Rural Industries Research & Development Corporation

The New Rural Industries
A handbook for Farmers and Investors

Peppermint Oil

Introduction

Peppermint oil is obtained from the leaves of the perennial herb, Mentha piperita L. a member of the Labiatae family. This family includes many well-known essential oil plants such as spearmint, basil, lavender, rosemary, sage, marjoram and thyme. The peppermint plant is a summer-growing perennial with upright square stems reaching a metre in height at maturity.

The oil is found on the undersides of the leaves, is extracted by steam distillation and is generally followed by rectification and fractionation before use. Its major end-uses are in toothpaste and mouthwashes, chewing gum and food flavourings.

World production is more than 4000 t/year, with the USA accounting for 90% of this and being, in addition, an importer and re-exporter.

The increase in world-wide demand is currently running at about 5% a year, predominantly as a result of Asian market expansion.

The environmental conditions under which peppermint is grown are critical to the quality of the oil produced and limit the areas suitable in Australia to Tasmania and Victoria. Long day lengths with warm to hot conditions and cool nights are required for the right balance of oil compounds to be produced during the growing phase. Most of Tasmania is therefore suitable and in Victoria the agricultural areas adjacent to the alps in the north-east of the State provide the right growing conditions.

Production has been under way in both these regions for many years and is currently expanding in the Victorian region. Production techniques are based to a considerable extent on U.S. practices and require a high level of capital input and expertise to produce a saleable product.

Markets and marketing issues

Prices in world markets are dictated by conformity with the characteristics of U.S.-produced oils, which differ from region to region. `Lower quality' oils typi-cally command a market price of about $A30/kg, whereas `higher quality' oils can fetch up to $A60/kg.

The buyers' primary concern is the quality and flavour of the product and the consistency from year to year.

This largely stems from the need for a consistent taste in the end-product formulated and delivered to customers.

The world-wide trade in peppermint oil is generally from growers to traders who may blend or rectify the oils from many growers or even regions to provide a consistent product to the flavour and fragrance houses which then supply pre-formulated product to the manufacturer.

Sales direct to flavour and fragrance houses and manufacturers do occur but require considerable long-term marketing commitment and well established production history.

The level of pesticide residues in the oil is now a key marketing issue. The top end of the market is very discerning and well equipped for residue detection.

Production requirements

Climatic constraint of areas suitable for production has already been mentioned. A major factor in this context is to minimise the production of less desirable compounds, in particular menthofuran.

Peppermint requires a relatively free-draining soil type with a pH of 6-6.5. Areas that lie wet in winter will not perform vigorously and plants may even die. Inundation during the growing season has even greater harmful effects.

The crop has high water demands in the summer. Crops are currently grown under managed flood, high pressure and low pressure irrigation systems. It is the ability to adequately irrigate which normally limits the growth or expansion of peppermint areas.

Pest and disease management are paramount and efficient broadacre spray equipment is a prerequisite.

Harvesting uses conventional forage harvesting technology but distillation of the oil requires specialist equipment and expertise and needs to be regionally based as large volumes of material must be processed.

Varieties

Mentha piperita L. is a sterile, perennial herb and therefore must be propagated vegetatively.

Two main selections are currently in commercial usage throughout the industry. Black Mitcham is the original cross. It is highly valued but susceptible to a soil-borne fungal disease, verticillium wilt.

Todd Mitcham is a more wilt-tolerant selection which now forms the bulk of the world's production.

Both selections are present in Australia where, to date, verticillium wilt has not been detected.

Agronomy

Using stolons from a nursery site of 1 ha, a cropping area of
7-10 ha can usually be achieved the following year.

As peppermint is a perennial crop, pre-planting weed control is imperative for the long-term viability of the crop. A well-planned fallow and weed eradication program before planting is therefore strongly recommended.

Specialised lifting equipment is used in Victoria and Tasmania to lift plants and remove soil. In Victoria, a specially designed planter is used to place stolon fragments evenly in rows. These rows rapidly close over and form a dense canopy in summer. In Tasmania lifted stolons are spread using modified muck spreaders followed by a light discing. Both planting processes work well.

Strong healthy planting material is essential for correct density of established crop.

Fertiliser rates are generally high, as development of the maximum number of leaves and their retention through to harvest is the target. Frequent nitrogen applications are required through the growing season and careful maintenance of soil fertility is needed to ensure the crop remains productive. A commercial crop correctly maintained will yield well for at least 5 years.

Because this plant is very succulent, proper timing of all operations is critical for the retention and maximisation of oil glands in the leaves. Oil yield will decrease rapidly if the plant is subjected to either physiological or pathological stress.

Pest, disease and weed control

The most significant disease problem encountered with peppermint is a rust fungus which, if left unchecked, will totally defoliate the plants.

The current method of control is to use the fungicide `Tilt' at strategic times in the life cycle of the rust fungus. The other important factors for control are efficient spray application, removal of any areas that are hard to spray and removal of rogue plants.

Pest problems encountered in Australia include cut worms, twospotted mite, brown vegetable weevil and wingless grasshopper,

Weed control programs must be strictly maintained to reduce plant competition but more importantly to eliminate oil contamination. There are herbicides registered for use in peppermint crops.

Harvesting, transport and distillation

The timing of harvest is critical to the quality of the oil. In Tasmania and Victoria an extensive pre-harvest sampling program is employed to schedule harvesting of all peppermint crops. This sampling examines changes in oil composition from early January onwards.

Peppermint crops are mown using conventional hay mowers or windrowers. It is very important not to bruise any of the leaves at any time during harvest as this will result in oil losses.

Once the cut herb is wilted it is chopped directly into a distillation vessel, usually referred to as a tub, using a forage harvester. The correct moisture content of the herb is essential for complete and economic oil extraction.

The tubs are then transported to the distillation facility where either wet or superheated steam is passed through the herb and the resulting steam and oil vapour are condensed and separated.

Condensing and separation equipment should be manufactured from stainless steel and general processing hygiene followed to ensure no contaminants are present.

In general, the most-economic units distil five or more tonnes of herb at a time. The time for oil extraction varies depending on the type of steam source, the herb weight and the moisture content.

Most distillation units are diesel-fired but wood-fired units are used in Tasmania with success.

Once the oil is separated, the product is relatively stable for many months provided it is stored out of direct sunlight and away from heat. Epoxy-lined and galvanised drums are the commonly used storage and transportation units.

Economics

The costs of establishing a peppermint crop are considerable because propagation is vegetative, as described above. In general, a minimum area of 5 ha is needed within an existing essential oil distillation region of radius 30 km. For a distillation region to be viable a minimum of approximately 80 ha is necessary.

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

The following table (not available in this html version) is a gross margin analysis for a typical Tasmanian or Victorian peppermint crop of 5 ha or greater.

It should be noted that the gross margin is highly sensitive to yield and price changes. Production costs tend not to vary greatly.

Key contacts

Key references

Guenther (1948) The Essential Oils - Krieger

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

Aretander (1960) Perfume and Flavor Materials of Natural Origin - Aretander

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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