When boiling meat, add a spoonful of vinegar to the water to make it more tender.
When making a stew or soup that has bones in the meat, add a 1-2 tablespoons of vinegar. This will cause the calcium in the bones to leach out of the bones into the broth. A gelatinous effect will be produced when the batch is cold. There is no taste to this result but the benefits you will realized in the extra calcium in your diet will be welcomed.