To keep the octopus meat tender there are a few little secrets that are worth knowing. The first is to immerse the octopus three times in boiling water and then remove it before you submerge it permanently. The second is to boil the water very gently, in other words barely simmer the water. The third factor is the cooking time: allow just 20 minutes per half kg of octopus. Any more than this and your octopus will become tough!