Sweet condensed milk is milk that has been filled out some sugar water evaporation to keep rotten spoiled milk? Based on the principle that sugar will make the osmotic pressure is high. Most bacteria will not be able to grow and expand in syrup with high concentrations.
Sweetened condensed milk is evaporated off some of the sugar to maintain the milk spoiled rotten. Using principles that sugar is made. High osmotic pressure. Most bacteria can not grow. And propagation in syrup with higher concentrations.
Condensed milk is milk evaporates water, some more sugar to treat not bad milk rotten. Based on the principle that the sugar will make a high osmotic pressure, bacteria, most will not be able to thrive.