quality.
Drying
Drying is not simply moisture removal. It is the final active processing stage, during which residual enzymatic reactions continue in the bean, volatile acids evaporate, and the flavor profile is stabilized. How the beans are dried is as consequential as how they were fermented.
The target moisture content for shelf-stable dried cacao is 6.0 to 7.5%. Above 8% the beans are susceptible to mold during storage and transport. Below 5% the beans become brittle and crack easily during handling, and some aromatic compounds are lost. The target is not simply "dry enough": it is dry enough to be stable while retaining the volatile aromatic compounds that contribute to fine flavor.
The preferred method for fine flavor production. Beans are spread in a single layer on raised bamboo or wood-slatted beds that allow airflow beneath the mass. Raised beds keep beans away from soil microbes, reduce contamination risk, and allow more even drying through air movement from below as well as above. Drying takes 5 to 10 days depending on sun intensity, ambient humidity, and bean load.
Gentle, allows continued slow enzymatic activity. Preserves aromatic complexity. Produces the cleanest sensory profile.
Weather-dependent. Rain interruptions can lead to mold if beans rewet significantly. Labor-intensive (requires raking every few hours).
Beans spread on concrete or clay patios. Widely practiced in West Africa and Latin America. Lower infrastructure cost than raised beds but greater contamination risk from soil contact, and less airflow from below. Patio temperature can become very high in direct sun, which can case-harden beans (the outer layer dries faster than the interior, trapping moisture).
Low infrastructure cost. Effective at scale.
Risk of case hardening and mold if improperly managed. Potential soil contamination. Uneven drying without constant raking.
Forced hot air through rotating drums or trays. Used primarily when weather is unreliable or production volumes require throughput that sun drying cannot match. Temperature control is critical: drying air above 50 to 55°C produces case hardening and can drive off volatile aromatics prematurely, producing a flat, smoky flavor profile.
Weather-independent, faster throughput.
High capital cost. Temperature abuse common. Beans dried mechanically above 50°C frequently score lower in sensory evaluation than sun-dried equivalents.
Drying is not chemically inert. Acetic acid, the most volatile of the major organic acids, continues to evaporate throughout the drying period: a well-managed sun dry removes 30 to 60% of the acetic acid present at the end of fermentation. This is why drying duration and conditions affect the final acidity of the bean. Enzymatic browning (polyphenol oxidation) continues at a slower rate. Some ester formation and hydrolysis continues while moisture is present. As moisture drops below roughly 10%, enzymatic activity halts. Below that threshold, the bean is chemically stable.
Beans must be raked every 1 to 2 hours during peak drying periods. Raking prevents the outer layer from bonding into a crust (case hardening), equalizes moisture across the mass, and prevents the surface from becoming so dry that it inhibits evaporation from the interior. On raised beds, this is done by hand with a wide rake. Insufficiently raked beans dry unevenly: the outside reaches target moisture while the interior remains above 10%, creating a bean that tests correctly on a surface moisture reading but is actually too wet internally.
Smoke contamination during drying is a known defect in many commodity lots, particularly those dried over wood fires in enclosed spaces. Phenolic compounds from smoke adsorb onto the bean surface and into the fat, producing a persistent smoky, ham-like off-flavor that survives roasting and grinding. It cannot be corrected downstream. When evaluating a new lot of beans, smell the raw bean: a faint smoke or plastic note in unroasted cacao is a reliable early indicator of smoke contamination during drying.
What this means as a maker
You cannot undo what happened in the field. The fermentation and drying that produced your beans determined the flavor ceiling of everything you will make from them. Your roast, grind, and conche decisions operate within that ceiling; they cannot raise it. This is why sourcing transparency matters: knowing the fermentation method, duration, and cut test result is not a curiosity. It is process data that tells you what you have to work with.
The beans were under-fermented. Polyphenols were not adequately transformed. Conching reduces acetic acid but cannot reduce polyphenol astringency. The fix is in the sourcing, not the process.
The drying was probably too aggressive (high temperature mechanical drying) or the fermentation produced a limited ester and aldehyde precursor pool. The volatile aromatics were either never built or were driven off before you got the beans.
Harvest season, pod ripeness, fermentation duration, ambient temperature, and the microbial population in the fermentation environment all vary between lots. Two lots labeled with the same origin name can have fundamentally different fermentation histories.
Citric acid content in the pulp (set by terroir and variety) determines the baseline. Fermentation duration and drying management determine how much acetic acid remains. Origins like Madagascar are both higher in citric acid and often fermented shorter to preserve fruit esters, which together produce higher perceived acidity in the finished chocolate.
Log your bean source, fermentation notes (if available from your supplier), and how the finished chocolate tastes. Across enough batches, patterns emerge between processing transparency and cup quality.
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