Pongamia (Honge) Seed Quality for Biodiesel Feedstock
Pongamia pinnata — called honge in Kannada, karanja in Hindi and Sanskrit, pongam in Tamil, and Indian Beech in older trade literature — yields a non-edible oil that is one of the most established biodiesel feedstocks in India. Whole seeds typically contain 25–30% oil by dry weight; decorticated kernels run 30–40%. Free fatty acid (FFA) levels are naturally high at 4–18% depending on seed maturity, region, and storage conditions — buyers refine or pre-treat for this. Moisture must be at or below 10% before storage; above 12% and you are building a fungal problem that will push FFA higher still. At KVM & Co., we source and trade honge from the APMC Yard at Bandipalya, Mysuru, and the quality notes in this piece come directly from what we see on the yard floor.
What the tree is, and why it matters for trade
Pongamia pinnata (syn. Millettia pinnata) is a fast-growing leguminous tree common across South Asia. In Karnataka it lines roads, farm boundaries, and irrigation channels. The tree fixes nitrogen, tolerates drought, and bears fruit within four to five years of planting. That abundance is both an opportunity and a complication: honge is rarely a cultivated crop. Most lots come from smallholder collection, which means quality varies more than it does with field crops like groundnut or sesame.
Oil content: what the numbers mean in practice
ICAR and TERI research places honge kernel oil content at 30–40% dry weight; whole seeds including shell run 25–30%. The gap matters for pricing — you pay for shell weight too.
| Form | Typical oil content (dry weight basis) |
|---|---|
| Whole seed (with pod shell) | 25–30% |
| Decorticated kernel | 30–40% |
These are ranges, not guarantees. Oil content varies by region, variety, and rainfall in the harvest year. A dry Deccan season produces seeds with less fill; North Karnataka lots test at the lower end compared to wetter Malnad or coastal Karnataka material.
Free Fatty Acid (FFA) — the primary quality variable for biodiesel processors
FFA — free fatty acid, expressed as a percentage on an oleic acid equivalent basis — is a degradation marker. In a fresh, well-dried, properly stored seed, the cell walls keep triglycerides intact. As seeds age, get wet, or are damaged during threshing and transport, lipase enzymes cleave fatty acids from the glycerol backbone. Those freed fatty acids cannot be converted to biodiesel by the standard base-catalysed transesterification process without significant yield loss. They must either be esterified in a pre-treatment step (acid esterification) or removed by neutralisation, both of which add cost and chemical inputs.
Pongamia oil starts with higher FFA than most edible oils even under ideal conditions. Budget for pre-treatment. The question is how much pre-treatment — and that depends on seed quality at intake.
Typical FFA ranges for honge by lot quality are below. These numbers align with what we observe at the Bandipalya yard and with published NMBA and Indian Biodiesel Association procurement guidelines.
| Lot quality | FFA (% oleic acid equivalent) |
|---|---|
| Premium — freshly harvested, well dried, minimal damage | 4–8% |
| Standard trade — mixed maturity, adequate drying | 8–14% |
| Distressed — stored wet, old stock, high foreign matter | 14–18% and above |
Single-stage base-catalysed transesterification needs FFA below 8% to maintain yield. A two-stage acid-then-base process can handle up to 14%, though caustic soda and washing costs climb. Above 18% FFA, the refining economics rarely justify using the lot as biodiesel feedstock.
Moisture: the gating parameter for safe storage
Moisture content controls whether a seed lot is safe to store and what happens to FFA over time. The target for any honge lot entering long-term storage is 8–10% moisture (wet weight basis). At this level, microbial and enzymatic activity is slow enough that the lot holds for four to six months without major quality degradation.
Properly dried honge feels dry and slightly rough on the surface; it does not clump when a handful is compressed. Any clumping or softness is a warning sign. For commercial lots, require moisture meter readings at intake and specify the acceptable range in your purchase order.
Seed maturity: recognising good and bad at the collection point
Honge pods are harvested January through March in most of Karnataka. At maturity the pod turns dull straw-yellow or brown; the seed inside is plump and firm to the thumbnail.
- Immature seeds — shrunken, pale, light for size. Below-average oil content; FFA can be elevated due to incomplete cell membrane integrity.
- Mature seeds — plump, uniformly dark brown, heavy. This is the target.
- Over-mature or ground-fallen seeds — darker, sometimes wrinkled. Elevated FFA and possible insect damage.
Test weight is a useful bulk check. Well-filled mature honge runs 560–590 g per litre at our yard. Lots below 520 g/litre carry a significant proportion of light or damaged seed.
Post-harvest drying: the step most collectors skip
Dry the seed promptly after threshing — this single step has the largest impact on FFA at intake.
- Thresh and shell within two to three days of collection; do not let pods sit in heaps.
- Spread no more than 5–7 cm deep on clean cement or tarpaulin in direct sunlight.
- Turn twice daily — mid-morning and mid-afternoon — for four to seven days.
- Do not bag until a moisture meter reads at or below 10% on multiple sub-samples.
Skipping this step is the most common cause of FFA elevation in lots arriving at Bandipalya. The Karnataka honge season is relatively dry; poor drying is a time-pressure problem, not a weather problem.
South Indian vs. North Indian Pongamia: why region matters
Karnataka, Tamil Nadu, and Andhra Pradesh have a longer tradition of honge use and better post-harvest drying infrastructure. South Indian lots typically sit at the higher end of the oil-content range. North Indian Pongamia — from Uttar Pradesh, Rajasthan, and Gujarat — grows in more arid conditions; seeds tend toward the lower end of the 25–30% whole-seed oil range and our contacts report higher average FFA in fresh lots owing to longer transport distances to oil-extraction facilities. Run an oil content and FFA assay on North Indian lots rather than assuming South Indian quality parameters.
Foreign matter: what to specify and why
Foreign matter includes pod shell fragments, soil, stones, weed seeds, and damaged or mouldy seeds. For biodiesel use, up to 2% is typically acceptable. For bio-pesticide or soap-making, buyers often specify below 1%. At Bandipalya, unspecified lots arrive at 2–4% FM; a single pass through a mechanical aspirator brings most below 1.5%. Specify "cleaned and graded, FM below 2% on delivery" in your purchase order.
Bio-pesticide buyers: a different quality bar
Karanjin — the bitter tetranortriterpenoid that gives honge oil its insecticidal and antifeedant properties — is what bio-pesticide manufacturers and Ayurvedic ingredient buyers care about, not FFA. Karanjin content (typically 1.5–3% of oil weight) is not routinely reported in commodity trade; it requires HPLC analysis. Specify your karanjin floor in the purchase order, request a CoA from a NABL-accredited laboratory, and avoid mould-damaged lots — fungal activity degrades karanjin alongside FFA.
Purchase order checklist for honge procurement
Based on what matters at intake, a well-drafted purchase order for Pongamia seeds should specify all of the following:
- Moisture content
- Maximum 10% (wet weight basis) at delivery. Test by digital grain moisture meter on five sub-samples per lot.
- Free fatty acid
- State your maximum (e.g., "below 8% oleic acid equivalent") and the test method (AOCS Cd 3a-63 or equivalent).
- Oil content
- Minimum 27% for whole seed or 33% for decorticated kernel, by Soxhlet extraction on dry-weight basis (AOCS Am 5-04).
- Foreign matter
- Maximum 2% for biodiesel grade; maximum 1% for bio-pesticide or soap grade.
- Maturity admixture
- Immature and shrivelled seeds below 5% by count; visibly mouldy or insect-damaged seeds below 3% by count.
- Packing
- New jute or HDPE woven bags, 60 kg net. Specify minimum lot size.
- Certificate of Analysis
- Required per tranche above 5 tonnes, from a NABL-accredited laboratory.
A note on variation — and honest supply
Honge quality varies year to year. The tree is not a cultivated crop with agronomic inputs; most of the consistency comes from post-harvest handling — prompt drying, proper grading, clean bagging, covered storage. At KVM & Co., we have been handling oilseeds at Bandipalya since 1983, building on a family trade lineage in Mysuru since 1932. We will tell you when a lot does not meet your spec rather than ship it and manage the complaint later. For seasonal availability context, see our post on the seasonal calendar of Karnataka pulses and oilseeds.