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  • Jan Lievens

Berry Blues

Some people think they will find their thrill on Blueberry Hill and it is still amazing to see that often companies when dealing with fine tuning Postharvest procedures in general, tend to not pay attention to detail. They have spent a fortune on cooling and that is it: NO MORE. Think again.

Preserving quality after harvest does not come by chance and attention to detail is of the utmost importance.

This should become part of the daily thought process of anybody involved in fresh commodities.

Attention to detail also means talking to the right professionals. Do not just go on price, do not get fooled by “it’s cheap, it will be good enough” … It often is not, talk to people with a track record, but still do not forget to look at all aspects of your postharvest projects.

This of course doesn’t mean you do not have to look at cost, but balance it, weigh it off to the losses and you will find out that the real McCoy is often far cheaper in the long run than what you would think.

I do not know if it is through the Covid-19 pandemic, but it seems to me that the fly by nights now also fly by day…

Attention to detail in postharvest is often simply overlooked. When visiting a farm recently, I noticed that often people are still chasing symptoms in postharvest instead of tackling and handling root causes.

When walking into a room full of fresh crisp blueberries, I couldn’t help observing that somebody put, rather unsuspecting and not aware of any possible harm that could get caused, a pallet with bacteria loaded clementine’s in the same cold room. None of the quality inspecting guys did notice. Once more, attention to detail and proper training of operators is beneficial…

Depending on your commodity, details like that could be detrimental and often leads to huge losses…

A lot of hype explodes sometimes on certain commodities at any given time. Berries being one. As you all know, the number of hectares planted in South Africa is astronomical.

Berries are very perishable and maintaining fresh quality after harvest depends on proper handling, transportation, and storage.

Harvest dates and time is determined by berry surface color. More than ½ of the berry surface should be colored, depending on the grade and berry type. All berries should be harvested near ripe, as eating quality does not improve after harvest. Appearance, i.e. color, size, shape, and freedom from defects, firmness, flavor, i.e. soluble solids, titratable acidity, and flavor volatiles and nutritional value (vitamin C) are all important quality characteristics.

Then you harvest and then the attention to detail kicks in. And besides timing, ethylene management is being one of them. Ethylene does not stimulate the ripening of strawberries, raspberries, and blackberries. Therefore, these berries should be harvested near to full ripe.

Blueberries however are climacteric fruit and will respond to ethylene.

Nonetheless, blueberries should also be harvested near to full ripe because flavor does not improve after harvest.

Proper removal of ethylene from storage air may reduce disease development in all berries.

Precooling (rapid removal of field heat) is essential preferably within ½ to 1 hours of harvest. For example, strawberries maintained at 10°C have about one-third the storage life as those rapidly cooled down to 0°C.

Precooling may be accomplished by forcing rapidly moving properly humidified cold air through stacks of berries with forced-air cooling.

Still, an optimum dry humidity of 90-95% RH should be present always during this process. With dry humidity we mean that no water should ever be splashed on the berries and working with open unclean water will just aggravate disease.

And never forget this golden rule: fruit does not respond well on irregular temperature changes and gets damage if you do. Once you cool, keep it at the same temperature.

Your precooling temperature should be the same as your packaging temperature.

Optimum storage conditions for strawberries (7‑10 days), blueberries (2‑4 weeks), raspberries and blackberries (2‑5 days) are 0°C and 90‑95% relative humidity. Cranberries (2‑4 months) are chilling sensitive and therefore, should be stored at 3°C.

But remember, in general, storage-life is very dependent on the handling of berries during and after harvest. Again, attention to detail.

The highest freezing point is ‑0.8°C for strawberries and blackberries, ‑0.9°C for cranberries, ‑1.1°C for raspberries, and ‑1.3°C for blueberries. Overall, berries with high soluble solids content are less likely to freeze.

Berries are very susceptible to water loss, which results in fruit shrivelling and loss of gloss. You lose marketability very quickly.

Furthermore, diseases are the greatest cause of postharvest losses in berries. Prompt cooling, storage at the lowest safe temperature with the correct RH levels, preventing physical injury to the fruit, and shipment under high carbon dioxide (10-15%) are the best methods for disease control, but are not enough. In addition, care should be taken to keep diseased or wounded berries out of packages, as rot can spread from diseased to nearby healthy berries. But unfortunately, that is even not enough, proper, and proven ethylene and airborne bacteria removing equipment will avoid lots of quality issues in the process.

Gray mold (Botrytis cinerea) can be a serious problem in berries. This disease can develop during storage if fruit has been contaminated though harvest and handling wounds. Avoiding mechanical injuries and good temperature management are effective control measures. This fungus continues to grow at 0oC, albeit growth is slow at this temperature.


Rhizopus rot (Rhizopus stolonifer) can also be a problem in berries. This fungus forms a fluffy, black whiskery mold on the fruit surface. Cooling the berries and keeping them below 5°C is amazingly effective against this fungus, since it will not grow at these temperatures.

Still feeling you should forget about details and chase symptoms rather than the root causes?

Think again, Fats Domino maybe found his thrill on Blueberry Hill, you will lose your profits and remain with the shivers Berry Blues…

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