Ripening

There may be periods in the season where the fruit you have in inventory is too firm to meet the specifications of your customers. In these circumstances it can be beneficial to conditioning your fruit in order to ensure it achieves such firmness requirements. This section of the site provides plenty of helpful tips and advice to help you ensure your conditioning programme is a success. 

It's best practice to be cautious when attempting to condition fruit. Depending on your position in the supply chain your target firmness ranges will vary. In the first instance Zespri strongly recommends that you follow your own company's ripening protocols where possible and refer to the information contained within this section simply as a guide. Before undertaking any of the conditioning activities mentioned below it is also recommended that you review the Assess section of this site, to better aquatint yourself with kiwifruit assessment process.

Ripening Principles

There are a set of key principles which need to be considered before you attempt to ripen your kiwifruit. it comes to ripening kiwifruit - if followed correctly will

Depending on the average firmness of the fruit you intend to ripen you can use temperature (for fruit 1.5 to 3.5 Kfg) or a combination of ethylene and temperature (for fruit >3.5 Kgf). In most cases, increasing the flesh temperature of the kiwifruit should be sufficient to effectively condition the kiwifruit.

You Need to Consider the Following Factors:

1) Ability to Warm and Cool Fruit

Only consider ripening fruit if you have coolstores with strong airflow and cooling capacity. These factors are essential to prevent fruit in the centre of the pallet remaining warm post treatment. If you have limited cooling capacity, then a more conservative conditioning approach should be followed- particularly if you are close to your target firmness.

To slow ripening down its important to get the fruit temperature back down to 0°C ±0.5°C as soon as possible. Depending on the cooling capacity of your coolstore to cool the center of your pallet may take 12-24hrs+. Always keep this in mind when determining how long to leave your fruit conditioning for.

Cooling capacity Pop up - It's important to know your heating/cooling capacity by plotting the results onto a graph and drawing a heating/cooling rate curve by connecting the data points. Calculate the heating/cooling rate by dividing each temperature data point by its corresponding time data point then average all of your answers to achieve a cooling rate. In other words, the change in the temperature divided by the change in time will give you an average temperature rate change.

2) Your Supply Chain

When setting your target firmness range, it is important to consider:

Your location in the supply chain (e.g. distance to end consumer)- Consider current overall fruit firmness and the time available before delivery to retail/next business to decide whether further ripening is required or if pallets need to be held in coolstore.

The End Retail environment (display temperature and sales rates)- Depending on the temperature of the shelf display the fruit will be stored on, you will need to adjust the targeted firmness. If fruit is going onto a display shelf of 30°C instead of 20°C then you'll need to set your target firmness higher, to ensure adequate shelf life to inventory turnover.

Inventory Turnover- Is your stock moving fast or slow? The slower the turnover the more cautious you should be with the amount of fruit you choose to ripen.

3) Fruit Variability

Variability of fruit firmness within the pallet- Pallets can contain multiple grower lines, which can result in increased fruit variability in the pallet. If certain grower lines are identified as being more variable then the target firmness for the pallet may need to be higher to prevent the softer lines being over-ripened. In some cases, it may be worthwhile segregating the firmer or softer grower lines and performing separate treatments.

Sample size and selection – The larger the sample size the more representative the sample will be particularly on variable fruit. If sampling 10 fruit per grower/pallet then it's important to select fruit that gives a good representation of the grower. Selecting fruit from at least 2 to 3 packs in different locations of the pallet is recommended. 

Ripening Tips

Establish ripening records – Your ripening records will become a great resource in helping you develop your ripening protocol. Different cultivars ripen at different rates, so it is worth keeping separate records for each cultivar to help you develop specific ripening models.

Start slow, learn fast – It is recommended when starting out to approach the ripening conservatively by not trying to ripen the fruit too quickly in too short a timeframe. Once experienced in ripening the approach can be pushed further.

Continually Monitor Your Fruit - As fruit ripens it's respiration rate accelerates, this causes the fruit to release more heat, further increasing its temperature. The key principle to ensuring your ripening programme is a success is continual monitoring. Frequent assessments will help you identify at what speed your fruit is moving as well as enabling you to respond quickly to any situation.

Ripening with Temperature

Whether you've decided to ripen your fruit using solely temperature, or have decided to use both temperature and ethylene, the key steps in either process are predominantly the same.

1) Take baseline measurements

Fruit Firmness - As detailed in the Assess section of the site, make sure you take a robust sample from all the grower lines within the consignment you'd like to ripen. It is strongly recommended that you take your sample fruit from various packs throughout the pallet. Following this assessment you may wish to segregate grower lines bases on firmness - Remember to maintain tractability!

Flesh Temperature – Always check that your flesh temperature of your fruit is in line with your storage temperature and if not take this variance into account when predicting your potential softening rates.

Room Temperature - Prior to ripening you'll also need to confirm the temperatures of your coolstore and ripening rooms. It is good practice to take several readings throughout the day so you can be confident in your measurements. Once you have confirmed these temperatures you can integrate this information into your ripening protocol as it will help estimate how long it will take to warm/cool the pallet. 

2) Warm up fruit – Remove from coolstore and place in conditioning room

Assuming you have sufficient re-cooling capacity the table below provides some guidelines for treatment temperatures and duration's for both Zespri Green and Zespri SunGold Kiwifruit.

Variety: Zespri Green & Zespri SunGold Kiwifruit

3) Monitoring the Ripening Process

Sample Frequency – We recommend to monitor your conditioning temperature as well as flesh temperature and firmness at least every 12hrs (The higher your assessment frequency the better). As you get closer to your desired firmness rnge you may want to increase the frequency of your assessments.

Softening Rate – Based on your measurements identify how quickly the fruit is softening and if needed adjust your ripening protocol accordingly. Always remember that it will take at least 12-24 hours to re-cool your pallet and during this time your fruit will continue to ripen quickly.

4) Re-cooling your fruit

Move quick - As you begin to approach your desired firmness range you will need to  think carefully about your ability to re-cool the pallet. Until such time as the entire pallet is back below 5°C the fruit will continue to ripen rapidly. Ensure you move your pallet back into cool storage as soon as possible.

Set a buffer - Knowing that it's going to take sometime for your fruit's temperature to reduce once you have placed it back in coolstore and that your fruit will continue to ripen during this time, it is good practice to allow yourself a buffer to account for this additional ripening. A safe buffer range could be 0.25-.5kgf above your desired target, depending on your re-cooling ability.

Ripening with Temperature 

Setting Temperature – This is dependent on several factors. If you're an inexperienced fruit conditioner we recommend not going above+10°C particularly if you don’t have forced air cooling/heating.

• The gap between your current fruit firmness and target firmness, as well as the time available to you before delivery. A slower ripening process is less risky, allowing more time for your fruit to ripen and will also be less likely to negatively impact the fruit quality.

Tip: While your expertise is growing through time, you will be able to add additional fields in your monitoring template such as expected cooling rates and predictive firmness ranges.

Link to Excel Template – Stu to provide 

• Monitoring resources – Make sure you're able to assess, record and decide appropriate actions every 6 to 12 hours.

• Facilities exeperience and confidence level – As you become more experienced with ripening kiwifruit you will be able to refine you ripening regime and potentially perform ripening with increased temperatures and shorter timeframes.

Ripening with Temperature and Ethylene

Kiwifruit are very susceptable to the effects of ethylene. Even at concentrations as low as 0.1ppm at 0°C for several days, considerable softening occurs.

Relatively short periods of exposure to ethylene are sufficent to trigger flesh softening. Depending on the range of firmness and the average, a ripening programme can be determined. Broadly speaking, the softer the fruit the shorter the exposure to ethylene required, if at all, and the lower the temperature.

The programme should aim to give fruit suitable for delivery at about 1.5kgf average after at least three days of ripening.

POP UP WINDOW

If the ripening needs to be sped up, ethylene can be used along with elevated temperature. Ethylene will help develop flavours and more consistency in firmness, but comes with higher risk.

1. Gas with ethylene @100ppm (the total volume of gas required will be dependent on the size of the ripening room and volume of fruit for smaller applications a XX second burst of ethylene at X pressure should be sufficient.

2. Hold gas for 12 hours. Monitor CO₂ levels.

3. Keep airflow high.

4. Vent for 6–12 hours. 

5. Measure fruit firmness and flesh temperature, then hold for 24 hours before monitoring fruit firmness and flesh temperature again.

Required rate and calculating ethylene requirements

The following tables are suggested guides, depending on events up to arrival at ripening plant. It is based on the single shot method and ripening rooms using forced air.

Note: SunGold softens initially more rapidly than Zespri Green and needs to be treated as such.

Total conditioning times may vary depending on softening rate after ethylene treatment by measuring initial firmness to current firmness taken at least every 12 hours.

If the fruit is not cooled after ripening it will continue to soften.

Cooling to 0°C will slow down the rate of softening.

• Fruit at 3.0Kgf to 3.5 kgf, held at 20°C without ethylene will probably soften to 1.0Kgf in about six to seven days. There will probably be some variation in firmness, but this may be acceptable in a fruit with slower rate of softening.

• As a genreal rule of thumb, apply ethylene @ 100ppm for 30 seconds, per cubic meter.

VARIETY: Zespri Green & Zespri SunGold Kiwifruit

Step 1 – Warm up the fruit

For ethylene to work effectively you need to warm up the pallet to treatment temperature before you apply the ethylene treatment.

Allow approximately 12–24hrs for the fruit to reach your target flesh temperature.

Step 2 – Release Ethylene

Once the fruit have reached the targeted treatment temperature, ethylene can be introduced into a room in two ways:

• Ethylene single shot method

• Ethylene flow-through or trickle method

We are focusing on the single shot method to keep things simple. For smaller volumes it is also possible to cover you kiwifruit in a shroud. The shroud will need to be airtight, which can normally be achieved by taping it to the floor.

Ethylene single shot method

In the single shot method a mixture of ethylene gas is introduced into the room in an accurately measured quantity. A pressure regulator and flowmeter are used to control and monitor the flow of ethylene into the room.

With the single shot system the conditioning room is sealed during ethylene treatment and therefore CO₂ accumulates in the room, and this may inhibit the ripening process*. This will not usually be an issue for treatment times of 12hrs or less, but may be something to consider if you decide to administer a longer ethylene treatment.

*CO₂ above 4% the effectiveness of ethylene will be reduced.

Step 3 – Vent Room

Following the successful treatment of your fruit the next step is to allow the consignment time to vent. It is at this time you would flush the room with clean air or simply remove the shroud. It's good practice to give the fruit sufficient time to vent 4-12 hours depending on the size size of the consignment.

Handy tips for successful ripening

Please note that when using ethylene to ripen the fruit extra care needs to be taken. Please follow the below guidelines:

• Fully vent fruit for a number of hours before storing with other inventory.

• Maintain air circulation throughout ripening.

• Use forced air warming and cooling to reduce temperature differences across pallet (core).

• Maintain high humidity around fruit by keeping packs closed.

Step 4 – Continue Temperature Treatment

Now that your fruit's ripening process has been triggered by the ethylene treatment (and all the ethylene has been successfully vented) you now need to ensure your fruit remains at the desired temperature for the remainder of your treatment phases. Remember to regularly assess your fruit every 6–12 hours to ensure the fruit is tracking as per your ripening regime.

Step 5 – Recooling the pallet

Once you have reached the targeted firmness, you will need to cool down your pallet and return your fruit to the desired storage temperature (1°C).