“With enough butter, anything is good.”
Pictured is a butter bell, a French crock which originated in the 19th century which keeps butter fresh at room temperature and spreadable.
The crock (in the foreground) is packed with a stick of butter and then inverted (Principle 13 – The Other Way Round) into the dish (background) which is partially filled with cold water. Like a diving bell, the air under the butter is trapped and the water prevents new air from getting in and turning the butter rancid. Here’s a video that shows how it works.
Is it a crock?
I hesitate to quibble with a two century design, but if the goal is room temperature butter in the absence of oxygen, then this solution lacks a certain je ne sais quoi. The problem being that the butter is still in contact with air between it and the water. The fact that the air can’t circulate is the benefit of course, but the same result could be achieved with a threaded lid to the butter container without the water dish and inversion.
The goal is not airtight, it’s air absent or at a minimum surrounded in inert gas.
My inspiration is boxed wine. You are free to speculate why. If you are not familiar with the boxed wine, it is an Australian invention from the 1960s wherein an airtight bag with a tap is held in a cardboard box. As wine is drained from the tap, the bag collapses but no air is drawn in. (Principle 7 – Nested Doll, Principle 30 – Flexible Membranes, Thin Films)
The form factor I am considering is a hybrid of that and the toothpaste tube. Imagine a toothpaste tube with the same cap that is used on upside down ketchup bottles – Principle 13 – The Other Way Round. Within the typical toothpaste container is another thin film bag in which whipped butter is contained. Squeeze the outer container and the whipped butter is squeezed out, but no air retreats back in with the butter.
Why whipped butter? It should be more squeezable. Butter whipped with nitrogen is already commonly offered as easier to spread straight out of the fridge. Principle 39 – Inert Atmosphere, Principle 31- Porosity