The most important condition for preparing yogurt in a double boiler: the milk must be warm and fresh. You need to stir the starter in it and pour it into small jars so that they fit in a double boiler. Some steamers have special cups for yogurt. The starter must be natural, and it must indicate what yoghurt cultures are used. You can buy sourdough at a pharmacy or large supermarkets. The shelf life of yogurt prepared in a double boiler is 5 days at +2C – +6C. Yogurt should be stored in a closed container.