Another amazing invention, in my opinion, is refrigeration. We take it for granted but refrigeration, especially mechanical refrigeration, is pretty new.
Ice has been used to cool food for millennia. In 400 BC Persian engineers had already mastered the technique for storing ice. Ice was brought in from the mountains and stored underground in specially designed spaces. The ice was used to chill treats for royalty. (Of course )
In England during the sixteenth to seventeenth centuries in England low lying areas near the Thames were flooded in winter. The ice was stored in an ice house, insulated by sawdust, moss or something similar. As early as 1823 ice was imported from Norway and of course in the US, ice was transported from the North to the South, i.e from Maine to points as far away as South Carolina. This led to a new industry: the ice trade. Ice was cut from frozen ponds and streams and stored in ice houses before being shipped – eventually – around the world. As one would expect, the citizens of New York City and Philadelphia became huge consumers during their long hot summers.
The ice trade revolutionized the U.S meat, vegetable and fruit industries. It led to the invention of ice boxes; yes, wooden boxes lined with zinc or tin and other insulators like moss, sawdust or cork, with a box for ice. A drip pan underneath caught the melted water. The horse drawn wagons of ice and the ice man became a familiar sight. By 1907 81% of the households in New York City had ice boxes and they are widely credited with a drop of 50% of infant mortality in the summer.
Mechanical ice began to be produced in the late 1800s but was chancy and the process used toxic ammonia gas. Mechanical refrigerators did not go to the homes until the various fluorocarbons were developed.
Prior to refrigeration milk spoiled quickly; in fact, all perishable foods spoiled quickly. People had cold cellars to cool food and tried putting milk down the well to cool it. I read that cheese was an attempt to use milk before it soured.
So, to my way of thinking, the refrigerator is even more important than indoor plumbing.