Cyclopeptide fermentation at increased metal ion concentration

Method for the preparation of a cyclopeptide comprising an amino acid chosen from the list consisting of 3-hydroxyproline, 3-hydroxy-4-methylproline, 4-hydroxyproline and proline which method comprises fermenting a culture of Aspergillus sp., Coleophoma sp. or Glarea sp. in the presence of nutrients comprising calcium ions, copper ions, iron ions, magnesium ions, manganese ions, molybdenum ions and zinc ions, characterized in that the metal ion concentration of said calcium ions is between 0.4 and 1 mg.kg−1 and/or of said copper ions is between 0.15 and 0.5 mg.kg−1 and/or of said iron ions is between 3 and 10 mg.kg−1 and/or of said magnesium ions is between 70 and 200 mg.kg−1 and/or of said manganese ions is between 5 and 15 mg.kg−1 and/or of said molybdenum ions is between 0.15 and 0.5 mg.kg−1 and/or of said zinc ions is between 0.7 and 2 mg.kg−1.