Vineland, Ontario – Postharvest specialists at Vineland Research and Innovation Centre (Vineland) have found a way to extend the shelf life of fresh Ontario table grapes so they can be available to consumers longer.
Sovereign Coronation is the most popular table grape variety grown in Ontario and it is ripe and ready for market in late summer and early fall – the same time as many other local fruits, as well as table grapes from other jurisdictions.
This means Ontario table grapes are often overlooked by fruit buyers and farmers face losses if they are unable to find a market for their crop.
“It’s a huge loss for growers if they’re not able to sell their crop, which is what happened in Ontario in 2011,” explains Kimberley Cathline, Senior Research Technician in Postharvest Science at Vineland. “That’s why we’ve been looking at postharvest storage so we can extend the marketing season and bring these grapes to market later in the fall when the saturation is over.”
The current storage life of Coronation grapes is about two weeks; as they lose water, the stems brown and Botrytis, commonly called grey mould, develops, causing the fruit to rot. The fungus can survive at almost 0°C, so it can grow even on grapes housed in cold storage.
Vineland’s postharvest team looked at what was being done in other parts of the world for a solution that could be adapted to Ontario’s fresh grape industry. They found sulphur dioxide, a naturally occurring compound that maintains fresh stem colour and limits Botrytis.
In 2014, they tested two types of sulphur dioxide-generating pads during storage of Coronation grapes. The sulphur dioxide is released from the pads, which are placed on top of the grapes inside the master container when the fruit is packed. This controls the mould and delays stem browning when the pads are exposed to humidity.
In the study, grapes were stored with either a single release pad that released a low concentration of sulphur dioxide slowly over time, a dual release pad that emitted a high concentration for approximately the first 24 hours and then a slow release which can last up to 150 days, or no pad at all.
“We found the dual release pad to work the best, and that Coronation grapes could be stored successfully for up to five weeks postharvest, which is more than double the current storage life,” says Cathline. “Grapes that were stored without either type of pad were completely unmarketable after three weeks in storage.”
With the right concentration and best use of sulphur dioxide, Ontario fresh grape growers could potentially extend their market season right to Christmas, Cathline believes. Cooling grapes as quickly as possible after harvest, ensuring containers are not overfilled, and removing damaged, mouldy or broken berries before the fruit goes into storage will also lengthen storage life.
There are approximately 90 fresh grape growers in Ontario producing about 2,000 tons of fresh table grapes annually with an average gross value of $4 million.
Funding for this one year project was provided by the Ontario Fresh Grape Growers’ Marketing Board and the Ontario Farm Innovation Program through Growing Forward 2 (GF2) a federal-provincial-territorial initiative. The Agricultural Adaptation Council assists in the delivery of GF2 in Ontario.