The invention relates to a method for growth of bacteria, such as Gram negative bacteria and its corresponding supernatant. The bacteria are cultivated without substantial release of endotoxins from the bacteria into the surrounding medium. Thereby the need of purification steps necessary to remove endotoxins are reduced or eliminated such as when the bacteria are producing a product which later on should be administered to a mammal, such as a human. The bacteria are also cultivated without substantial formation of acetic acid. The level of the carbon/energy source is controled during the cultivation and oxygen limitation is avoided through regulation of the temperature. The method may be used for cultivation of bacterial in fermenters.