There are two types of plain yogurt:
- Stirred style yogurt
- Set style yogurt - The above description is essentially the manufacturing procedures for stirred style. In set style, the yogurt is packaged immediately after inoculation with the starter and is incubated in the packages.
Other yogurt products include:
- Sweetened stirred style yogurt with fruit preparation
- Fruit-on-the-bottom set style: - fruit mixture is layered at the bottom followed by inoculated yogurt, incubation occurs in the sealed cups
- Soft-serve and Hard Pack frozen yogurt (see Frozen desserts section)
- Probiotic yogourts: it has become quite common to add probiotic bacterial strains to yogourt (those with proven health-promoting benefits, in addition to ST and LB. These could include Lactobacillus acidophilus, Lactobacilus casei, or Bifidobacterium spp. When probiotics are added, it has also become common to add ingredients known as prebiotics, such as inulin, which will, after digestion, aid in the growth of the probiotics in the colon. Inulin, for example, is a polymer of fructose (fructo-oligosaccharide) that is indigestible in the small intestine because we do not have sufficient enzymes to cleave the fructose bonds. However, in the colon, bacterial enzymes can easily release free fructose, which has been shown to positively affect the growth of the probiotic organisms.
Drinking yogurt is essentially stirred yogurt that has a sufficiently low total solids content to achieve a liquid or pourable consistency and which has undergone homogenization to further reduce the viscosity. Fat and solids-not-fat can both be standardized. If the desired snf level in the product is lower than it is in whole milk or skimmed milk, then dilution with water of fruit juices may be used, depending on the requirements of the legal jurisdiction. Sweeteners, flavouring and colouring are invariably added. Heat treatment may be applied to extend the storage life, although this would reduce or eliminate the viable yogourt culture organisms. HTST pasteurization with aseptic processing will give a shelf life of several weeks at 2-4°C, while UHT processes with aseptic packaging will give a shelf life of several weeks at room temperature.