Kiwi Yield, Harvest, and Storage

Kiwifruit, known for its vibrant green flesh and unique flavor, is a consumer favorite and a valuable crop for farmers worldwide. In 2023, global kiwi fruit production was approximately 4.5 million metric tons. China, Italy, New Zealand, Iran, and Greece were the major producing countries contributing to this. Approximately 70-75% of the total production was green kiwis, 20-25% were golden kiwis, and only 1-5% were red kiwi fruits. The USA, Germany, China, Japan, and Spain are the biggest countries that import kiwifruit. Kiwifruit requires careful attention to maximize yield potential and ensure optimal harvest timing. At the same time, appropriate storage will help preserve the fruit's superior quality for extended periods and satisfy market demand.

Yield of Kiwi Plants – How much kiwi yields per hectare?

Kiwi plants are highly productive when grown under optimal conditions, including suitable climate, soil, appropriate training, and cultivation practices. More specifically, a kiwi plant/vine can produce, on average, 50-100 kg (110-220 lbs) of fruits. Several factors can influence the yield potential of kiwi plants. The farmer is advised to study and understand them to sustainably maximize the crop yield and fruit quality. The most important are:

Variety: Different kiwi varieties, such as Hayward (green), Zespri Gold, and the newer red varieties, have different yield potentials. Green kiwifruit typically has higher yields than the gold or red varieties. More specifically, Hayward, the most popular variety of green kiwi, can yield, on average, 20 to 45 tons per hectare (17844-40148 lbs/acre). Yellow or Gold Kiwifruit, using the Zespri Gold variety as an example, can yield 15 to 20 tons per hectare (13383-17844 lbs/acre), while red kiwifruit varieties have a lower yield potential of around 10-15 tons per hectare (8922-13383 lbs/acre).
Environmental Conditions: Ideal conditions include a temperate and frost-free climate, fertile and well-drained soil, and adequate water. Extreme cold can damage the vines and reduce fruit set, while excessively high temperatures can lead to sunburn and affect fruit development. Frost during the flowering period can severely impact yield by damaging flowers and young fruit. High humidity levels increase the risk of fungal diseases such as botrytis, which affects fruit quality, storage life, and commercial value.
Management Practices: Proper pruning, training, and canopy management are essential for maximizing light exposure and fruit production. More specifically, green kiwis can reach higher yields when trained with the pergola and Geneva Double Curtain Systems (giving 30-50 tons per hectare or 26765-44609 lbs/acre). These two systems offer a better yield than the T-bar system primarily due to better light management and space utilization (however, they are more expensive and labor-intensive). Also, proper training (especially the pergola system) enhances fruit quality by ensuring even ripening (even exposure to sunlight and good aeration), improving size and sugar content, and reducing disease infections. Improved accessibility for maintenance practices further supports the production of high-quality fruit. Nutrient management, pest control, and pollination are also critical components. Deficiencies or excesses of nutrients like potassium and calcium can affect fruit size, firmness, and taste. Some kiwi growers apply phytohormones (e.g., CPPU product, 3 weeks after flowering) and potassium to increase fruit weight. Due to weather conditions, poor bee activity, and poor pollination can result in poor fruit set and misshapen fruits. Finally, water stress can lead to smaller fruit sizes and reduced yield, while over-irrigation can cause root diseases.

Determining the Right Harvest Time for Kiwifruit – When to Harvest Kiwifruits?

Kiwifruit maturation is a complex process influenced by genetic and environmental factors. The fruit typically takes around 150-180 days (depending on the variety and location) from flowering to reach maturity and be ready for harvest. Farmers must carefully monitor several indicators to determine the right moment for harvesting:

Dry Matter Content (DMC): DMC is a crucial factor in determining the harvest readiness of the kiwi fruits. For green kiwifruit, a DMC of around 15-19% is often used as a benchmark for harvesting, while gold varieties may be harvested at slightly lower DMC levels.
Soluble Solids Concentration (SSC): SSC, often measured in degrees Brix, indicates the sugar content of the fruit ( total carbohydrate concentration). A minimum Brix level, typically around 6.2-6.5, is required for kiwifruit to ensure sweetness and flavor post-harvest. The different markets may set their minimum acceptable limits that can be quite higher than the ones indicated here. It is interesting to know that green kiwis should have around 12-13 °Brix and golden kiwis up to 18-19 °Brix for pleasant consumption. Green kiwis with Brix lower than 6.2 °Brix are illegal to be marketed. Farmers and traders are strongly advised to check all requirements when they consider entering a new market. A refractometer can be used to test the SSC.
Firmness, Color, and Size: As kiwifruit matures, it changes skin color and firmness. The skin color changes from bright green to a more yellowish hue, and the fruit becomes less firm to the touch, signaling ripeness. Green kiwis that suffer from iron deficiency are expected to have less commercial value. Size is also an important factor. Bigger fruits can obtain higher prices.

Harvesting Techniques for Kiwifruit – How to Harvest Kiwifruits?

Harvesting kiwifruit is a labor-intensive process that requires careful handling to avoid damaging the fruit. The following techniques are commonly used in commercial kiwi orchards:

Manual Harvesting: Most kiwifruits are harvested by hand to minimize bruising and ensure the fruit remains of high quality. Workers use clippers to cut the fruit from the vine and place it into bins or crates placed on top of crates to reduce the height at which the fruit is dropped. Harvesting the kiwis is easier in orchards with a pergola training system. In some regions, mechanical aids such as platforms and conveyor belts are used to assist workers in collecting the fruit, increasing efficiency while maintaining careful handling practices.
Mechanical Harvesting: While it is not used in kiwi orchards today, the development of autonomous kiwi harvester is emerging as a strategic necessity for large producers. Currently, New Zealand, Italy, Chile, and China carry out research into the mechanism of kiwifruit production (scaffolding cultivation).

Kiwi Yield, Harvest, and Storage

Post-Harvest Handling and Storage of Kiwi Fruits – How do Kiwi fruits be stored?

Once harvested, kiwifruit should be quickly removed from the field (sun and heat) and transported to packing facilities, where it undergoes sorting, grading, and packaging. Proper storage conditions, including controlled atmosphere storage, are crucial to extending shelf life and maintaining quality. The key objectives during post-harvest handling are to minimize physical damage, maintain freshness, and prevent spoilage. One of the strong advantages of kiwi fruits is that they can be stored for several months (in some cases, even up to 10-12 months) under optimum conditions. For this reason, it is essential to take all necessary measures to accomplish this and satisfy consumers' expectations.

Grading of Kiwifruits

Kiwifruit is graded based on size, shape, and external appearance. The grading process involves sorting the fruit according to set standards, which helps determine the market price and quality classification. In the United States, the USDA has established specific grading standards for kiwifruit:

U.S. No. 1: This grade requires the fruit to be of similar varietal characteristics, fairly well-formed, and free from decay, damage, and sunscald. Minor skin defects are permissible, provided they do not affect the overall quality.
U.S. No. 2: Kiwifruit in this category may have more pronounced defects but must still be free from decay and severe damage.

Internationally, the Codex Alimentarius Commission provides guidelines for kiwifruit quality. These standards emphasize uniformity in size and shape, firmness, and minimal blemishes.

Based on their size, kiwifruits are classified as:

Small: Less than 90 grams or 0.2 lb /fruit.
Medium: 90 to 110 grams or 0.2-0.24 lb /fruit.
Large: 110 to 130 grams or 0.24-0.3 lb /fruit.
Extra Large: More than 130 grams or 0.3 lb/fruit.

Storage Conditions for Kiwifruits

Proper storage is vital to prolong the shelf life of kiwifruit and maintain its quality. Kiwifruit is quite demanding and sensitive when it comes to storage conditions. It is essential not to break the cold chain (no temperature fluctuation) throughout the storage and transportation of the product. Specifically, kiwifruit should undergo precooling (e.g. hydrocooling) as soon as they arrive from the field and go to the storage unit (especially when the temperatures during harvest are relatively high). After this treatment, the fruits should be stored at temperatures between 0°C and 1°C (32°F and 34°F) to slow down ripening and prevent spoilage. A high relative humidity of 90% to 95% is ideal to prevent fruit dehydration. Kiwi fruits are very sensitive to ethylene, and storage units with a controlled atmosphere are required. The ethylene produced by the fruits should be removed constantly from the storage units while at the same time reduced oxygen levels and increased carbon dioxide can further extend its storage life by reducing respiration rates and delaying ripening. During transportation, kiwis should not be placed on the same truck as fruits producing high amounts of ethylene (e.g., bananas or pears).

Kiwi Yield, Harvest, and Storage

Kiwifruit Quality Standards

Quality standards for kiwifruit emphasize size, shape, firmness, and lack of defects. Critical indicators of high-quality kiwifruit include:

Firmness: The fruit should be firm to the touch, indicating it is not overripe.
Uniformity: Consistency in size and shape is essential for consumer appeal.
Lack of defects - Minimal blemishes: The skin should be free from significant blemishes, bruises, or signs of decay.

Packaging Options for Kiwifruit

Packaging is essential to protect kiwifruit during transportation and storage. It also plays a role in marketing, branding, and presenting the fruit to consumers. Packaging sizes and types can vary significantly between different markets and retailers. Some regions may prefer smaller, consumer-friendly packaging, while others might favor larger bulk packages for wholesale or institutional buyers.

Common packaging options for kiwi fruits include:

Retail Packaging Options

Plastic Clamshells: These are popular for retail sales as they provide protection and allow consumers to see the fruit. They also facilitate stacking and display. They typically hold 450 to 900 grams (1 to 2 lb) of kiwifruit or 4-8 kiwis (of around 90-110 grams each).
Net Bags: An eco-friendly option, net bags allow for breathability and are often used for smaller quantities intended for immediate consumption. They usually contain 900 grams to 1.4 kg (2 to 3 lb) of kiwifruit or 8-12 medium-sized kiwis.

Bulk Packaging Options

Fibreboard Trays/Cartons: These trays provide cushioning and are often used in combination with plastic liners to maintain humidity levels. The standard cartons weigh between 7 to 10 kg (15 to 22 lb) and may contain 90 to 130 kiwifruits (of 110-140 g weight each).
Corrugated Cardboard Boxes: They have a function/characteristics similar to fibreboard trays and can typically hold 10 kg (22 lb) of kiwifruit or 100 to 120 large fruits.

By adhering to the quality standards mentioned above and implementing effective post-harvest handling practices, producers can ensure that kiwifruit reaches consumers in optimal condition, enhancing satisfaction and marketability.