The pack-house perspective on internal browning

South African apples already compete successfully in international markets. How can the industry further improve fruit quality? By Anna Mouton.

The experiences of some growers during the recent season again demonstrated how even slight post-harvest defects can lead to significant financial losses when fruit are rejected on arrival at markets.

“These are losses that occur at the most expensive time possible,” says Henk Griessel, quality assurance manager at Tru-Cape. “You’ve incurred all the production costs, and storage, packing, and transport costs, plus taxes and insurance.”

Griessel explains that a warm season can contribute to internal browning if growers harvest fruit later in the hope of achieving better colour or larger fruit. “The standard for Pink Lady isn’t 100% colour, but every grower would like his fruit to have 100% colour — it’s only human.”

Unfortunately, maturity can become too advanced while one waits for colour development. Post-optimal maturity — indicated by increased starch breakdown — is a key driver of internal browning in both Cripps Pink and Fuji. “Harvest maturity is super-important in Pink Ladies,” stresses Griessel. “You can’t play around with that.”

According to Griessel, it has become more challenging to pick fruit at their optimal maturity, as high labour costs motivate growers to try and save on harvesting. Growers have to weigh the cost of additional handling of fruit that may have different maturities against the risk of losses due to internal browning and other post-harvest disorders.

Besides harvest maturity, the conditions under which Cripps Pink apples are stored and transported are critical. Research has shown that these fruits should never be kept below 0°C. “This is important research that isn’t always known to logistical people,” says Griessel. “We need to invest more time in reaching those guys.”

Fundamentally different Fuji

Internal browning in Cripps Pink and Fuji are fundamentally different, explains Jaco Moelich, general manager of technical services at Fruitways. “My experience is that browning in Fuji is caused by high CO₂ levels in the fruit. Cripps Pink can also get CO₂ browning, but the frequency in Cripps Pink is low.”

Orchard factors play a role in both Fuji and Cripps Pink, but according to Moelich, Fuji browning is far more orchard specific than Cripps Pink browning. “In a bad season, browning will be fairly widespread in Cripps Pink, and then there won’t be any browning the following season,” says Moelich. “Whereas Fuji browning tends to repeat far more in the same orchards over seasons.”

Certain factors, such as large fruit, vigorous growth, low crop load, high nitrogen levels, and wet conditions shortly before harvest, can exacerbate post-harvest disorders in general. Sandy soils sometimes increase risk, especially when irrigation during heat waves is insufficient. As diffuse browning in Cripps Pink is linked to maturity, climate, microclimate, and orchard factors that speed up maturation will make browning more likely.

Although just about anything that increases stress also increases the risk of internal browning, Moelich points out that overly wet soils shortly before harvest are known to be associated with browning in Fuji.

“We have post-harvest protocols that help a lot, but in some orchards the risk is so high that you can’t prevent the problem entirely by applying good post-harvest practices,” says Moelich.

It isn’t possible to export high-risk Fuji apples, because CO₂ browning develops within 8–12 weeks after harvest. Modern pack houses rely on non-destructive in-line sorting technology to remove affected fruit on the pack line.

Luckily good post-harvest practices make a big difference to fruit quality in most cases. Stepwise cooling is an essential tool for managing internal browning in both Fuji and Cripps Pink, regardless of the different causes of browning in the two cultivars.

Greater grower engagement

“I just want to say that the research done over the years has helped our industry tremendously to refine our protocols around these issues,” states Moelich. Although not everything applied in South Africa was discovered here, local researchers have tested and adapted international methods for South African conditions.

“We can manage our risks fairly well, thanks to our knowledge of the research, some of our post-harvest practices, and through good orchard information,” says Moelich. “Internal browning is at very low levels in most years — it’s a minority of orchards that repeat with the problem.”

However, there is of course always room for improvement. Moelich believes that many post-harvest problems would be better addressed by adopting an integrated approach between preharvest and post-harvest. He illustrates this point with reference to internal browning in Fuji.

“The answer to managing internal browning in Fuji lies 25% in post-harvest but 75% in preharvest. But do we have a sufficiently integrated approach to the whole process, to find the connection between the two? To find the solution is difficult, but I think that, as an industry, we can try to do it better.”

“In the days when I joined the industry, growers were keenly interested in post-harvest, and in how they could land the best product,” recalls Griessel. “All the producers were very involved in the different post-harvest committees. Now there aren’t any growers on the post-harvest research committees — that’s not right.”

Griessel points out that most apples spend more time in cold stores and on ships than on trees. Cold stores and packhouses might not be the most fun places, and problems with delays and shipping can be frustrating, but post-harvest processes have an enormous impact on income.

“Post-harvest is the domain of engineers — you’re talking about controlled-atmosphere storage rooms and machines — but it should actually be the domain of producers,” says Griessel. “At the end of the day, these are their fruit. They are the ones taking the risks, so I’d like to see them becoming more involved.”

In the early days of controlled-atmosphere storage, South Africa was a world leader in this field, and this was producer-driven, according to Griessel. In the late seventies and eighties, growers even built their own controlled-atmosphere rooms. “They wanted to be the best, and to store their apples for a long time, so that they could make more money.”

The trend toward planting new apple cultivars will increase the complexity of post-harvest management. A cultivar planted in South Africa will yield a different product than the same cultivar planted in for example New Zealand or Europe, due to our unique climate. “Our growing conditions are different, so the fruit differ internally – cell structure, sugars, respiration, are all different,” says Griessel. “You can’t simply apply a European or American post-harvest protocol.”

Fortunately, good post-harvest protocols are already available for many cultivars, and can be obtained from the Hortgro website. But Griessel says that there are still many unasked and unanswered questions. His hope is that growers will take a renewed interest in post-harvest practices, to the benefit of the whole industry.