What is the correct ratio of strawberry jam to plain yogurt to make strawberry yogurt?
6 oz Mehadrin yogurts:
PLAIN has 14 g sugar
STRAWBERRY has 31 g sugar
So the strawberry jam adds 17 g sugar to the 6 oz container
Lieber's Strawberry Preserves has 11 g sugar per Tablespoon, so 17 g sugar would be about 1.5 Tablespoons.
This is not quite accurate, because to make room for the jam, Mehadrin had to remove some of the yogurt from the container. The plain yogurt container has 10 g protein, while the strawberry has 8 g protein, all of which comes from the milk (yogurt), so the 6 oz container of strawberry yogurt actually has only 80% of the yogurt of the plain container, or about 4.8 oz.
So the proportion would be about 1.5 T jam to 4.8 oz yogurt, but I would start with a little less, then add if necessary.
ETA: That would be leveled-off Tablespoon, so 1.5 T might be about one heaping T.