Temperature control alone as post-harvest treatment not sufficient

High humidity post-harvest slashes quality claims for grape grower

Two years ago Johan Kriegler, CEO of Kriegler Farms in the Hex River Valley, decided to bring a change to their table grape holding rooms, to give the best possible post-harvest treatment to fruit that had received the best possible treatment in the vineyard.


Johan Kriegler with a bunch of SugraOne (Photo by Louise Brodie)

He had four units of Miatech’s Aquaroom 4S humidification system installed to increase the relative humidity in the holding room to 95% where grapes are kept at 20°C. The reason for the high relative humidity is to reduce the humidity gradient between the grape and its surrounding atmosphere. If the latter is drier than the grape – which it inevitably will be in South Africa – moisture is drawn along the gradient out of the fruit into the atmosphere, and post-harvest decay starts.

Kriegler Farm gets its harvested grapes into the holding rooms within 12 to 20 minutes in order to start the post-harvest treatment as soon as possible. It is supplemented by four units of the BIOTurbo 300 filter that removes ethylene, bacteria and fungal spores from the atmosphere.

Because of the high relative humidity of the holding rooms, extraneous vegetative parts can be cut from the bunches the evening before without any drying-out of stems, so that packing can start straight away the following morning and less time is lost. “The secret is to cut the grapes as soon as possible. In the past grapes started drying out in the holding rooms but now we can keep grapes there for longer and with better results,” Kriegler explains. “Also, when stems remain green, there’s no chance of infection developing between the stem and the berry.”


BIOTurbo air filter in a holding room

Jan Lievens of Miatech describes the harvesting process as cutting the umbilical cord of the bunch of grapes. “Leaving it overnight to reach temperature settles the grapes down, they’re not so stressed when in a high humidity atmosphere.”

After packing, grapes go to the Hexkoel storage facility where they are chilled to -0.5% for a period of 24 to 30 hours.

“This has been our second packing season with this technology and we have seen a big improvement in quality. Quality claims have come down significantly. There have been no quality claims from Woolworths this year and while it’s still too soon to speak for the export markets, we can see that the quality looks really good and our stems are much greener,” says Johan Kriegler.

Furthermore, he had a BIOTurbo 100i air filter installed in the reefer truck that transports the grapes to Woolworths, the first farmer in Africa to do that and as yet, still the only one.

Kriegler Farms markets its grapes between South African retailer Woolworths and UK supermarkets like Marks&Spencer, Sainsbury’s and Tesco on a 50-50 basis. According to David Cuff, chief fresh produce buyer for Woolworths: “Kriegler Farms is a key part of our supply. We get about 25% of our grapes from them.”

Exports to the UK make up 87% of Kriegler Farm’s exports and this year they sent, for the first time, two containers to the USA. “I prefer marketing to the retailers because I know I will get my input costs back and it reduces risk. I’d rather take a lower profit margin but I know what I will get. Last year we did very well on the UK market, when the Rand was R21, R22 to the Pound. This year it’s about R16.50 to the Pound, but we’ll still make a profit. The other advantage to the UK market is that the grape price there is quite constant,” says Kriegler.

Four years ago the farms – its operations are run over two farms in the same area, Kleinberg and Klipheuwel – still had a large proportion of seeded grapes but today, following market trends, it produces 100% seedless grapes. Kriegler says that they invested heavily in new cultivars. “We’re very happy in general with our cultivars like Sweet Celebration from the IFG range, the Sheehan varieties and then the older ones like SugraOne and Crimson. The only variety that didn’t work for us is Autumn Royal and we removed those blocks.”


Klipheuwel farm (Photo by Louise Brodie)

Jan Lievens believes that temperature control addresses only part of the post-harvest requirements. “Humidity and temperature together are particularly critical in minimising the difference in water vapour pressure between the produce and the environment. The humidity of the surrounding environment should be maintained at a level that minimises the water vapour pressure deficit.”

He continues: "An un-cooled table grape at 32°C deteriorates in an hour as much as in a day at 4°C or in a week at 0°C. In South Africa applied post-harvest technology is still undervalued. Farmers spend 95% of their time and money on the growing process, and they get fantastic product – our farmers are some of the best in the world – but when it comes to the last 5%, they neglect that part. The research overwhelmingly shows that relative humidity plays a critical part and you can’t just douse the fruit with water, it must be dry humidity, otherwise you end up with disease and spoilage on wet fruit.” He states that the farmer’s job only ends when the product has been purchased, wherever in the world that may be.

Miatech’s technology is increasingly employed among table grape growers in Chile and Peru by companies such as El Pedregal from Peru, as well in Chinese warehouses where BIOTurbo filters are gaining in popularity. The Aquaroom humidification system has been in use for thirty years.

For more information:
Johan Kriegler
Kriegler Farms
Tel: +27 23 357 9802


Jan Lievens
Miatech/Umhwebo Trading Enterprise
Tel: +27 78 992 2485

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