Desert Lime

24.05.17

Desert lime (Citrus glauca) is one of several true citrus species native to Australia. Also known as bush lime, wild lime or native cumquat, it is found in south west Queensland, western New South Wales and a small area of the Flinders Ranges of South Australia. Desert lime can vary in size from a compact multi-stemmed tree, two to four metres high, to a slender spiny tree up to 12m. Trees often appear in groups formed by suckering, particularly where heavy grazing has occurred.

Overview

Natural adaptations to growing conditions include sharp thorns found on younger, smaller plants as a natural defence from grazing animals, and the ability to withstand drought by shedding leaves. These upward facing leaves are slender and blue-grey in colour with white flowers appearing in spring.

Citrus glauca is the quickest citrus species in the world to set fruit after flowering. Ripening in summer, the small rounded fruit are light yellow-green when mature, with a thin porous rind and piquant lime flavour.

Desert lime is sold in both domestic and international markets, and is favoured by the food service industry. It has a wide variety of culinary uses and is also used in the manufacture of cosmetics and pharmaceuticals.

Traditionally collected in the wild by Indigenous Australians, the desert lime has high levels of vitamin C, folates and antioxidants. Early settlers used the fruit in traditional citrus recipes like jams, tarts, jellies, preserves and cordials.

Growers of Desert Limes usually grow other species of native foods and other citrus which helps to spread income risk. Australian native foods growers are represented by Australian Native Food & Botanicals (ANFAB).

Facts and figures

  • Desert lime is one of several true citrus species native to Australia
  • Endemic to south west Queensland, western New South Wales and a small area of South Australia, desert limes are cultivated commercially across Australia
  • The plant can withstand extreme temperature variation, from -12°C to 45°C
  • Desert lime trees are tolerant of heat, frost, drought and salinity

Production status

Established in the early 1990s, the desert lime industry is dominated by a single large plantation (32 hectares) in south west Queensland, and with additional supply by wild harvest (constrained by severe and widespread drought since the mid-2000s) and production from smaller blocks in the eastern regions of southern Queensland (which are orchards established using plants from the large plantation).

In order for the desert lime industry to move from niche to commercial production, particularly as development of products such as desert lime puree broadens its market appeal in the food service industry, larger scale plantations are needed to remove the reliance on wild harvest.

Key production regions for desert lime are based throughout Australia. In Queensland, desert limes are produced at Townsville and from Winton through to Roma. Other production regions include western New South Wales, Victoria and Port Augusta in South Australia, and more recently, in south west Western Australia.

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Map of current and potential growing regions

Uses

The desert lime’s distinctive piquant lime flavour and refreshing taste means that it can be used in any context that a standard lime or citrus fruit can be used.

The mature ripe fruit or pulp are sold either fresh, frozen or pureed, and used in a wide variety of food and beverage products. Desert lime puree, made from the whole fruit without additives or preservatives, has been a recent innovation convenient for use in food service and manufacturing. It retains the distinctive intense flavour of the desert lime fruit and when packaged has an 18-month shelf life at ambient temperatures, thereby reducing storage and freight costs. Potential use is in beverages, condiments, confectionery, ice cream and sorbets.

Desert lime is also available to the market in juice or “spice” form, where the whole fruit is dried and ground into a seasoning powder, which is used in applications like coating nuts including macadamias. The fruit’s thin rind is virtually tasteless and it is often seedless, making it an extremely versatile and excellent processing and culinary fruit.

The desert lime is used in many other value-added products, including dressings and marinades, chutneys, jams, pickles and preserves, brined peel and candied products. Other uses include flavoured butters, cordials, syrups and liqueurs.

Desert lime can be incorporated into a variety of sweet and savoury dishes, including frozen desserts, baked goods and seafood and poultry dishes. Segments, slices and fruit salads are canned, and the essential oil is used in flavourings and chemicals. There is an opportunity for desert lime to deliver new products in the cosmetic and pharmaceutical industries, including anti-ageing and sunscreen products, and it has recently been incorporated into cosmetic products such as hand lotion.

Desert lime shows the highest source of folate amongst the key commercial native food crops, and is a very rich source of calcium. High in vitamins C and E and also lutein (which is good for eye health and wellbeing). It also has a high potassium: sodium ratio, which may help to reduce blood pressure.

A number of research projects have been conducted to understand and investigate the properties of desert lime, and other native foods, including the Health Benefits of Australian Native Foods, Potential Physiological Activities of Selected Australian Herbs and Fruits and defining the flavours of native foods.

Research reported in Functional Properties of Australian Bushfoods indicated that native lime extracts show strong activity against common food spoilage bacteria which cause food poisoning outbreaks.

Production Requirements

Growing regions

Desert lime is endemic to the semi-arid regions of eastern Australia, extending from Rockhampton to Winton in Queensland, south to Dubbo in central New South Wales and west to Quorn in the Flinders Ranges of South Australia. The plant grows naturally in inland woodlands and brigalow scrubs, in a range of soil types and is tolerant of heat, frost, drought and salinity.

Commercial production is currently based around Townsville, from Winton through to Roma in Queensland, in western New South Wales, Victoria and at Port Augusta in South Australia.

Soil type

Desert lime can grow in a wide range of soil types from acid to neutral and alkaline but may benefit from the application of trace elements in alkaline soils. However, trees do best when planted in fertile, well-drained soil that is kept moist, as they will shed fruit after flowering if soil moisture is lacking. Desert lime are reasonably tolerant of salinity but this should be trialled before plantations are established.

Climate

Desert lime trees evolved across the challenging climatic zone of Australia’s inland. Trees can withstand extremes in temperature, ranging from -12°C to 45°C, and are tolerant of heat, frost and drought.

Varieties

Australia has several species of native lime, offering unique flavour and texture qualities. The native foods industry is very interested in these species but has found yields from wild harvested trees inconsistent and the fruit small.

The CSIRO has developed three high-yielding citrus varieties with larger than normal fruit, consistent yields and the unique flavour and texture of Australian native limes. The varieties have proved suitable for plantation production using standard horticultural practices and are now available for domestic gardeners.

‘Australian Outback’ (also known as ‘Australian Desert’) is a variety selected and developed from a collection of different native desert lime trees. It produces small green, juicy fruits which ripen at Christmas time. Its fruits can be used for preparing sauces.

A number of nurseries in Western Australia, Victoria, New South Wales and Queensland have contracts with CSIRO Plant Industry to propagate and distribute trees from native lime varieties.

Planting and crop management

Desert limes are normally slow growing, like most of the native Australian citrus species. In the wild, they can take 10 years to reach fruiting age, however when grown in cultivation they are usually grafted, which makes them faster maturing, more productive, fruit bearing within three years and less likely to sucker. Commercially suitable trees are grown by taking proven high-bearing wild trees and grafting to a citrange rootstock.

In a trial of six native food species outlined in the report Cultivation of Native Food Plants in South Eastern Australia, establishment and survival of the desert lime was excellent – close to 100% – and the plant remained vigorous despite low levels of fertiliser being applied. Wind was a factor in reducing vigour in some sites, especially if combined with cold conditions. The adaptability to different soils and climates probably can be attributed to the success of the grafted rootstock.

Recommended commercial plantings are at 5m spaces between trees and with 5m row width, resulting in 400 trees/ha. However 625 trees/ha (4m x 4m spaces) is also possible.

Agronomy for desert lime is similar to other citrus, with trees responding favourably to fertiliser and irrigation. The soil should be kept moist but not overwatered. Foliar fertiliser sprays after flowering are recommended to promote tree health and fruit set. Fish emulsion or seaweed solutions have proved useful. Trace element application may be necessary on alkaline soils.

Trees should be planted in full sun and avoid the root zone of large trees. It is best not to prune for the first five years and then only moderately, removing any suckers from below the graft line and keeping low hanging fruiting branches clear of the ground.

Weeds, pests, and diseases

Weed control is important when preparing the site for planting, as weeds will compete with new plants for water and nutrients. Ongoing maintenance of plant rows and inter-row areas, through chemical or physical removal of weeds, is required to optimise productivity.

If desert lime trees are kept healthy and stress free, there will be very few pest problems. They have so far proven to be highly resistant to the plant disease Phytophthora root rot, a form of ‘dieback’ that can affect many native plants, crops and horticultural plants. The desert lime is considered to be a minor host of fruit fly, and should be treated for insects such as scale.

Desert limes can be affected by citrus canker, however since the last outbreak in Emerald, Queensland, in 2005, Australia has been free of this bacterial disease. As with other diseases, prevention is best achieved by employing good sanitation and hygiene practices, establishing new plantings from reputable sources and being familiar with and able to recognise the diseases symptoms. The Queensland Government fact sheet on citrus canker provides more information.

Infrastructure Requirements

When not harvested in the wild, desert lime is generally grown in small-scale commercial bush-food orchards. Cultivation of desert lime requires standard equipment for orchard maintenance such as a tractor, mower or slasher, sprayer and pruning equipment.

An irrigation system with a reliable water supply is required to maximise production. Soil moisture monitoring equipment is also recommended. As the desert lime does not perform as well in windy conditions, particularly if combined with cold temperatures, some form of wind protection such as trees, mesh or screens, may be required.

Harvesting equipment for desert lime can include pole pickers and collection boxes or tubs, as they are mainly hand-harvested and then sorted to remove foreign matter. If using the ‘shake and collect’ method, nets will be required to catch the fallen fruit. Immediately after harvest, the limes should be promptly refrigerated or frozen, or alternatively cool storage should be maintained throughout the supply chain, depending on market destination and requirements.

Harvesting & Processing

Desert limes flower in August, with fruit ripening by November–December. The flower-to-fruiting time is around 10–12 weeks, which is the shortest of any citrus species. Ripeness is indicated by a colour change from green to yellow, although the fruit can be picked when still green. At this stage the fruits are approximately 2cm in diameter, weighing 1–3g.

Desert limes are usually handpicked, however fruit intended for manufacturing (which is most of the industry output) has the potential to be mechanically harvested. Premium fruit can be harvested using the same mechanical aids as olive production.

The harvest is graded into three sizes before sale: small for manufacturing — usually processed into a puree; medium, which is preferred by the food service industry where fruit is used whole; and premium large, where fruit is sold in whole frozen form or bottled and preserved in syrup.

Desert lime should be refrigerated almost immediately after picking, where it can be stored for 3–4 days if being sold fresh. Otherwise freezing is recommended, as the fruit can be stored frozen for long periods and retains its form and flavour very well when thawed. Desert lime can also be stored as a dry powder.

Markets & Marketing

Until recently, most native citrus came from wild harvest, which constrained industry expansion as annual yields were highly variable. A commercial industry based on desert lime was established in the early 1990s, reducing the need to harvest limes from the wild, improving the reliability of supply and minimising any detrimental impact on wild populations.

However, new contracts are expected to see the industry double annual production to meet the increased demand. In 2012, the native food industry stocktake reported that industry participants believe direct retail sales will continue to be important but the industry’s future appears to lie in the provision of reasonably priced puree for use in gourmet manufactured products.

A lot of fruit is sold as puree to food manufacturers but most growers value-add themselves.

Risks & Regulations

Risks/challenges

There are several challenges common to all native food producers and their industry more broadly, such as annual variation in production volume and maintaining a consistent supply of product to customers, and concurrent oversupply of niche markets and undersupply of potential large-scale markets.

Supply of desert lime is variable, with wild harvest dependent on seasonal conditions. Cultivated crops are also subject to the vagaries of water availability, with severe droughts limiting irrigation water supply. Production variability is forecast to decrease as the industry moves away from wild harvest to cultivated limes.

In 2012, the desert lime market was oversupplied for the small boutique markets. As reported by the native food industry stocktake, agreements to supply a major manufacturer are expected to change market dynamics, and the market will move from oversupply to undersupply until new and planned plantations come into production.

Regulatory considerations

The standard regulatory considerations that apply to all Australian farms, including laws applying to chemical use and management, occupational health and safety and transport (including machinery movements and the loading/unloading of harvested product), also apply to desert lime production.

Desert lime is classified by Food Standards Australia New Zealand (FSANZ) as a traditional food of Australia and it is included in the FSANZ nutrient tables. Desert lime is listed under the Codex Alimentarius system, which is required to import food products into Europe.

Certification by organisations such as Freshcare and HACCP may be required to sell product to supermarkets, major retailers and food service industries. Prospective growers should speak with potential customers to understand fully any product certification requirements. When processing any raw product and value-adding, food standards regulations, as administered by FSANZ and set out in Chapter 3 of its Food Standards Code need to be considered.

Publications

Publications/Information

Focus on Desert Lime RIRDC Fact Sheet (2014)

Desert lime published on the website of Australian Native Food & Botanicals

Australian Native Food Industry Stocktake RIRDC report (August 2012)

Nutritional Data for Australian Native Foods RIRDC report (Oct 2012)

Defining the Unique Flavours of Australian Native Foods RIRDC report (May 2010)

Health Benefits of Australian Native Foods RIRDC report (2009)

Functional Properties of Australian Bushfoods RIRDC (2007)

Cultivation of Native Food Plants in South Eastern Australia RIRDC report (Feb 2005)

The New Crop Industries Handbook RIRDC report (Sep 2004)

Image Gallery

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Harvested desert limes

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Desert lime fruit on the tree

Related Publications

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Focus on Desert Lime

10.08.12

Australian Native Food Industry Stocktake

26.10.12

Nutritional Data for Australian Native Foods: Supporting the Food Standards Australia and New Zealand Nutritional Panel Calculator

03.05.10

Defining the Unique Flavours of Australian Native Foods