[Le Aeronautical]

Hi all,

Lately I have been making chocolate.  I'm big into making foods, especially from scratch as much as possible.  My question is what makes a liquid a liquid?

In chocolate making you start with a bean maybe 1/2 to 1 inch in length and after roasting and removing the shell you grind it down to particle sizes about 20-30 microns in diameter.  Apparently people can only feel about 50 microns so to us it feels like any other liquid.  The final result is chocolate liquor which can be poured and stays "melted" at room temperature.  Then you add other materials and do more processing to get what you'd buy in the store. 

(this paragraph is slightly off topic, just an fyi) Through processing you remove virtually all water from the chocolate.  Even milk chocolate uses dry milk instead of liquid milk because water causes chocolate to seize up making it impossible to finish processing.  Water actually "wets" the dry but liquidy chocolate.  One example I read that you can compare this to is a potato chip.  They are greasy (liquid) but have no water.  If you put the chip in water it becomes soggy and the complete opposite of what you want.  In chocolate making if you add water to the dry chocolate liquor it becomes pasty and no longer easy to pour.

So my question is what properties makes a liquid by definition a liquid?  Technically if you pulled out a single 30 micron piece from the chocolate liquor it would be a solid.  So Wouldn't my chocolate liquor technically be a powder and not a liquid?  Or is it a liquid when the particle sizes get to a certain size and have certain flow properties?  Got any examples?

Feel free to use advanced terms, I'm mostly through my engineering degree and can hopefully figure it out

-James

[Borek]

I think liquid definition tells that liquid takes a shape of the vessel it is kept in (but keeps constant volume), while solid retains its shape and volume without a vessel. But there is a catch - speed at which the liquid moves depends on its viscosity. Technically tar is a liquid, even if its viscosity makes it behave as solid in our (human) typical time frame.

http://en.wikipedia.org/wiki/Pitch_drop_experiment

Technically chocolate seems to be a suspension.

[Le Aeronautical]

I think liquid definition tells that liquid takes a shape of the vessel it is kept in (but keeps constant volume), while solid retains its shape without a vessel. But there is a catch - speed at which the liquid moves depends on its viscosity. Technically tar is a liquid, even if its viscosity makes it behave as solid in our (human) typical time frame.

http://en.wikipedia.org/wiki/Pitch_drop_experiment

That's true, my problem with that is the volume of the material that you're testing.  If you have a large volume of material and a large container it obviously conforms like a liquid.  But if it's a tiny amount, like one single piece of chocolate at 30 micron diameter, then it's solid and doesn't conform to the container.

Is the liquid property dependent on the amount of it?  There must be some ratio of volume material to particle size and viscosity.

[CrazyCh3m]

That's true, my problem with that is the volume of the material that you're testing.  If you have a large volume of material and a large container it obviously conforms like a liquid.  But if it's a tiny amount, like one single piece of chocolate at 30 micron diameter, then it's solid and doesn't conform to the container.

If you mean a single piece of 30 micron in a fuse chocolate solution it will be a colloidal solution so it's a liquid.
However if you think in an atomic dimension nothing is a liquid even the water's atoms are solid.

[Stepan]

I think for chocolate, the term "liquid" or "solid" should be employed to characterize the property which are important to you at this moment. In reality this is blend of solids (cellulose, sugar, and other), liquid oils, solid oils, water and whatever was introduced there. On macro level, it is viscous liquid; on micro level it is composite muty- phase material

Majority of common "solid" materials have this "dual" nature: butter, ground meat, wax, polymers, asphalt, clay, soil, milk, you name it.