Why does tomato sauce get stuck in the bottle?

Why does tomato sauce get stuck in the bottle?

Tomato sauce is a highly viscous paste made from tomatoes, spices and various other additives. Hence, the sauce can only move if it is shaken or if sufficient force is applied. Everyone knows from pouring water out of a bottle that the liquid that leaves the bottom of a bottle has to be replaced by air bubbling through the water from the open end of a bottle.

Tomato sauce, is too viscous to allow air bubbles to pass through it easily . This is why a vacuum forms in the bottom of the bottle when the sauce moves away from it. As a result, a pressure difference is created that works against the force of the gravity, which is pulling the sauce downwards.

When tomato sauce stubbornly refuses to leave the bottle there are several ways of getting it out. Plastic bottles of sauce are flexible and can be squeezed to eliminate the vacuum. Sauce in rigid bottles, on the other hand, sometimes with disastrous results. The third method helps  with both types of container - simply insert a drinking straw deep into the bottle so that air can pass through the tomato sauce to the bottom.