Cherry growing in Australia is a rewarding but challenging endeavour, with the delicate nature of the fruit demanding meticulous care, especially after harvest. The window between picking and consumption is critical for maintaining quality, flavour, and market value. By implementing effective post-harvest strategies, growers can significantly extend the shelf life of their cherries, reduce spoilage, and ensure a premium product reaches consumers. This article provides practical, actionable tips for optimising your post-harvest processes.
Gentle Harvesting and Handling Techniques
The journey to a long shelf life begins even before the cherries leave the tree. Rough handling is one of the primary causes of post-harvest damage, leading to bruising, skin breaks, and accelerated decay.
Hand-Picking for Quality
Whenever possible, hand-picking is the preferred method for cherries destined for the fresh market. Train your picking crew thoroughly on proper techniques:
Handle by the Stem: Always pick cherries by their stems, avoiding direct contact with the fruit itself. This prevents bruising and preserves the delicate skin.
Gentle Placement: Place picked cherries gently into picking buckets or bins, rather than dropping them. Use shallow containers to prevent the weight of upper layers from crushing those below.
Avoid Overfilling: Do not overfill containers. This reduces pressure on the fruit and minimises damage during transport from the orchard.
Timely Harvest: Harvest cherries at their optimal ripeness. Over-ripe fruit is softer and more susceptible to damage, while under-ripe fruit may not develop full flavour.
Minimising Field Heat and Damage
Field heat is detrimental to cherry quality. The warmer the fruit, the faster its metabolic processes, leading to quicker deterioration.
Harvest During Cooler Hours: Schedule harvesting during the coolest parts of the day, typically early mornings or late afternoons, to minimise initial fruit temperature.
Shade Protection: Immediately after picking, move harvested cherries into shaded areas. Never leave bins exposed to direct sunlight.
Careful Transport: Use vehicles with good suspension for transporting fruit from the orchard to the packing shed to reduce vibrations and bruising. Drive carefully and avoid sudden stops or turns.
Rapid Cooling and Hydro-cooling Methods
Rapidly removing field heat is perhaps the single most important step in extending cherry shelf life. For an overview of essential orchard management, consider exploring resources like Cherrybox for industry best practices.
The Importance of Rapid Cooling
Every hour cherries remain warm after harvest significantly reduces their potential shelf life. Rapid cooling slows down respiration, moisture loss, and the growth of decay-causing microorganisms.
Hydro-cooling Explained
Hydro-cooling is the most effective and widely used method for cherries due to their small size and high surface area. It involves drenching or immersing fruit in chilled water (typically 0-1°C).
Mechanism: Cold water rapidly draws heat out of the fruit. The water also helps to clean the fruit and can be treated with sanitising agents.
Equipment: Hydro-coolers range from simple batch systems to continuous conveyorised units. Ensure your system can cool fruit to the target internal temperature (around 1-2°C) within 15-30 minutes.
Water Quality: Maintain excellent water quality. Regularly filter and sanitise the water (e.g., with chlorine or peracetic acid) to prevent the spread of pathogens. Monitor pH levels to ensure sanitiser efficacy.
Common Mistake: A common mistake is not cooling the fruit quickly enough or to a low enough temperature. Aim for a core temperature of 1-2°C as soon as possible after harvest.
Optimal Storage Temperature and Humidity
Once cooled, maintaining precise temperature and humidity is paramount for long-term storage.
Temperature Control
Near Freezing: Cherries store best at temperatures as close to 0°C as possible without freezing (typically -0.5°C to 0°C). Each degree above this ideal temperature significantly shortens shelf life.
Consistent Temperature: Avoid temperature fluctuations, which can lead to condensation (sweating) on the fruit, promoting fungal growth and decay.
Pre-cooling Storage Rooms: Ensure your cool rooms are pre-cooled to the target temperature before introducing fruit.
Humidity Management
High Humidity: Cherries are highly susceptible to water loss, which leads to shrivelling and loss of firmness. Maintain relative humidity levels between 90-95% in storage.
Humidifiers: Use industrial humidifiers in cool rooms if natural humidity is insufficient. Regularly monitor humidity levels with accurate sensors.
Packaging: Proper packaging (e.g., perforated plastic liners in bins) can also help create a micro-environment with higher humidity around the fruit.
Atmosphere Control and Modified Atmosphere Packaging
Controlling the atmospheric composition around cherries can further extend their shelf life by slowing respiration and ripening processes.
Controlled Atmosphere (CA) Storage
CA storage involves precisely managing the levels of oxygen (O2), carbon dioxide (CO2), and nitrogen within a sealed storage room.
Reduced O2: Lowering oxygen levels (e.g., to 3-5%) significantly slows down the fruit's respiration rate.
Elevated CO2: Slightly elevated carbon dioxide levels (e.g., 10-15%) can inhibit the growth of certain decay organisms and maintain firmness, but too much can cause fruit injury.
Benefits: CA storage can extend cherry shelf life by several weeks or even months beyond conventional cold storage, depending on the variety.
Expertise Required: CA storage requires specialised equipment and expertise to monitor and maintain gas levels precisely.
Modified Atmosphere Packaging (MAP)
MAP involves packaging cherries in films that create a modified atmosphere within the package itself.
Permeable Films: Specialised plastic films with specific gas transmission rates are used. These films allow some O2 to enter and CO2 to exit, creating an optimal internal atmosphere (lower O2, higher CO2) for the fruit.
Individual Packages/Liners: MAP can be applied to individual punnets or as liners within larger cartons or bins.
Reduced Decay: MAP helps to reduce moisture loss, slow respiration, and inhibit the growth of decay pathogens, particularly during transit and retail display.
Ventilation: Ensure packaging has appropriate micro-perforations. Insufficient ventilation can lead to anaerobic conditions and off-flavours.
Post-Harvest Treatments and Coatings
Certain treatments and edible coatings can provide an additional layer of protection against decay and moisture loss.
Fungicides and Sanitizers
Pre-cooling Dips: Applying approved fungicides or sanitising agents (e.g., chlorine, peracetic acid) as a dip or drench during the hydro-cooling process can significantly reduce the incidence of post-harvest rots like Botrytis (grey mould) and Monilinia (brown rot).
Strict Adherence: Always follow manufacturer's instructions for concentration, contact time, and safety precautions. Ensure chemicals are approved for use on cherries and meet local regulatory standards.
Resistance Management: Rotate fungicides to prevent the development of resistant strains of pathogens.
Edible Coatings
Moisture Barrier: Edible coatings (e.g., based on carnauba wax, shellac, or plant-based polymers) can create a semi-permeable barrier on the fruit's surface. This reduces water loss and can enhance the fruit's appearance.
Gas Exchange: Some coatings can also modify the internal atmosphere of the fruit, further slowing respiration.
Application: Coatings are typically applied as a spray or dip after hydro-cooling and before packing. Ensure even coverage for optimal results.
Consumer Acceptance: Choose coatings that are food-grade, tasteless, and do not negatively impact the fruit's natural appearance or texture.
Identifying and Preventing Common Post-Harvest Issues
Proactive identification and prevention are key to minimising losses.
Common Issues and Their Causes
Bruising and Pitting: Caused by rough handling, dropping, or excessive pressure during picking, packing, or transport. Prevention: Gentle handling, appropriate packaging, and careful logistics.
Shrivelling/Dehydration: Result of excessive moisture loss due to low humidity, high temperatures, or prolonged exposure to dry air. Prevention: Rapid cooling, high humidity storage, and protective packaging.
- **Grey Mould (Botrytis cinerea):** A common fungal disease that appears as a grey, fuzzy growth. Often starts from stem-end infections or wounds. Prevention: Gentle handling, rapid cooling, sanitation, and fungicide treatments.
- **Brown Rot (Monilinia fructicola):** Another significant fungal pathogen, causing soft, brown lesions. Prevention: Field sanitation, rapid cooling, and fungicide treatments.
Stem Browning: Can be caused by dehydration or physiological stress. Prevention: Maintain high humidity and cool temperatures.
Off-Flavours: Can result from anaerobic conditions (e.g., in poorly ventilated MAP), chilling injury, or exposure to ethylene. Prevention: Proper atmosphere control and avoiding ethylene sources.
Monitoring and Quality Control
Regular Inspections: Implement a robust quality control programme. Regularly inspect fruit at various stages: upon arrival at the packing shed, after hydro-cooling, and before packing.
Temperature Logging: Use data loggers to monitor temperatures throughout the cold chain – from orchard to cool room to transport. This helps identify potential warm spots or temperature abuse.
- Traceability: Maintain detailed records of each batch, including harvest date, orchard block, cooling time, and storage conditions. This allows for quick identification of issues and continuous improvement.
By diligently applying these practical tips, cherry growers can significantly enhance the post-harvest quality and extend the shelf life of their valuable crop, ensuring a superior product reaches the market and strengthens their brand reputation. For more insights into agricultural technology and best practices, visit Cherrybox and explore the resources available.