Why water is freeze from top and ghee from button?

We all know that the density of water is 1gm/cm3. During the decrease of temperature of water, the density of the water continue to increase. When the temperature water reaches to 4 degree Celsius, the density became highest. Whereas on further decreases in the temperature of water below 4 degree Celsius, the density of water start to decreases.This phenomena is called the anomalous expansion of water. At 0 degree Celsius( i.e ice), the density of water become the lowest 0.9 gm/cm3. When the cold water comes with the touch of cool air and due to its low density.  it gets frozen instantly. Therefore, the ice floats on the top layer of a water and water seems to be freezes from top to the bottom. 

In case of Ghee, during the lowering of the temperature , those freezes Ghee(solid) will settle down due to its high density than that of liquid Ghee. Hence, the Ghee seems to be freezes from bottom to the top.