The invention concerns the production of aluminium oxide trihydrate crystals by the bayer process by digesting ground bauxite, filtering off the red mud, cooling the filtrate and crystallizing out the dissolved aluminium hydroxide as gibbsite. Before and/or during the crystallization, polyglycerins of the general formula: H-(OCH2CHOH-CH2)n-OH are added, n being a whole number greater than or equal to 3.
