Here's a nice recipe for Syrian Syrian Sweet-and-Sour Olives.

• 1 1/2 cups olives, about 24
• 1 1/2 cups small to medium brine-cured green olives or yellow olives, rinsed,drained,and lightly crushed or scored (about 8 ounces)
• 1/3 cup olive oil
• 1/3 cup hamod er rumman pomegranate concentrate
• 1/3 cup water
• 1 small onion, sliced
• 1 tablespoon brown sugar
• 10 whole black peppercorns
• Combine all the ingredients in a 0.5l jar.

Cover and let stand in the refrigerator for at least 3 days and up to 3 months.

Have fun!

This is a very detailed recipe, but very easy, from:

http://www.rusticgirls.com/food/pickling-olives.html

First of all you need to start with olives that are freshly picked and in good condition. There are three stages in ripeness that you can use for pickling. They are green, ripe green which is a slightly more yellow colour and black which is fully ripe. Black olives are usually not fermented, which is why they have a milder taste than the green ones. Green and ripe green olives produce stronger flavours. For this method, we will use about twenty five pounds (10 kg) of green olives.

A food grade container of around five gallons (20 litres) is used for the pickling process. The olives are traditionally soaked in spring water for several hours to wash them. They are then drained. To prepare the pickling solution you will need about one and a half gallons (7 litres) of spring water at room temperature. Add one and a half pounds (800 grams) of sea salt and about half a pint (300 grams) of vinegar. White wine or cider vinegar is best.

With a sharp knife, make a single deep cut lengthways in each olive to assist the fermentation process then put them in the container with the liquid. Weigh the olives down with a large diameter plate so they are all covered by the liquid. The plate should not fit too tightly in the container so the gasses can escape. It is not critical to exclude oxygen as in the winemaking process, so with this method there is no need to seal the container.

The olives should be fermented at room temperature for up to a month before they can be eaten, but will become more flavoursome and fully mature after three months. They can be tasted any time during fermentation as a way of checking their flavour. The bitter compounds are safe to eat.

The reason for fermenting the olives in this traditional way is to break down the phenolic compounds and the glycoside, oleuropein which are contained in the raw fruit that give them their harsh bitter taste. When these compounds are broken down, lactic acid is produced. This is an excellent natural preservative which will enable the olives to be stored without refrigeration for several months.

Aside from the fiddly, time consuming process of cutting each individual olive, this traditional method of pickling olives is quite straightforward and produces excellent results. The final product can be served with many different herbs and spices, steeped in olive oil or vinegar flavoured with chilli, garlic or lemon juice or stuffed with peppers, cheese or anchovies. By using this traditional and relatively simple method you never need to feel put off pickling your own olives again.

A recipe for pickling olives:

3 kg olives

3 Tbl salt

12 Tbl olie oil

600mls white / cider vinegar

1.25 litres water ( boiled and cooled)

1 clove garlic

1 small red chilli

dried oregano or other herbs

Method:

After picking , wash the olives well. Slit each olive on 2 sides. Place in a large bowl and cover with ordinary tap water. Change the water daily for 10 - 14 days, so the olives will lose their bitterness.

Sterilise some jars (I find 3kg makes about 12 medium jars) . Place olives and garlic, chilli and herbs into jars . Mix the boiled water, vinegar, salt and olive oil in a bowl. Pour into the jars making sure you cover the olives completely. Put on well - fitting lids. That's it. Wait at least 2 weeks before starting to eat. You will find the flavour changes with time - some people prefer them with the ' fresh' taste you get after 2 weeks, others prefer the more mellow flavour after 6 months or more. They should be stored in a cupboard but when you open a jar put it in the fridge if its a big jar / you think you might take ages to finish the jar / if the weather is hot. I always put open jars in the fridge in summer or they go mouldy, but I never do in winter as we eat them pretty fast and I don't use huge jars. Good luck.