There are cooks who believe freezing extra garlic before the cloves start sprouting is okay, stating that one should coat whole cloves or pureed, peeled cloves in a neutral-flavored oil before freezing. However, the National Center for Home Food Preservation warns against this, as garlic tends to get too strong and bitter once it’s frozen.
There are also certain spices that you should avoid tossing into the freezer. Onion and paprika can have an altered flavor, celery seasoning will get stronger, and curry can develop a musty off-flavor, per the National Center for Home Food Preservation. Similar to garlic, green pepper, cloves, and imitation vanilla can become strong and bitter when frozen.