How does freezing yogurt affect the quality?

Stonyfield Farms claims that you CAN freeze yogurt. After it's thawed, however, don't expect it to be the same consistency as refrigerated yogurt.   Their website tells us, "It will have a different look and texture than fresh yogurt."  A few of the bacterial cultures die off in the freezing process,  but, since there are billions of them in any given serving of yogurt, it's not significant enough to affect the nutritional quality.  The main issue is the consistency and texture of the yogurt itself.
 
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Stonyfield Farms Frequently Asked Questions