Empty neck

[Trapper2]

I fill mine full to about a quarter inch from the top with 190° syrup, when it cools it will drop about 1".

I get a premium for my syrup so I want them to look full. Your giving yours away so it may not matter to you.

I always wondered if more air space would invite spoilage/ contamination.

[Haynes Forest Products]

That area is under vacuum and cant cause spoilage because its a sanitary as the rest of the contents. I fill mine to the very top and screw the cap on. I want syrup ion the neck as high as possible because it looks nice.

[Russell Lampron]

I do the same and when it cools the syrup level does drop about 3/4 to 1 inch depending on the size of the bottle.