A New Approach to Preserving Olives

Very few olives can be eaten straight off the tree because of the presence of the bitter phenolic  glucoside oleuropein in the flesh.  This has to be degraded to produce edible fruit.  Traditional approaches have been to use salt or lye (sodium hydroxide) solutions.  This has the disadvantage of possibly adding significant levels of sodium to the diet in a culture where most people are already consuming much more than required and recommended by the Australian National Medical Research Council, the Heart Foundation and other similar bodies worldwide.  Consumers can attempt to rinse out this sodium before use, or another alternative is to use the slower de-bittering technique of repeatedly soaking and rinsing in water.

The present technique avoids these issues by achieving the de-bittering solely through heat application, with partial drying of the fruit until the bitter flavour is no longer present.  The larger the fruit the better the return in terms of edible flesh compared to the pip.  This consideration is less important when the intent is solely to produce oil.  There is usually a successive decrease in bitterness as fruit progress from mature green to turning colour to fully ripe black, so it's the latter that are preferred as they're easier and quicker to process.  The goal in total drying time is first of all to ensure the bitterness is removed by periodic sample tasting.  Thereafter, fruit can be dried to the texture level preferred, ie chewy, flexible or with more drying time, crisp and breakable.  Most people prefer to stop well before the crisp stage, but at these earlier times there will be correspondingly more moisture in the flesh and this reduces storage life.  So you can decide on a 'sweet spot' that  balances your palate preference with how long you'd like to keep a batch before mould growth will develop.  Obviously, they should be stored in an air-tight container to slow this down, but for even longer storage they can be vacuum sealed or stored in vinegar.

1.  After picking, wash the fruit and remove any non-fruit material such as twigs and leaves.

2.  Olive fruits have a thick waxy cuticle on the skin that helps minimize the chances of desiccation while developing on the tree.  Fruit can be dried with this layer intact, but the rate of loss of moisture in the drying process will be far slower.  If the cuticle is cut or compromised by 30 seconds of blanching, the drying proceeds much faster.  Unless you have a special pitting machine, there is no need to remove the pit as typically a home-grower might collect buckets full of fruit at harvest and pitting one by one with the simple hand-operated devices available would take forever.  Similarly, cutting individual fruits one at a time with a knife is very slow.  What speeds up the task with this approach is use of a common kitchen vegetable chopper.  Normal use of these is to place pieces of veges under the rim and then by pushing down a plunger connected to a zig-zag series of cutters you can manually chop up the material very quickly.  Same approach with olives – put several at a time under the rim, a couple of pushes and presto, you have cuts randomly made throughout the fruits.  Several kilos of fruit can be cut in half an hour or so. By severing the flesh you finish up with a more appealing product that hasn't been universally flattened, such as occurs if you just squash the fruit using (say) the bottom of an empty bottle. You obtain even less obvious fruit disruption with blanching.

3.   The treated fruit are then spread out, single-layered, on the tray of a dehydrator and heated at 50°C for sufficient time to enable the de-bittering.  Unfortunately, many dryers available at the retail level don't allow precise temperature control - there might be just 1-3 levels.  If you have one of these types you'll have to experiment to find the best setting; many of them run at above 50°C.  Better and larger cross-flow types with dial-up temperature control are available cheaply on the Internet.  The drying time can be quite variable and depends on the olive cultivar, growing conditions, the stage of maturity when harvested etc.  You should taste a sample after, say, 10 hours to see if bitterness has gone, and if necessary, maybe every six hours or so thereafter until done.  Further heating after this is then focussed on moisture, palatability and storage life.   Total time can be anywhere from 10-35 hours, but that's all there is to it - very fast, so in less than a day or two you have your product and they're certainly tasty and healthy.  You can consume them as is or after adding spices and herbs to achieve your preferred flavours. 

4.  You can store dried fruit for longer under olive oil but this is adding to a product that has already had its own oil content enhanced through drying, and adds further to total calories.  Storing in brine goes back to the original concern of sodium, sodium everywhere in Western diets. 

Barry Madsen