When to cut perilla, how long to dry before threshing, the 10% moisture target, and why cold storage slows rancidity, based on Korean RDA and National Institute of Crop Science research.
The last ten days decide a perilla season. Wait a little too long for the pods to ripen and the seed pours onto the ground the moment you cut. Thresh well but bag it too damp, and a few months later the seed smells rancid.
With perilla, what you keep matters more than the market price. The same field can produce very different amounts of saleable seed depending on when it is cut, how it is dried and where it is stored.
Bottom line: cut when the top flower cluster is 60–80% brown, stand the plants up to dry for 6–9 days, then thresh. Dry the seed to about 10% moisture, and move anything kept past February into cold storage.
1. When to harvest perilla
Korea’s Rural Development Administration (RDA) puts perilla harvest at about 30 days after flowering: 32 days for early and mid-season types, 29 days for late types. Flowering usually runs from early to about September 20, so harvest centers on early October.
Visual signs:
- Stems and pods turn yellow.
- Seeds begin to change from white to brown.
- Pods on the top flower cluster turn brown.
Research by the National Institute of Crop Science (NICS) found the best timing was cutting when the top flower cluster was 60–80% brown. Cutting after full maturity caused an average shattering loss of 31.3%, close to a third of the crop left in the field.
2. Cut on cloudy days or in the morning and evening
Cut on cloudy days, or early morning and evening on clear days, when pods hold some moisture and open less. Sun-dried pods split at the touch of a sickle.
Stand cut plants upright, leaning against each other, in a well-ventilated spot. Plants laid flat dry poorly underneath and mold if rained on. Keep a tarp ready.
3. How long to dry before threshing
NICS recommends threshing 6–9 days after cutting. Too early and seeds cling to damp pods; too late and they drop while the plants stand.
| Scale | Method | Loss-reduction tip |
|---|---|---|
| Garden or small farm | Beat bundles with a stick or flail on a ground sheet | Lay a large tarp or threshing net first |
| Medium | Small thresher | Keep a sheet under bundles while moving them |
| Large | Mechanical cutting and threshing | Machines cut labor and shattering loss |
Most hand-threshing loss happens while moving bundles, so drag them on a sheet to the threshing spot.
4. Cleaning with wind and sieves
After threshing, seed is mixed with husks, stems, empty seeds and soil. RDA advises winnowing with wind: sieve out large debris, let the seed fall in a breeze or in front of a fan to blow off light chaff, then use a fine sieve for soil.
Cleaning affects price. Korea’s grading rules have no separate perilla category, but sesame allows at most 2.0% foreign matter for grade 1 and 3.0% for grade 2. Buyers judge perilla similarly.
5. Why dry to 10% moisture
Jeonbuk Agricultural Research and Extension Services advises drying perilla to about 10% moisture before storage. Sesame’s grading standard also caps moisture at 10.0%.
Damp seed heats in the bag and develops mold and off-odors. Sun-dry in thin layers and turn often. If using a dryer, avoid high heat and follow the manual’s seed setting for seed you intend to plant.
6. Why perilla goes rancid quickly
Perilla seed is about 45% oil, and about 60% of that oil is alpha-linolenic acid (omega-3). Over 90% is unsaturated fat, which oxidizes easily with air and heat.
In RDA trials over one year of storage, the acid value rose 97% at room temperature and 57% in cold storage. Because acid value starts rising four months after harvest, RDA recommends cold storage for seed held past February.
| Holding period | Storage | Reason |
|---|---|---|
| Sold within 3–4 months | Cool, shaded, ventilated room | Little rise in acid value |
| Held past February | Cold storage | Acid value rises after 4 months |
| Pressed for oil | Keep as seed until pressing | Oil oxidizes faster than whole seed |
For crop-by-crop storage conditions, see the cold storage temperature chart. For 2026 prices, see 2026 perilla seed prices.
FAQ
When should perilla be cut? About 30 days after flowering, when the top flower cluster is 60–80% brown. Cutting after full maturity raised shattering loss to an average 31.3%.
How many days after cutting should perilla be threshed? NICS found 6–9 days after cutting works best, adjusted for weather.
What moisture should stored perilla seed have? About 10%.
Why does stored perilla smell rancid? Its oil is mostly unsaturated fat that oxidizes easily. Cold storage cut the one-year rise in acid value from 97% to 57%.
Conclusion
Do not wait for perilla to fully ripen. Cut at 60–80% browning, dry upright for 6–9 days, thresh on a sheet, clean with wind and sieves, and dry to about 10% moisture. Then separate seed to sell soon from seed to hold, and keep the latter cold.
References
- RDA Nongsaro, perilla farm work schedule.
- National Institute of Crop Science, optimal perilla harvest timing and shattering loss, August 13, 2019.
- RDA, perilla cultivation techniques; Nongsaro farm-use technology on post-harvest perilla storage.
- Korea Agriculture News, Jeonbuk Agricultural Research and Extension Services guidance, 2013.
- Korea.kr policy briefing on perilla oil composition, May 23, 2012.
- National Agricultural Products Quality Management Service, grading standards (sesame).