Objective colour assessment for dried grapes now a reality

With fruit colour determining the price dried grape growers are paid, developing a reliable way to objectively measure this aspect of the product has long been a goal for the industry. Now two feasible options have been put forward, both based on quick and easy photographic analysis.

Currently the grading of dried grapes is done wholly by the human eye. While graders are very good at what they do, the fact that there is a level of subjectivity means disputes can and do arise between growers and processors – with significant dollar differences riding on the outcomes.

Hort Innovation Chief Executive John Lloyd said that while determining the lightest, highest-grade dried grapes and the very darkest fruit is typically clear-cut, it’s over the intermediate grades that dried grape growers and processors can sometimes disagree.

“It’s for these situations that an objective way of analysing fruit colour and determining grade has been needed,” he said. “Instigated due to advances in technology and a need to get this solved, two Hort-Innovation-funded projects have each looked at a number of options for objectively measuring dried grape colour. Now concluded, both projects have arrived at image-analysis methods to help take uncertainty away in those ‘greyer areas’ of grading, for the benefit of both growers and processors.”

The first approach involves the use of a scanner and computer algorithm. It was developed as part of a project led by Dr Jenny Ekman at Applied Horticultural Research.

“The method uses a simple flat-bed scanner, the same that anyone might have in their office,” Dr Ekman said. “You literally put a handful of sultanas onto the scanner, the scanner is connected to a computer and based on the scanned image a software program – developed by the Central Queensland University – tells you what grade the batch is.”

Dr Ekman said that this objective colour-assessment approach is quick and easy for operators, and consistently reliable. “The advantage of using a scanner is that you put the fruit in, close it up and there’s a standard light source analysing the dried grapes in a single layer. The colour analysis isn’t being affected by any outside conditions, and multiple scoops from the same bins will give the same answers every time.”

The second method of measuring dried grape colour objectively involves the use of a custom-built ‘lightbox’, developed as part of a project led by Dr Vinay Pagay at The University of Adelaide.

“While not unique, our solution is a first for the dried grape industry,” Dr Pagay said. “We’ve designed an imaging box with 3-D custom-printed trays. You load the dried grapes into trays inside the box, the box is connected to a digital imaging camera, and then the software we’ve developed does the image processing. It counts the fruit, does a colour analysis, and gives a suggested classification, giving an objective approach to establish grading.”

Dr Pagay said the approach is fast, simple and relatively inexpensive, too.

Importantly, both Dr Ekman and Dr Pagay said neither tool was about giving graders’ jobs to computers.

“Objective colour assessment is something really to be used as a back-up, when growers and processors can’t agree on a colour grade,” Dr Ekman said. “That could involve a fair percentage of what’s coming in, though – maybe a third or even half of the bins might need to be sampled.”

During September both tools were tested at Sunbeam’s facility in Red Cliffs, Victoria, with great results in terms of usability and consistency, and some minor tweaks identified to ensure the approaches deliver what the industry needs.

A rundown of the tools will be presented at an upcoming meeting of Dried Fruits Australia, and Hort Innovation’s dried grape Strategic Investment Advisory Panel will ultimately consider the final reports of both projects to see what, if any, further work may be done to advance these technologies.