Slush Science

[Holly Moore]

On recent afternoons I have been studying the Slurpee-like lemonade served by my local coffee house La Colombe.

My research concentrates on its melting. As the frozen lemonade melts it produces an intensely rich lemonade. That I understand, or, at least, absorb.

What I find mystifying is what is melting. As it melts, the lemonade color disappears from the ice at the top of the slush. Over time the bulk of the remaining slush turns white. Alas, I lack the patience to compete a day's research, usually discarding the remainder a half hour or so into my experiment.

What I do not understand is why the lemonade seems to be melting out of the slush leaving what appears to be frozen water. Is it the citric acid, the sugar, and/or God's will that influences relative thawiness?

Further, does this process increase the concentration of the lemonade I slurp? I believe La Colombe starts with a two to one water to fresh squeezed lemon ratio. Does this account for the increase in intensity? Is the slurpable solution more one to one, or is it even approaching pure juice and sugar?

Truth be told, I tire of this research. Perhaps someone who actually paid attention in food chemistry class can enlighten me so I can get back to doing the crossword puzzle during my afternoon respites.

Edited June 27, 2008 by Holly Moore (log)

[Dr. Teeth]

Lemme take a shot at it before somebody that really knows the answer comes on. Ice forms in the temperature it does in part because water molecules which are polar (positive charged end and negative charged end) line up so neatly - positive end of one next to negative end of another.

Kind of like how the suitcase looks when my wife packs it.

When you put in forign molecules that are soluble in water, like salt or sugar they disrupt the neat positive to negative end matrix.

Kind of like what happens when I try to pack 2 books and a pair of jeans into the neatly packed suitcase

The ice becomes less stable, the freezing point goes up and it melts faster.

[emilyr]

I've always just kind of assumed that a slush is a suspension. As the syrup/water mix freezes, the water freezes separately from the syrup which has a lower freezing temp (so the "slush factor" comes from water ice and syrup liquid). As the suspension rests, it separates, and the syrup sinks to the bottom.