When good oils go bad

Defects can occur because of mishandling during and after harvest, and during processing, bottling and storage. They lead to unacceptable aromas and flavours in the oils. Some of the common defects are listed below.

Fusty: This is a defect characteristic of olives that have been stored in piles for too long before processing. The aroma is similar to old or decomposing olives.

Metallic: The flavour found in oils extracted with both new processing plants and/or used for the first time at the beginning of the processing season.

Muddy sediment: The oil may have been left in contact with sediment and water that settles in tanks and vats.

Musty: This is a mouldy flavour, caused by mould growth on olives stored in piles in humid conditions for several days before pressing.

Rancid: Rancidity is a common defect. It is elevated during improper storage or transport, at high temperatures, when stored in sunlight, and once the oil has been opened and exposed to air. Over time, rancidity increases - the oil may have deserved the extra virgin tag when bottled but it hasn't stood the test of time.

Winey: A winey or vinegary flavour mainly due to fermentation from the growth of yeasts during poor storage of the olives.

Olive oils can also be tired or flat. Tired oils taste "old" and not fresh - it's a sign an oil is starting to go rancid. Flat oils have a weak flavour and aroma, often from the loss of fruitiness of the oil. New Zealand olives may suffer frost damage. This can affect the oil. There may be flavour changes from a loss of flavour and aroma.

Report by Belinda Allan.