New Zealand Producer Uses Brix Levels to Determine Ideal Harvest Moment

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 he was devel­op­ing a har­vest sched­ule to opti­mize the con­tent of polyphe­nols and other antiox­i­dants in his 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.

Vintiner said he refined his approach by doing fur­ther research. ​“There is no strong cor­re­la­tion between sugar and phe­no­lic com­pounds,” he said. ​“However, total phe­no­lic com­pounds decrease dur­ing ripen­ing.”

“As we har­vest for high polyphe­nols and phe­no­lic com­pounds decline dur­ing ripen­ing, I over­layed typ­i­cal polyphe­nol decline on the har­vest index to esti­mate my har­vest time,” Vintiner added. ​“I checked the index each year against sugar lev­els and polyphe­nol results to ver­ify the model.”

“The index pro­vides a reli­able and accept­able trade-off to be made between har­vest dates, oil con­tent and polyphe­nols,” Vintiner said. ​“By mea­sur­ing Brix lev­els of olive juice and pre­dict­ing oil con­tent, I could bet­ter esti­mate har­vest time to achieve high phe­no­lic com­pounds and a rea­son­able oil yield per cul­ti­var.”

“A har­vest index, unique to each grove, can be con­structed that relates Brix oil con­tent with likely phe­no­lic lev­els,” he added.

Vintiner, who grows Frantoio, Koroneiki, Kalamata, Leccino, Pendolino and Picual trees at his Dali Estate, said he has been using the above model to con­sis­tently achieve high total polyphe­nols (with lev­els exceed­ing 250 mil­ligrams per kilo­gram) for all these, as well as medium to high oil yields (except for his Kalamata table olives).

“Our best polyphe­nol oils are either at or near the top total polyphe­nol oils in New Zealand,” he said. ​“In my view, along with fla­vor, high phe­no­lic olive oils define true qual­ity and healthy olive oil.”

He said olive skin color is not a strong indi­ca­tor of when to start har­vest­ing in New Zealand. ​“Olive flesh color is often used, with white flesh to the pit indi­cat­ing ripeness,” Vintiner said.

“There are also tests for fruit water con­tent to deter­mine ripeness,” he added. ​“Other farm­ers fol­low tried tim­ing and expe­ri­ence. It is likely that real-time olive total polyphe­nols will soon be mea­sured by a hand-held device.”

Vintiner said he runs more tests on all com­po­nents of his groves than most olive grow­ers and tests new ideas to guide informed deci­sions.

Vintiner’s inno­v­a­tive approach to olive grow­ing and extra vir­gin olive oil pro­duc­tion has also led him to develop new fer­til­iz­ing meth­ods. As a result, Dali Estate’s groves have dou­bled their soil organic mat­ter – plant and ani­mal waste at dif­fer­ent stages of decom­po­si­tion – in five years.

Olive pomace is a rec­og­nized fer­til­izer, but Vintiner took a new approach. ​“I have pio­neered new ways of fer­til­iz­ing olives, includ­ing using olive pomace, all within the con­fines of Biogro (New Zealand’s main organic cer­ti­fi­ca­tion agency) organic cer­ti­fi­ca­tion and bio­dy­namic prac­tice,” Vintiner said.

Vintiner worked within these con­fines, as Dali uses only cer­ti­fied organic and bio­dy­namic meth­ods and inputs since Vintiner bought the prop­erty in 2011.

“I use our pomace in a fer­ment that takes about three weeks to mature and lasts up to two years,” he said. ​“Fermented pomace tested high in plant avail­able nitro­gen and potas­sium, essen­tial for growth and fruit fill, respec­tively.”

“I use this diluted fer­ment as a foliar spray in spring and autumn,” Vintiner added. ​“As the fer­ment is low in micro­bial bio­mass – the mass of the liv­ing com­po­nent of soil organic mat­ter, a sig­nif­i­cant mea­sure of soil qual­ity – I add organic effec­tive microor­gan­isms [mixed cul­tures of nat­u­rally-occur­ring organ­isms] at low-per­cent­age appli­ca­tion.”

He said using research and his own expe­ri­ence, he has found that micro-dos­ing, apply­ing fer­til­iz­ers a lit­tle at a time and often, achieves the best results.

He also cre­ates a mix of net­tle, com­frey and lucerne fer­mented with kelp to pro­duce a ground drench high in min­er­als olives most need. In addi­tion, he has fur­ther sup­ported Dali’s soil health by plant­ing clovers, plan­tains and com­frey; together with other plants and trees, where his sheep graze and fer­til­ize the soil.

Vintiner, with his knack for explor­ing uncharted ter­ri­tory, is the only grower of Kalamata olives – which he said are very high in phe­no­lic com­pounds – in the Wairarapa region. ​“Kalamata trees grow well in the Wairarapa but have prob­lems fruit­ing,” he said.

But he found meth­ods to over­come this. ​“Using a vari­ety of tech­niques, includ­ing plant­ing on a sun-fac­ing slope, annual prun­ing and com­pan­ion plant­ing with com­frey, Dali Kalamata fruit each year,” he said.

“I am pas­sion­ate about grow­ing the best soil, soil life and every­thing diverse above it,” Vintiner con­cluded.