This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

Chestnuts were harvested over a short period of a few weeks, but were in demand by consumers over the cooler months of the year. At the time, external mould was major a problem, often limiting storage of high quality nuts to less than two months. A new technology had been developed for the Australian chestnut industry that enabled chestnuts to be stored for over nine months without significant external mould. Control of mould was based not on pesticides, but rather on using the natural respiration of the chestnuts to raise the carbon dioxide level around them to high levels (> 15 per cent) and reducing oxygen levels to below 5 per cent. This was achieved with technology developed in this project which combined special airtight packaging around the bins of chestnuts and an inexpensive oxygen/carbon dioxide controller that ran on 12V DC. This system was known as CALM (Controlled Oxygen Longlife Module) and one unit was capable of controlling the oxygen/carbon dioxide levels of up to 1.6 tonnes of chestnuts stored in four half tonne bins. The current CALM version was Version 7. Multiple CALM units could be used within a coolroom and the ability to remove a bin at time from a stack enabled maximum flexibility in marketing. This flexibility was not possible with a controlled atmosphere room.

The system integrates well with normal chestnut handling and cool storage and provided safe pesticide free chestnuts. Suggested modifications to postharvest handling at the time helped optimise chestnut quality, included correct harvesting, sanitizing, slight weight (water) loss of 1 to 3 per cent before storage using the CALM system at about -2°C. This system enabled growers to greatly improve the quality of their chestnuts, enabling good prices to be obtained throughout the cooler months of the year. Indeed with the CALM system and recommended handling quality chestnuts could be stored for over 9 months compared with the current 2-3 months. Further work was required to continue fine-tuning the system to integrate in the most practical and cost effective way in the Australian chestnut industry. This system had the potential to be expanded to benefit a considerable number of horticultural crops (ie other nuts and berry fruits) and it was recommended that research be done to enable this. CALM units developed for other crops besides chestnuts, were given different series names to signify this i.e. CALM Sv3 for the Strawberry version.

The chestnut production in Australia according to the most recent statistics at the time was worth $6.8 million, with almost of the nuts consumed domestically. The losses during storage without the advanced disease control achieved by CALM systems would have been at least 10 – 15 per cent, or $0.5 to 0.8 million dollars. The use of the CALM system (together with other suggested procedure changes) was expected to reduce these losses by at least 2/3rd, giving a total potential benefit to the Australian industry of $0.3 to 0.6 million dollars. The cost of a CALM system was about $1,000, with increased returns to growers from each CALM system already established as worth between $1,000 to $5,000 per annum.