Rural Industries Research & Development Corporation

The New Rural Industries
A handbook for Farmers and Investors

Fennel Oil

Introduction

Fennel (Foeniculum vulgare) is a member of the Apiacae family, formerly known as the Umbelliferae. Other members of this family include parsley, coriander, dill, parsnips and carrots.

The essential oil is produced in canal-like structures formed by glandular cells throughout the plant but with the most prominent canals present in the seed coat.

The production of fennel for its essential oil in Australia has been limited to Tasmania where production began in 1982 and peaked some 10 years later.

The fennel project in Tasmania was developed for the commercially valuable compound, anethole. This compound is used in many anise flavoured beverages popular in European countries and has been traditionally sourced from the fruits of star anise, a member of the magnolia family. The same compound is present in fennel oil, enabling development of a more broadacre approach to its production.

Unfortunately, Australia has not been able to remain competitive with Chinese and Vietnamese star anise production and the remaining fennel production in Tasmania is for the fennel oil in its own right.

Fennel is a deep-rooted perennial which produces 95% of its oil within the coating of its seeds, which are held on one umbel. This has enabled simple grain harvesting and handling systems to be modified and used for harvest. Depending on what sort of oil is required and the transportation arrangements available, the crop can be direct headed or forage harvested and then steam distilled.

Markets and marketing issues

World production of anethole is about 1000 t/year, with China and Vietnam being the dominant producers from star anise. Recent improvements in the continuity and quality of supply from China, as well as price reductions, have seriously affected Australian production of fennel oil for anethole. Production is now less than 1 t compared with a high of 40 t in 1992.

The production of anethole from fennel oil requires specialised rectification equipment to produce the 99% pure product that the market requires.

Present world-wide trends are towards decreased consumption of anethole-based beverages.

The present market for fennel oil is the flavour industry where the balance of anethole with other important flavour components is vital.

While anethole sales in the past have been direct with end-users, fennel oil sales are generally handled through the normal essential oil marketing chain of grower to trader to flavour and fragrance house to end user.

Production requirements

Fennel has been grown successfully on a variety of soil types, from sandy loams to black cracking clays.

Irrigation is essential, particularly during flowering and seed development. Flood irrigation is not recommended as this is reported to cause root disease problems.

Once established, the amount of vegetative material produced by the fennel plant is considerable and plants may grow to over 2 m. It is crucial to maintain cultural practices during the early development of the crop otherwise accessibility becomes difficult and, if applications of fertiliser or pesticides are needed, they must be done so from the air.

Fennel has the added bonus of improving soil structure due to the large amounts of vegetative material that it returns to the soil and its aggressive deep rooting habit. The crop can also be grazed by stock over winter.

Fennel can be harvested with forage harvesting machinery similar to that used for peppermint. However, the crop does not have to be wilted and is cut at a height which removes mainly seed heads. Direct heading of the crop is also successful using regular combine harvesters.

The fennel oil is extracted by steam distillation, a techniques requiring specialised equipment and expertise. Direct heading of seed significantly reduces the volume of herb to be processed. This extends the radius from a distillation facility that the crop can be grown economically.

Varieties

The classification of fennel has in the past been disputed by many researchers, but the general agreement today is that there is only one species, Foeniculum vulgare M., with two sub-species, piperitum and capillaceum.

Recurrent selection programs have been undertaken in India and France to increase seed yield, oil content, oil quality, pest and disease resistance.

The varieties commercially grown in Tasmania have been a result of a joint program by the Pernod-Ricard company and the University of Tasmania. The program was initiated by Pernod-Ricard in the quest for higher yields of anethole per hectare. A large range of selections is available, depending on the oil characteristics required. In general an oil low in the compound fenchone is required for the flavour market as this is an intensely bitter agent.

Agronomy

Fennel crops can be established easily by direct seeding in spring. with a target density of
10 plants/square metre. Because the seed is small, best results have been obtained using some form of precision seeder. Good seed to soil contact is essential for uniform germination. In general the gemination and initial development of the seedling is slow and no herbicides can be used until the plant has developed at least 3 pairs of true leaves.

Fennel is a typical long-day plant and will remain vegetative until the day length exceeds 13.5 hours, after which the plant initiates flowers and bolts very rapidly.

Fennel can reach maximum yield in the first year and, with careful maintenance, can maintain that yield for 6-7 years.

Fertiliser requirements are relatively high and require annual soil analysis to monitor changes. To date, no major trace-element deficiencies have developed over a 5-year life span. Nitrogen applications are critical, especially during flowering.

After two years the crop benefits from deep ripping. This alleviates soil compaction, promotes new adventitious root growth, and lowers shoot density. If the shoot density is not checked in later years yield can be decreased.

Agronomic practices are aimed at promoting maximum seed yield and maximum seed size.

Harvest date prediction is not as critical as peppermint as the oil composition is largely determined by the variety. The more important factor is the minimisation of seed loss. The umbels on fennel mature at different rates and it is important not to leave the crop too late as seed lost from the earliest maturing umbels will shatter. Forage-harvested fennel crops can be harvested earlier than direct heading which requires a lower moisture content for successful seed removal and oil extraction.

Pests and diseases

The major disease problem in fennel is a Cercosporidium fungus. This can be managed with early preventative fungicide applications to reduce the level of inoculum. High humidity during flowering will promote Cercosporidium development, such that heavy leaf loss and damage to developing flowers and seed will be sustained.

Late infections can be controlled by fungicide application, but usually the only option is using the less desirable aerial techniques.

The major yield-reducing pests of fennel have been thrips, potato myrid and aphids. Particular care has to be taken with insect pest management during flowering as bee activity is vital for pollination and subsequent seed set.

Harvest, transport and distillation

As mentioned previously, fennel can be either forage harvested or direct headed. The stage of maturity at which each harvest type can commence varies, allowing for considerable flexibility in the harvest period and better utilisation of distillation equipment.

The volumes of crop to be transported to the distillation unit vary greatly between the two methods: heading allows for crops further away from a distillation unit to be economically processed. Conventional grain handling methods can be used for the handling of headed fennel seed, but as the moisture content is much higher than in grain, the product has to be extracted promptly and some handling difficulties may occur. It is important for ease of heading and complete extraction of oil by steam distillation that the seed has the correct moisture content at the time of harvest.

The plant and equipment used for distillation of peppermint can also be used for extraction of fennel oil. If distillation facilities are used for more than one product, it is imperative that tubs and condensers and separators be cleaned between uses.

Once the oil is extracted and separated, the product is relatively stable for many months provided it is stored out of direct sunlight and away from heat. Poly-lined drums are not suitable for fennel: only galvanised or lacquered drums may be used for its storage and transport.

Economics

Fennel crops are established by direct seeding. It is important to use some form of precision seeder to establish the correct plant density. To date seed costs have been relatively low.

The major advantage of fennel is its robust perennial nature. Proper maintenance has allowed crops in Tasmania to yield nine commercial harvests.

As with most essential oil crops the major costs are those for the harvest, transport and distillation. On-farm costs are limited to fertilisers, pest and disease control, and irrigation, and for slashing the stubble after harvest and some form of ripping or interrow cultivation in subsequent years to maintain vigour.

Contractors can be used for direct heading of fennel, but forage harvesters must be modified if the crop is to be collected in this fashion.

Capital outlay for distillation equipment such as boilers, condensers, separators, and tubs is considerable. In general, even with second-hand equipment, set-up cost have been in the order of $150,000-250,000 for a regional facility.

Mobile distillation units have been trialed in Australia but the strict regulations covering boilers have led to both economic and strategic failure.

The following table (not available in this html version) is a typical gross margin analysis for fennel oil production.

Key contacts

Key references

Guenther (1948) The Essential Oils - Krieger

Hay and Waterman (1993) Volatile Oil Crops - Longman Scientific and Technical

R&D Plan for the Essential Oils and Plant Extracts Program 1996-2001, RIRDC October 1996

Proceedings of the Essential Oils Planning Workshop, RIRDC, June 1996

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