There has been a lot of discussion on this subject but unfortunateley like
many things of practical interest to farmers it has too many variables for
the researcher and it is left to farmers to work out for themselves.

Our experience last year may be of some value in determining a
method of resolving the question.

1. We started picking by hand on about 12th November. A few days
later the tramontana blew and it stated to snow. We took the olives to the
frantoio and waited for better weather. This was our "first picked" oil.

2. About a week later we had a demonstration of mechanical picking
put on by our local comune. The variety was Leccino. The pre-harvest test
showed the attachment strenght was too great and so it proved to be as the
shaker only achieved 70% removal. The professor from Perugia conducting the
field day estimate another 7 to 10 days to reach an acceptable 85%

3. After the field day the weather improved and we completed our
harvest by hand. This was the "second pick" and was completed well before
the time the shaker could be used at 85% efficiency.

4. The first picked oil was much better than the second. Of course
both were extravergine but the flavour was much better. We put the same
price on them but almost all the first pick was sold before we sold any
second pick.

5. Hand picking is say 95% efficient. The first cost for mechanical
picking (in this zone as the attachment force is higher on average due to
the large number of green olives at harvest) is the 10% lower yield. (95%
less 85%) The second cost is the lower quality due to late picking.

How much? Difficult to say but Leccino was probably not a good
variety give it is early maturing.

There is plenty of research material on harvesting X time for
various levels of efficiency. There is research on time of harvest and
polyphenol levels. Some one needs to put the two together.

Cheers Brian Chatterton.

P.S I am going to sign off this list in a couple of days as the level of
traffic is so high that I'm afraid my mailbox will be blocked while I'm
away on holiday.
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Brian's message above confirms what I said about quality with hand picking. To get a very tasty (and long conservable oil)
you have to pick early. The ideal point should be the moment when about half of
the olives has changed color from green to violet. Some olives will already be
dark, many will be green with violet sprinkles.
If you pick later, olives start do dry out and get dammaged by insects and
diseases. This is partly due to the olive fly whose larves will devellope,
especially if the climate is mild. If you do not use pesticides, quality
deteriorates the more the longer you wait, but even with pesticides the normal
maturation will cause a progressive loss in quality as soon as the ideal moment
is passed.
On the other hand you can evaluate the loss of efficency in mecanical picking
(even less than 85+ACU- when done earlier) vs. the difference in cost. This will
be mainly a question of the dimension of the orchard. In younger and especially
smaller orchards (+ADwAPQ- 1000) mecanical harvesting will probably not be
cost-efficient (This depends of course also on other factors as the availability
of harvesters for rent and the distance to other orchards). As the ideal time
window for harvesting is quite narrow (not more than 2-3 weeks, as Brian's
experience shows) in big orchards mecanical harvesting might be a must to pick
all the olives within the window, aside the discussion of availability of
manpower. In this case it might be economically resonable to accept a
harvesting-efficiency of 70-80+ACU- and less, one must calculate precisely one
cost against the other. Another question would be if it is ecologically
reasonable, as the olive fly will grow and be reproduced in the remaining
olives, if they are attacked.
Volker