A Streptococcus thermophilus selected from the group consisting of: the DSM 27029 strain, deposited under the Budapest Treaty on March 21, 2013 in the name of Danisco Deutschland GmbH at the Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen, GmbH; the DSM 27030 strain, deposited under the Budapest Treaty on March 21, 2013 in the name of Danisco Deutschland GmbH at the Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen, GmbH; the DSM 27031 strain, deposited under the Budapest Treaty on March 21, 2013 in the name of Danisco Deutschland GmbH at the Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen, GmbH; and a mutant strain of the DSM 27029 strain, of the DSM 27030 strain, or of the DSM 27031 strain, wherein the milk acidification kinetics of said mutant is characterized by: - an average speed of acidification between pH 6.00 and pH 5.30 which is at least 70.10 -4 UpH/min or equals 70.10 -4 UpH/min, calculated as described in Assay I, in particular which is between 70.10 -4 and 250.10 -4, between 70.10 -4 and 200.10 -4, between 70.10 -4 and 180.10 -4, or between 70.10 -4 and 140.10 -4 UpH/min, and - an average speed of acidification between pH 5.30 and pH 5.00 which is less than 22.10 -4 UpH/min or equals 22.10 -4 UpH/min, calculated as described in Assay I, in particular which is between 1.10 -4 and 20.10 -4, between 2.10 -4 and 22.10 -4, or between 2.10 -4 and 20.10 -4 UpH/min wherein assay I consists in: Commercial half-fat UHT cow-milk (fat 1.5 % w/w) ["Le Petit Vendéen"; GLAC - France] is supplemented with 3% (W/W) skimmed milk powder. After dissolution, the mix is heat treated at 90°C for 10 min. The heating step from 20-25°C to 90°C lasts no more than 35 min and the cooling step from 90°C to 35°C-45°C lasts no more than 45 min. Just before inoculation, 1g/ 100 L (w/v) of sodium formiate is added. The inoculation is performed with strains preserved at -80°C in milk based medium. The inoculation rate is 1.10 6 CFU/ml of milk-base. The incubation temperature is set at 43°C +/- 1°C, and kept constant in a water bath during the fermentation. A Cinac system was used for online measurement of pH change. The pH is recorded each 5 min during 24h, and summarized in a table or presented as a CINAC curve. The 3 following parameters are determined: time for pH = 6.00 (T pH6.00), time for pH=5.30 (T pH3,30) and time for pH=5.00 (T pH5.00). These parameters are obtained directly by the online recording, or when the time to obtain the targeted pH is not present in the table, a linear interpolation is done between the two recorded data. the DSM 27029 strain, deposited under the Budapest Treaty on March 21, 2013 in the name of Danisco Deutschland GmbH at the Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen, GmbH; the DSM 27030 strain, deposited under the Budapest Treaty on March 21, 2013 in the name of Danisco Deutschland GmbH at the Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen, GmbH; the DSM 27031 strain, deposited under the Budapest Treaty on March 21, 2013 in the name of Danisco Deutschland GmbH at the Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen, GmbH; and a mutant strain of the DSM 27029 strain, of the DSM 27030 strain, or of the DSM 27031 strain, wherein the milk acidification kinetics of said mutant is characterized by: - an average speed of acidification between pH 6.00 and pH 5.30 which is at least 70.10 -4 UpH/min or equals 70.10 -4 UpH/min, calculated as described in Assay I, in particular which is between 70.10 -4 and 250.10 -4, between 70.10 -4 and 200.10 -4, between 70.10 -4 and 180.10 -4, or between 70.10 -4 and 140.10 -4 UpH/min, and - an average speed of acidification between pH 5.30 and pH 5.00 which is less than 22.10 -4 UpH/min or equals 22.10 -4 UpH/min, calculated as described in Assay I, in particular which is between 1.10 -4 and 20.10 -4, between 2.10 -4 and 22.10 -4, or between 2.10 -4 and 20.10 -4 UpH/min - an average speed of acidification between pH 6.00 and pH 5.30 which is at least 70.10 -4 UpH/min or equals 70.10 -4 UpH/min, calculated as described in Assay I, in particular which is between 70.10 -4 and 250.10 -4, between 70.10 -4 and 200.10 -4, between 70.10 -4 and 180.10 -4, or between 70.10 -4 and 140.10 -4 UpH/min, and - an average speed of acidification between pH 5.30 and pH 5.00 which is less than 22.10 -4 UpH/min or equals 22.10 -4 UpH/min, calculated as described in Assay I, in particular which is between 1.10 -4 and 20.10 -4, between 2.10 -4 and 22.10 -4, or between 2.10 -4 and 20.10 -4 UpH/min