Soy yogurt is made using soy milk, adding yogurt bacteria (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus), sometimes adding sweeteners such as fructose, glucose, or sugar.
It is suitable for vegans, ovo-vegetarians, for people with PKU or other dangerous diseases, and for those with lactose intolerance or milk allergy, as the bacteria for shop-bought soy yogurt are usually not grown on a dairy base. Due to certain recurring doubts and controversies about the bacterial cultures used, most soy yogurt manufacturers nowadays include certified labels, usually by the Vegan Society or similar vegan organisations, clearly visible on the outer packaging.
Soy yogurt can be prepared at home using the same method as dairy yogurt, using soy milk and a starter culture. One tablespoon of sugar per 1 liter of unsweetened soy milk may be added to promote bacterial fermentation. Soy milk on its own lacks the lactose (milk sugar) that is the basic food for the yogurt bacteria.
Soy yogurt may have a slight beany soy taste when made directly from freshly prepared soy milk, but this is less pronounced in shop-bought soy yogurt and in soy yogurt made from commercial soy milk.
Soy yogurt contains less fat than yogurt made with whole milk. This amounts to about 2.7% (the same percentage as soy milk), versus 3.5% in dairy yogurt. However, dairy yogurt can be made with 2%, 1%, or fat-free milk, and soy yogurt can also be made from reduced-fat soy milk.
In 1998, the cost of soy yogurt was similar to dairy yogurt.
Plant-based milks have different structures and components than dairy milk. Though they can be used to make many products similar to those made from dairy, there are differences in taste and texture. For example, “soy, almond, [and] coconut yogurts do not have the same delicate and smooth structure that conventional yogurts have.” Since plant-based milks do not contain lactose (the food of Streptococcus thermophilus and Lactobacillus bulgaricus), plant-based yogurts usually contain different bacterial strains than a dairy yogurt, such as Lactobacillus casei, Lactobacillus rhamnosus, and Bifidobacterium bifidum. Plant-based yogurts also vary considerably in their nutrition and ingredients, and may contain gums, stabilizers, high-intensity sweeteners, and artificial colors.