# Water getting hotter once frozen?

I packed a fridge with temperature sensors and took over the temperature control in order to have extra cold beer.

One of those sensors is submerged in the middle of a container containing a 4.5% seltzer so I can get an idea of the temperature inside the surrounding beer cans.

This submerged sensor is the yellow curve at the bottom:

I'm trying to explain what happened around 6:25.

I was maintaining the seltzer at -3°C and I confirmed it was not frozen. However I think I was maintaining it slightly below it's freezing point.

This morning I saw that it somehow raised in temperature abruptly and it's now in this jelly/half frozen state.

I'd like to know why this really sharp raise in temperature. Is this how freezing works?

• When you wrote 4.5% seltzer, what does the 4.5% refer to? Is it the level of carbonation, or something else (e.g., alcohol)? More generally, what are the ingredients of your seltzer? Does it contain only water and CO2, or are their other things in it as well? May 21 at 17:55
• It's 4.5% alcohol/vol. and the rest of the ingredients are carbonated water, sugars (glucose-fructose), Malted barley, Yeast, Natural flavors, Citric acid, Potassium sorbate. May 22 at 19:20

I'm speculating, but it's possible this is what happened:

I looked up the freezing point of seltzer water (aka club soda), and it's $$\pu{-10 ^{\circ}C}$$. Plus your product also contains alcohol and sugars, which would further lower the freezing point. Since you have a temperature sensor in it, I assume it's open. Thus the seltzer will gradually lose its dissolved $$\ce{CO2}$$, and the alcohol will gradually evaporate. As this happens, its freezing point will go up.

I'm guessing that your seltzer lost enough $$\ce{CO2}$$ and alcohol for its freezing point to exceed $$\pu{-3 ^{\circ}C}$$. When that happened, the seltzer, which was at $$\pu{-3 ^{\circ}C}$$, entered a "supercooled" state (meaning it was now a liquid below its freezing point), and thus started to freeze. When a substance freezes, it releases thermal energy (you have to add thermal energy to melt something; freezing is simply going in the opposite direction). That could be what caused the temperature jump.

It sounds like its freezing point is now $$\pu{-1 ^{\circ}C}$$, and the "half-frozen state" you are seeing is phase coexistence between ice and the remaining sugar-water solution.

I don't know why you're seeing the "jelly-like" consistency, but it could be from the dissolved sugars and malted barley left behind in the water as the ice forms.

• I'm guessing sugar is a potential "contaminant." Water could freeze, leaving a liquid phase of concentrated sugar water. May 21 at 1:09
• @LevelRiverSt Seltzer water doesn't contain sugar (it's nothing but water with dissolved CO2 and some mineral), unless some got in there by accident. May 21 at 2:07
• @theorist the OP called it a "4.5% seltzer" so I'm assuming its some kind of seltzer based cocktail-ish drink, not pure seltzer water. May 21 at 5:05
• When a supercooled liquid flash-freezes, it often turns into a very fine slush, which I suppose could seem like jelly in a way. If the slush is stirred aggressively, it returns to a more fluid state with compacted ice settling at the top. May 21 at 9:44
• @mbrig I thought the OP was referring to the level of carbonation. But you're right, it could be something else. E.g., it could be hard seltzer, where the 4.5% is the concentration of alcohol. I will ask the OP! May 21 at 19:54