Adding Water During Olive Oil Production Lowers Quality, Researchers Find

New research pub­lished in Food Chemistry has con­firmed that adding water dur­ing the olive oil extrac­tion process can pro­foundly affect extra vir­gin olive oil qual­ity.

A team of Portuguese sci­en­tists eval­u­ated what hap­pens when water is added to the olive oil pro­duc­tion process using Arbequina olives, one of the most widely grown olive tree cul­ti­vars in the Iberian penin­sula.

They found sig­nif­i­cant dif­fer­ences in the water-added extra vir­gin olive oil com­pared to the same batch of olives processed with no water addi­tion. The olives trans­formed with­out adding water had higher lev­els of polyphe­nols in the result­ing oil and were far more resilient to oxi­da­tion.

The researchers ana­lyzed the chem­i­cal and sen­sory pro­file of Arbequina olive oil extrac­tion in sev­eral set­tings: from no water added dur­ing the pro­duc­tion process to a max­i­mum of 6.2 per­cent of water added for every kilo­gram of processed olives.

In all cases, with or with­out water, the result­ing olive oils were clas­si­fied as extra vir­gin olive oil, accord­ing to the International Olive Council stan­dard.

“Despite the extra vir­gin olive oil clas­si­fi­ca­tion, com­pared with the water incor­po­ra­tion… extrac­tion with­out water addi­tion resulted in [olive] oils that showed less pri­mary oxi­da­tion (lower per­ox­ide val­ues and K232), greater total phe­no­lic con­tent (+12 to 22 per­cent) and higher oxida­tive sta­bil­ity (+22 to 31 per­cent),” the researchers wrote.

Additionally, olive oil pro­duced with­out added water had a 5 to 13-per­cent higher sec­oiri­doid con­tent, mainly com­pris­ing olea­cein, a pow­er­ful antiox­i­dant.

As a result, olives trans­formed with­out any added water pro­duced an oil with a more intense ripe fruity sen­sa­tion.

The researchers con­cluded that olive oil pro­duc­tion with­out adding water results in higher-qual­ity Arbequina extra vir­gin olive oil with higher polyphe­nol counts.

“The qual­ity and the sta­bil­ity of the Arbequina oils can be favored if extracted with­out adding water dur­ing the olives indus­trial milling,” they wrote. Doing this also means greater resilience to pro­longed stor­age and han­dling.

Water addi­tion has been used for gen­er­a­tions by many millers as it was often con­sid­ered an effi­cient method to get more oil out of the paste. However, this belief has been chal­lenged over the years.

For exam­ple, a study con­ducted nearly a decade ago by sci­en­tists at the University of Extremadura in Spain showed that adding water to the process caused a decrease in oil yield and oil extractabil­ity for both of the cul­ti­vars that had been tested.

Such stud­ies sug­gest the need for millers who still add water to exam­ine the ben­e­fits of water-less extrac­tion, which might also result in reduced energy con­sump­tion, less liq­uid residue and a higher qual­ity olive oil.

• Food Chemistry