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<pre>Dear All ...

The following thoughts have been extracted from an large article that
appeared in the December 1993 issue of Olivae magazine (IOOC). It dealt
with the Effect of Water Quantity on Olive Oil Quality. I believe that
there is more recent research on this topic as well (Bari reports etc) but
this is all I have on this computer.

The experiment was carried out in Italy where rain is received during the
winter and where the summer is fairly dry. The young olive trees were
planted five years earlier and were growing in a medium textured soil. Every
ten days from June to September (December to March in Australia) the trees
received 36mm of irrigation water.

The irrigated trees set 33% more fruit (by number) than the non-irrigated
ones. The individual fruits were 20% heavier and the total crop weight per
irrigated tree was 41% greater than the non-irrigated trees.

In this trial, the percentage of oil retrieved from both the irrigated and
non-irrigated trees was almost identical. Secondly, both groups of trees
produced high quality extra virgin oils. The acidity levels and peroxide
values were almost identical.

In 1996 we asked Dr Juan Caballero, director of the Olive Research Institute
in Cordoba, Spain, about the difference in oil quality from dryland and
irrigated trees. He stated that, "We have not found any difference in the
quality of olive oil produced from irrigated and non irrigated trees". (If
you're online Juan you may have some more thoughts on this topic.)

Here comes another surprise. The polyphenols were 16% higher in the oil
produced from the fully irrigated trees. These natural antioxidants also
help protect the oil from oxidation during storage and thus help to extend
the shelf life of the product.

In light of recent postings which showed that polyphenols were reduced in
irrigated oils there must be other factors which affect the levels. Maybe
soil types and/or fertiliser schedules have an impact on how irrigation
changes affect the polyphenol levels????

Kind regards,
Julian Archer
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