Preheat the oven to 100ºC.
Wash the jar and lid in hot soapy water.
Sterlise the jar in the oven for a minimum of 30 minutes. Place the lid in the oven with the jar five minutes before the sterlisation is due to complete.
Once the bottle and lid are sterlised, leave to cool.
Wash and pat dry the greengages, discard any that are discoloured or split open.
Remove the stem completely.
Break down the rock sugar into smaller pieces if it is too chunky.
Once the bottle is cooled down, add a layer of the plums in the bottom and then a layer of sugar. Make sure the plums are tight, be careful not to bruise them though.
Repeat this process till until all the plums and sugar are used up. You should have reached about ¾ of the capacity of the jar.
Check that the top layer of plums is secure and nicely packed and the plums will not float.
Pour over the Vodka, completely submerging the greengages. Leave at least an inch or two above the top layer of plums. The plums will release their juice and you don't want it to overflow!
Close the lid on the jar and place the jar in a cool, dry, dark place.
Give the Jar a shake once in a while to help the sugar assimalate with the alcohol.
After 4 months, you can have a taste. At this point you can remove the greengages or leave them.
If you do decide to remove the greengage, use a sterlised spoon, or one that has been washed in hot soapy water. Transfer the umeshu into bottles. Store the bottles in cool, dark and dry place for two months.
After two more months it is ready to be consumed. Umeshu mellows with age, so I prefer to leave it for longer. Its best to start drinking it after a year.