confiture de framboise vs. confiture a framboises

Question

I thought the principal ingredient in a food uses a (my keyboard lacks an accent) rather than de.

Maarten Kamp · Accepted Answer

Carl, 
the attached lesson covers this. 
In a compound noun as in this context, ‘ à’ would indicate a purpose, while de indicates what the item is made of. As the jam is made of raspberries, ‘ de ‘ is appropriate. 
A few other nuances are covered in the lesson as well. 
If you look at the 2nd link you will see ‘ Confiture de Framboises ‘ advertised as packaged in a ‘ pot en verre ‘.
https://progress.lawlessfrench.com/revision/grammar/compound-nouns-are-formed-using-prepositions-a-de-en  
https://www.bringo.ma/fr_MA/stores/carrefour-supermarket/confitures-5/products/confiture-de-framboises-carrefour-370g-1/23099?srsltid=AfmBOooOYxXbh1Nsj5GKUgBjU5oId-3fJ4Ee3wUB_IHnGgB2WOXRLWtO