This Canning Bubble Popper/ Measurer 591 is used while canning to remove air bubbles before sealing jars. To make sure that air bubbles have not been trapped inside the jar, run the bubble popper around the edges of the jar, gently shifting the food, so that any trapped air is released. After the air bubbles have been removed, more liquid may need to be added to the jar to ensure proper head space.
Convenient measure marks on one end of the bubble popper for measuring the head space in your jars to avoid overfilling. Allowing the proper head space according to processing directions for specific foods is necessary so that all the extra air will be removed during processing and a tight vacuum seal will be formed.
I have not used this tool; I purchased it as part of a gift package. But it looks excellent & sturdy & I'm sure works exactly as it should. If you know someone who cans/preserves, I'm sure they can use it!