By Jan Lievens
This is one statement of Albert Einstein. He was, and is still right.
When you understand nature, you will understand what is happening with and in certain postharvest processes. The sooner you understand that you are working with living material, the better.
As I have said many times before, nature never ever breaks her own laws, not yesterday, today, or tomorrow.
To understand this matter and statement fully, one must understand that fresh produce and horticultural commodities are unique packages of water! In fact, freshness is water, and freshness is what sells!
Water loss is one of the main causes of deterioration that reduces the marketability of fresh fruits, vegetables, and flowers. Profitability in sales of these products ultimately depends on the ability to deliver as much of this water as possible to consumers, in good condition.
The effects of water loss are devastating.
Many fruits, vegetables, and flowers become shrivelled after losing only a small percentage of their original weight due to the water loss factor. Severe desiccation results in considerable water losses, for example- wilted leafy vegetables may require excessive trimming to make them marketable, and grapes may shatter loose from clusters if their stems are severely dried.
Seriously shrivelled fruits, vegetables, and flowers become “unmarketable” or “unsaleable” and therefore must be discarded – which further adds to global food losses.
Water loss represents saleable weight loss, and therefore reduced profits
The factors that affect water loss are relative humidity (RH), the temperature of the product and its surrounding atmosphere, and air velocity. All of which are well documented while some are more often a forgotten area.
All of these affect the amount of water lost from fresh produce and flowers. Water loss from warm products to warm air is particularly serious under windy conditions or during transport in an open vehicle.
Maintaining high relative humidity is sometimes difficult because refrigeration removes moisture. Professional and controlled humidification should therefore be used in pre-coolers and storage. And I must add – please, stop believing the myth that your cold rooms are designed to maintain high humidity – this is not accurate.
Measure your starting RH at the beginning of the process and start thinking. Cheap and nasty solutions like keeping the floor wet are helpful but are also messy and may harbour disease-organisms or organisms from old produce on the floor. And that is the least of what you should want – you must simply refer to what happened in Europe in 2011 to fully understand that you don’t really need these kinds of things to get into your products.
In most cases, direct water application to fresh produce and flowers must be avoided as a mechanism to control humidity levels. Here, these two photographs illustrate the effect of photography on the perception of produce quality. Both are equal products, the one with droplets however gives the impression of being ‘more appealing’.
Also, something to remember is that molds grow the best above 4°C and above 60% humidity. So, if your processes flow asks to precool at 17–22°C at 95% RH, pay due diligence in keeping your walls and floors clean, always!
Therefore, frequent sanitising procedures should be employed, such as cleansing frequently and rinsing with a weak solution of chlorine bleach. Commodities that can tolerate direct contact with water can be sprinkled to promote high relative humidity. But in most cases, direct water must be always avoided. Except for the photographers of course that want to take nice pictures and water droplets lead most people to think the product is fresh and clean and appetising…
Bottom line, you can research all you want, the subject is well documented by many researchers worldwide, hence the huge reference lists that are available on request. Once you understand nature, it is easy. It is fun to see that by respecting nature and its laws, you really get perfect results every time in maintaining shelf life.
Talk to the right people that have proved their mettle by implementing the right methods, at the right time, because they understand mother nature.
About Jan Lievens
Jan Lievens, born in Belgium, is a graduate civil engineering(B) and international senior consultant for engineered applied postharvest technology at Humiditas South Africa. With over 20 years of experience in this field, he is widely regarded as a specialist in the fruit-, vegetable- and flower industry with regards to humidity, airborne bacteria and ethylene removal, both locally and internationally. Furthermore, he also designed airflow-friendly packaging systems for the industry with proven results.
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