Aspects of the production of viscous capsular material by the yoghurt starter, streptococcus thermophilus

20 strains of streptococcus thermophilus were collected. 4 of the isolates were identified as capable of producing a "ropy" capsular material. Instability of "ropiness" during subculture and prolonged storage was described for all 4. Analysis of the plasmid profiles revealed only one contained plasmid DNA, that was shown not to be linked to production of "ropiness". Some technological considerations for the use of ropy variants of streptococcus thermophilus in yoghurt starter cultures were made.