New Zealand Producer Uses Brix Levels to Determine Ideal Harvest Moment

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.

Ross Vintiner uses Brix readings from his olives to help determine the ideal moment to harvest.
By Lisa Anderson
Jun. 27, 2023 14:56 UTC
Ross Vintiner uses Brix readings from his olives to help determine the ideal moment to harvest.

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.

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.- Ross Vintiner, co-owner, The Vintiner’s Grove

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.

See Also:Genotype Plays Significant Role in Fatty Acid Content of Virgin Olive Oil

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).”

Brix read­ings

Brix read­ings are a mea­sure of the sugar con­tent in a liq­uid, typ­i­cally in the con­text of mea­sur­ing the sweet­ness of fruit juice, wine or other bev­er­ages. The Brix scale is based on the refrac­tive index of the liq­uid, which changes in pro­por­tion to the amount of dis­solved sugar. Brix read­ings are expressed as a per­cent­age, and a higher Brix read­ing indi­cates a higher sugar con­tent. In agri­cul­ture and food pro­duc­tion, Brix read­ings are often used to deter­mine when fruits or veg­eta­bles are ripe enough for har­vest or to mon­i­tor the progress of fer­men­ta­tion in wine or beer-mak­ing.

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 harvesting olives.

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.


Dali Estate prides itself in its biodynamic farming practices.

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.

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