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Making Sense of Olive Oil Testing

Sep. 25, 2010
Liliana Scarafia

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On July 15th 2010, the UC Davis Olive Oil Chemistry Laboratory in col­lab­o­ra­tion with the Australian Oils Research Laboratory pub­lished a study of extra vir­gin olive oils (EVOO) sold in retail stores in California. Many peo­ple were sur­prised to learn that 69% of imported oils and 10% of California oils ana­lyzed in the study failed to meet the extra vir­gin grade. Quite a few olive oil mer­chants became anx­ious about their olive oil inventories.

Our lab­o­ra­tory ana­lyzes domes­tic and imported olive oil sam­ples to deter­mine oil grade. We rou­tinely per­form the stan­dard International Olive Council’s (IOC) chem­i­cal grad­ing tests (free acid­ity, per­ox­ides and UV absorp­tion) used in the UC Davis study. Our expe­ri­ence allows us to see the ana­lyt­i­cal pro­file of quite a few olive oils, from the very fresh to pretty old.

We received inquiries from mer­chants con­cerned about ensur­ing qual­ity for their cus­tomers and man­ag­ing the risk of mis­la­beled olive oil. Our goal in this paper is to pro­vide a prac­ti­cal per­spec­tive, drawn from the study results, that may be use­ful for retail­ers and buy­ers inter­ested in min­i­miz­ing their risk at an afford­able cost.

First, an overview of the avail­abil­ity and costs of the tests per­formed in the Davis study:

  • Sensory test by an IOC-cer­ti­fied tast­ing panel is not avail­able in the US. Starting in October, the USDA lab­o­ra­tory in Blakely, GA will pro­vide USDA Organoleptic tests. Cost is expected be about $300 per sample.
  • USDA Quality Criteria’s ana­lyt­i­cal tests to deter­mine grade (free acid­ity, per­ox­ides and UV) cost less than $100 per sam­ple, and are avail­able at a dozen US laboratories.
  • USDA Purity Criteria (authen­tic­ity or gen­uine­ness) tests to detect adul­ter­ation with refined oil or non-olive oils may cost up to $2,000 per sam­ple. These are avail­able from a cou­ple of US lab­o­ra­to­ries, includ­ing USDA’s.
  • German/Australian tests (DAGs and PPP) are pro­vided by the Australian Oils Research lab­o­ra­tory. Note that these tests are cur­rently not part of the USDA standard.

Summarizing the study results: 52 oils were tested, only 5 brands from California; 30 were found defec­tive by sen­sory eval­u­a­tion; 11 of those 30 oils also failed USDA/IOC chem­i­cal tests. The German DAGs test failed 23 of those 30 oils and the PPP test failed 15 of them. For clar­ity, grad­ing works like this: if a sin­gle cri­te­rion of the sen­sory or chem­i­cal cri­te­ria is not met, the oil will fail to meet the stated grade and would be assigned a lower one.

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The UC Davis report pro­vides evi­dence as to:

The sen­so­r­ial panel pro­vided a very strin­gent detec­tion of non-extra vir­gin oil

Oils that passed all chem­i­cal tests (IOC/USDA stan­dards, plus DAGs and PPP) failed to meet the EVOO stan­dards by an IOC-rec­og­nized tast­ing panel. Trained tasters can find defects that go unde­tected by chem­i­cal means, such as musty’, or ran­cid­ity’ in old oils .

German/Australian method appear more strin­gent than cur­rent standards

Though nei­ther endorsed by IOC nor adopted by USDA, the German DAGs test appear to be very adept at dis­crim­i­nat­ing vir­gin grade among the oils tested. Let’s stay tuned to its adop­tion in the US.

Among USDA/IOC qual­ity tests, UV Absorption was the most discriminatory

UV absorp­tion at 232 nanome­ters (K232) was the most dis­crim­i­na­tory (10 out of 30) of non-extra vir­gin oils in this study. UV absorp­tion is an inex­pen­sive test that is most infor­ma­tive and cost effec­tive to eval­u­ate older oils, espe­cially when age, stor­age or prove­nance is in question.

Among USDA/IOC qual­ity tests, most oils passed Free Fatty Acids(FFA) and Peroxide Value (PV)

FFA and PV are essen­tial to eval­u­ate fresh oils because those show­ing high val­ues will dete­ri­o­rate more quickly in stor­age. But for oils of unknown age and ori­gin, these val­ues are dicer, and refin­ing can also remove high acid­ity and peroxides.

Going beyond the study: if you decide to have olive oils tested, how could you choose what tests to select? What should you test for?

  • Standard qual­ity tests are a good start. They pro­vide a snap­shot of oil qual­ity at any stage. There is a chrono­log­i­cal pro­gres­sion of dete­ri­o­ra­tion hap­pen­ing in oil from the time of har­vest till a bot­tle reaches the retail shelf and then the con­sumer. Free Fatty Acids result­ing from enzy­matic break­down of oils are a good indi­ca­tor of early oil dete­ri­o­ra­tion. Peroxides are early signs of oxi­da­tion: PV will rise and then taper down while oil is in stor­age. Free acid­ity and per­ox­ides are not dis­cernible by human senses, but both are a pre­lude to ran­cid­ity, which a sen­so­r­ial test will detect later on in old oil. In older oils UV Absorbance val­ues will rise with sec­ondary oxi­da­tion, becom­ing the best test target.
  • Buyers should set their own accept­able cut-off val­ues for PV, FFA and UV absorbance. If empir­i­cally and sci­en­tif­i­cally it is known that oil with a lower FFA and PV at milling will have a bet­ter shelf life, then when sourc­ing new olive oils, buy­ers could set their own FFA thresh­old down to 0.5% or lower, PV well below 20, and K232 sig­nif­i­cantly lower than 2.5. Values approach­ing the IOC/USDA thresh­olds, as sev­eral oils in this study, are indica­tive of lower quality.
  • Consider per­form­ing sen­sory tests. Even if a tast­ing panel is not avail­able (or afford­able), there are quite a few indus­try experts who can taste for a fee, train a buyer’s staff to rec­og­nize obvi­ous defects, and advise on the best char­ac­ter­is­tics of any oil. Their advice may not be meant to cer­tify” the oil, but to empha­size care and qual­ity offered to consumers.
  • Choose ana­lyt­i­cal tests to fit the pur­pose. If you have rea­son to be con­cerned about pos­si­ble adul­ter­ation, then your choices are to test for a com­pre­hen­sive set of tests from the Purity Criteria sec­tion of the USDA stan­dards, or to pur­sue the German/Australian tests. The for­mer are meant to detect blend­ing with refined, and with non-olive oils, while the lat­ter reflect an ongo­ing effort to detect sophis­ti­cated low-tem­per­a­ture refin­ing meth­ods of adul­ter­ation. Which one is more likely, based on your oil source?
  • Demand both the har­vest date and bot­tling date. Since olive oil is per­ish­able and has, at most, a 24 month lifes­pan, har­vest date is essen­tial. But so is bot­tling date because oil may sit in tanks for a long while before bottling.
  • Analytical tests are pass-fail, but dete­ri­o­ra­tion is grad­ual. Next time you read an olive oil lab­o­ra­tory report or bot­tle label, keep in mind that val­ues approach­ing the IOC/USDA thresh­olds are indica­tive of lower qual­ity. The FDA advises against the list­ing of a sin­gle test on the oil label. Rightly so, it may be mis­lead­ing since eval­u­at­ing extra-vir­gin oil requires sev­eral para­me­ters and those val­ues change with time.

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