Yeasts are members of a higher group of microorganisms called fungi . They are single-cell organisms of spherical, elliptical or cylindrical shape. Their size varies greatly but are generally larger than bacterial cells. Yeasts may be divided into two groups according to their method of reproduction:

  1. budding: called Fungi Imperfecti or false yeasts
  2. budding and spore formation: called Ascomycetes or true yeasts

Unlike bacterial spores, yeast form spores as a method of reproduction.