Waxes in Extra Virgin Olive Oil

It took forever to settle under gravity, and after it solidified following a cold night, it refused to completely ‘melt’ into its natural fluid state after being warmed. My guess was that involved waxes.

Olive oil mill in Messinia
Sep. 9, 2010
By Richard Gawel
Olive oil mill in Messinia

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Some time ago a friend of mine sent me a sam­ple of an extra vir­gin olive oil, made from the vari­ety Manzanillo and grown in the warm cli­mate of South Eastern Queensland, Australia. The oil was caus­ing her real grief. It took for­ever to set­tle under grav­ity, and after it solid­i­fied fol­low­ing a cold night, it refused to com­pletely melt’ into its nat­ural fluid state after being warmed. On face value, there wasn’t any­thing extra­or­di­nary about this oil. Sure, the sat­u­rated fat con­tent of the oil was on the high side – not unex­pected as hot cli­mate oils gen­er­ally have lower lev­els of monoun­sat­u­rated fat, and nature has to replace it with some­thing! Since sat­u­rated fats tend to be solid at fridge tem­per­a­ture, this might explain why the oil partly solid­i­fied. But they usu­ally melt again when warmed.

Since then I’ve been called upon to ghost­bust a few more of these mys­te­ri­ous EVOO’s. They had a cou­ple of things in com­mon though. They were all Manzanillo’s or dom­i­nant Manzanillo blends, and they were all from warm to hot cli­mates. I didn’t have a solu­tion, but I did have a sus­pect, but until recently the evi­dence was lack­ing. My guess was that involved waxes.

The sur­faces of a lot of fruits includ­ing olives are cov­ered in a thin layer of nat­u­rally pro­duced wax. The wax prob­a­bly acts as a form of bio-armour against attack by plant pathogens like fungi and yeasts, and also pro­vides a valu­able bar­rier against mois­ture loss. The olive plant is well adapted to semi-arid con­di­tions. It’s not sur­pris­ing there­fore that the sur­face of the olive has a coat­ing of wax to keep in that valu­able mois­ture when things start to heat up. When olives are processed into oil, the oil that is released dis­solves the skin waxes and it ends up in the oil.

Recently, Rod Mailer and his group (Mailer et al. 2010) pub­lished some data on the wax con­tent of dif­fer­ent vari­eties grown in hot (SE Queensland), warm (Central Victoria), cool (SW Western Australia) and cold (Tasmanian) cli­mates of Australia (my cat­e­gori­sa­tion of hot-cold, not theirs).

production-waxes-in-extra-virgin-olive-oil-olive-oil-times-extra-virgin-olive-oil-wax-content-by-climate.

Figure 1: Effect of climate on wax content of extra virgin olive oil

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production-waxes-in-extra-virgin-olive-oil-olive-oil-times-average-wax-content-of-extra-virgin-olive-oil-by-variety

Figure 2: Average wax content of extra virgin olive oil by variety

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Ah-hah…. Hot cli­mates pro­duce on aver­age 3x more waxes than cold cli­mates (Figure 1), and of the vari­eties stud­ied, Manzanillo is num­ber 3 on the list of high wax pro­duc­ers (Figure 2) behind Arbequina and Barnea.

While the amount of wax in an olive oil is pretty small (about 1/8th of a gram per litre), their pres­ence prob­a­bly act as a seed for other things to solid­ify.

While the role of waxes in dif­fi­cult set­tling and cold solid­i­fi­ca­tion hasn’t been proven, it is prob­a­bly a con­tribut­ing fac­tor. While there is really noth­ing a pro­ducer can do about it, for some, it is worth know­ing why.

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Reference

Mailer, R.J., Ayton, J. and Graham K. (2010) The Influence of grow­ing region, cul­ti­var and har­vest tim­ing on the diver­sity of Australian olive oil, J. Am. Oil Chem. Soc. 87:877 – 884.

Richard Gawel’s blog is Slick Extra Virgin. Reproduced with per­mis­sion.

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