Method for preparing a leaven using raw milk, in which: - a raw milk is chosen which has undergone no physical or thermal treatment of elimination or of destruction of microbiological germs; - said raw milk is chosen from the group consisting of raw milks whose pH, in a step, named the selection step, of stabilising fermentation by acidifying lactic fermentation of the raw milk at at least one temperature, named the selection temperature, comprised between 20°C to 42°C is capable of reaching: ∘ a value of 5.5 in more than 15 hours, and ∘ a minimum value of 5.0 in less than 48 hours, and then, - a raw milk stabilisation treatment is carried out; ∘ said treatment comprising at least two steps, named the stabilising fermentation steps, succeeding the acidifying lactic fermentation of a fermentation medium, which first stabilising fermentation step is carried out using a fermentation medium comprising said raw milk, and; ∘ in which each stabilising fermentation step of said treatment is interrupted when the pH of the fermentation medium reaches a value comprised between 4.6 to 6.0; ∘ in which at least one step, named a subsequent stabilising fermentation step, is carried out after the first stabilising fermentation step, using a fermentation medium formed of a quantity of a liquid culture medium and a quantity of a fermentation medium, named the preceding fermentation medium, obtained at the end of a preceding stabilising fermentation step, in a ratio by volume of the quantity of preceding fermentation medium to the quantity of fermentation medium comprised between 0.5% to 25%, ∘ each stabilising fermentation step is carried out at a predetermined temperature comprised between 18°C and 35°C, and ∘ each stabilising fermentation step is interrupted by cooling the fermentation medium to a temperature below +4°C. - a raw milk is chosen which has undergone no physical or thermal treatment of elimination or of destruction of microbiological germs; - said raw milk is chosen from the group consisting of raw milks whose pH, in a step, named the selection step, of stabilising fermentation by acidifying lactic fermentation of the raw milk at at least one temperature, named the selection temperature, comprised between 20°C to 42°C is capable of reaching: ∘ a value of 5.5 in more than 15 hours, and ∘ a minimum value of 5.0 in less than 48 hours, and then, ∘ a value of 5.5 in more than 15 hours, and ∘ a minimum value of 5.0 in less than 48 hours, and then, - a raw milk stabilisation treatment is carried out; ∘ said treatment comprising at least two steps, named the stabilising fermentation steps, succeeding the acidifying lactic fermentation of a fermentation medium, which first stabilising fermentation step is carried out using a fermentation medium comprising said raw milk, and; ∘ in which each stabilising fermentation step of said treatment is interrupted when the pH of the fermentation medium reaches a value comprised between 4.6 to 6.0; ∘ in which at least one step, named a subsequent stabilising fermentation step, is carried out after the first stabilising fermentation step, using a fermentation medium formed of a quantity of a liquid culture medium and a quantity of a fermentation medium, named the preceding fermentation medium, obtained at the end of a preceding stabilising fermentation step, in a ratio by volume of the quantity of preceding fermentation medium to the quantity of fermentation medium comprised between 0.5% to 25%, ∘ each stabilising fermentation step is carried out at a predetermined temperature comprised between 18°C and 35°C, and ∘ each stabilising fermentation step is interrupted by cooling the fermentation medium to a temperature below +4°C. ∘ said treatment comprising at least two steps, named the stabilising fermentation steps, succeeding the acidifying lactic fermentation of a fermentation medium, which first stabilising fermentation step is carried out using a fermentation medium comprising said raw milk, and; ∘ in which each stabilising fermentation step of said treatment is interrupted when the pH of the fermentation medium reaches a value comprised between 4.6 to 6.0; ∘ in which at least one step, named a subsequent stabilising fermentation step, is carried out after the first stabilising fermentation step, using a fermentation medium formed of a quantity of a liquid culture medium and a quantity of a fermentation medium, named the preceding fermentation medium, obtained at the end of a preceding stabilising fermentation step, in a ratio by volume of the quantity of preceding fermentation medium to the quantity of fermentation medium comprised between 0.5% to 25%, ∘ each stabilising fermentation step is carried out at a predetermined temperature comprised between 18°C and 35°C, and ∘ each stabilising fermentation step is interrupted by cooling the fermentation medium to a temperature below +4°C.