If the water is allowed to boil away to the point where part of the can is exposed to air, it will explode

Entirely new dishes were also created. In Argentina, dulce de leche, a thick dark caramel sauce made of sweetened condensed milk, became a national dish. There are numerous ways of cooking down condensed milk, but the popular technique is just to put the can in a pot of boiling water and leave it there for four to five hours. Simple, but there is a catch. If the water is allowed to boil away to the point where part of the can is exposed to air, it will explode. 

M. Kurlansky, Milk: a 10,000 year history (2018), 193

Between the mid-sixteenth and mid-seventeenth centuries, the value of a Dutch cow quadrupled

Between the mid-sixteenth and mid-seventeenth centuries, the value of a Dutch cow quadrupled. The Dutch were starting to understand what best to feed cattle, as well as how best to cultivate pastureland. This led to an enormous increase in milk production in Friesland, Flanders, and Holland in the sixteenth and seventeenth centuries. The Dutch cows were producing more than twice the yield of cows in neighbouring countries, and milk was more plentiful in the Netherlands than in most of Europe.

M. Kurlansky, Milk: a 10,000 year history (2018), 96