Unlike with grapes or other fruit, Ross Vintiner harvests olives when the sugar level falls, indicating that oil is accumulating and polyphenol content remains high.
Building on his grape-growing experience, one award winning New Zealand producer is developing a cost-effective method to determine the best moment to harvest his olives to balance high yields with polyphenol content.
Ross Vintiner, co-owner of The Vintiner’s Grove, told Olive Oil Times in April that some New Zealand growers were trying to develop a harvest schedule to optimize the content of polyphenols and other antioxidants in their extra virgin olive oils.
Based in the Wairarapa region on the North Island, Vintiner said the experiment was based on his previous experience, but he soon found research to back it up.
“I discovered later that Spanish research verified my working assumption,” he told Olive Oil Times.
Vintiner said he independently observed that it is best to harvest when the Brix readings of his olives fall, the reverse of what is done across fruit industries. “I harvest when Brix levels fall for each variety, the opposite to [what] a winemaker [would do],” he explained.
“Research shows that unlike grapes where maximum Brix is required to harvest, in olives minimum sugar – Brix levels – equals maximum oil and total polyphenols,” Vintiner said. “This is an inexpensive way of determining my harvest time. A refractometer to measure Brix costs around $100 New Zealand (€57).”
“Around a decade ago, following my experience of grape growing, I was curious: Was there a relationship between olive fruit ripening, oil content and sugar levels in olive fruit?” he recalled.
Vintiner then started measuring the Brix levels of olive leaves and fruit and found that rising readings of the leaf sap indicated rising readings of the olive fruit juice.
“Then Brix levels fell, the opposite of grapes, coinciding with physical signs of oil in the fruit,” he said. “Each cultivar was different.”
“A minimum value for sugar correlates to a maximum value for oil content,” Vintiner explained. “I observed the usual sugar levels and ripeness for each variety, counting maximum ripeness from days after full bloom.”
“These results enabled a predictive harvest index [a measurement of crop yield] for each variety,” he added. More