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Dairy Chemistry – Part IV of IV: Water Properties

Water is the biggest constituent of almost all dairy products (the exceptions are some cheeses, butter and spray dried products such as dry whey and non-fat dry milk). Milk, in fact, is comprised of 87% water. In general, we ignore water when we think of dairy products, but some of its properties and interactions are very important to how dairy products function.  Below is a table listing some of the properties of water.

Some of the more interesting properties of water are as follows:

• Water is unique in that it is the only natural substance that is found in all three physical states—liquid, solid, and gas—at the temperatures normally found on Earth. Earth truly is a water world. 

• Water is unusual in that the solid form, ice, is less dense than the liquid form, which is why ice floats.

• Water is called the "universal solvent" because it dissolves more substances than any other liquid. This means that wherever water goes, either through the ground or through our bodies, it takes along valuable chemicals, minerals, and nutrients.

• The water molecule is highly cohesive—it is very sticky. Water is the most cohesive among the non-metallic liquids.

• Water has a high specific heat index—it absorbs a lot of heat before it begins to get hot. This is why water is valuable to many industries and in your car's radiator as a coolant. The high specific heat index of water also helps regulate the rate at which air changes temperature, which is why the temperature change between seasons is gradual rather than sudden, especially near the oceans.

• Water has a very high surface tension. In other words, water is sticky and elastic, and tends to clump together in drops rather than spread out in a thin film, like rubbing alcohol. Surface tension is responsible for capillary action, which allows water (and its dissolved substances) to move through the roots of plants and through the tiny blood vessels in our bodies.

• Water ice can exhibit up to sixteen different phases (packing geometries) depending on temperature and pressure. Though the clear majority is the one phase (ice 1h) we are familiar with. Below is a phase diagram:

• It is possible to make a glass (non-crystalline solid) form of water, but this takes extremely fast cooling and ultra-cold environments (below -215°F or −137 °C that is the glass transition temperature for pure water). Some say that most of the water in the universe is glass state water. 

• Water like many substances can be supercooled. Water normally freezes at 273.15 K (0 °C or 32 °F), but it can be "supercooled" at standard pressure down to its crystal homogeneous nucleation point (where water spontaneously crystalizes) at almost 224.8 K (−48.3 °C/−55 °F). The process of supercooling requires that water be pure and free of nucleation sites. It is this phenomenon that enables many animals and plants to withstand very cold temperatures without damage from ice crystals forming within their tissues. 

• Likewise, water can superheat. This is the phenomenon where a liquid is heated to a temperature higher than its boiling point, without boiling. Superheating is achieved by heating a homogeneous substance in a clean container, free of nucleation sites, while taking care not to disturb the liquid. We often see this when we heat water in the microwave. Sometimes the very hot water suddenly explodes out of its container on disturbing the water or adding a small number of particles.

I hope this quick review of water and its properties can be beneficial when we think about dairy products as well.