There are numerous documented techniques, with varying levels of complexity, for re-activating the yeast in naturally conditioned beer. The method described below may leave some readers, experienced in growing yeast cultures, aghast. "What! No stir plate, no malt, no alcohol swabs, no nutrient, no way!" However, for Coopers yeast, it works.
Method
1. Buy a six pack of Coopers Original Pale Ale and place upright in the fridge for about a week for the yeast to settle.
2. Mix about 600ml of boiling water and 4 tablespoons of dextrose/sugar in a pyrex jug, cover with cling-wrap and leave to cool in the fridge for about 30mins.
4. Open 4 bottles and decant the beer into a jug, leaving behind the yeast sediment - about a couple of centimetres.
5. Pour the sugared water equally into each bottle, cover with cling-wrap and secure with a rubber band.
6. Shake the bottles then place them in a dark spot at a temperature in the mid 70's F.
7. Give the bottles a shake in the morning and at night to keep the yeast in suspension.
8. After around 2 to 3 days the yeast should become active and begin forming a head.
9. Pitch the active yeast into a brew immediately or store in the fridge for about a week. Just remember to pull it out of the fridge to warm for couple of hours prior to pitching.
A few points to keep in mind for successful Coopers yeast reactivation; use beer with the latest "Best After" date, lower alcohol content is better, it's okay to hold the culture at slightly higher temps to promote a quicker reactivation, make sure the culture smells okay before pitching, buy another 6 pack for each culture and don't forget to drink the decanted beer.