# Glass having huge thermal mass when stirring drinks

In the book "Liquid Intellegence: The Art and Sience of the Perfect Cocktail", David Arnold says this:

My question is how the glass affects the chilling? What does he mean by the glass being a "thermal mass"? Can someone explain in more detail? Glass is basicually a thermal insulator, so does the temperature of the glass "warm up" the drink? Why is metal better when it is good at absorbing heat?

(Is this an accurate representation/ sketch of the situation?)

Also: a related question. If you have a chilled drink in a metal cup (not pre chilled) and a glass (not pre chilled), which one stays cooler longer? Which is colder after only 10 - 20 seconds? What I think is that the metal cup will initially be cooler, but that it will also warm up quicker (when all the ice has melted). Or are they just the same initially?

What I think is that metal is good at leading the heat from the environment (heat reservoar) into the metal container, thus making ice melt. When ice melts, it increases absorbs heat, thus cooling the drink. Is this right? What I think is that the cooling is more than the heat gained by the thermal conductivity of the metal, thus the net effect is more cooling.

Any help is appreciated.

• What they are talking about is the amount of heat lost in cooling the glass (or metal container) from room temperature to 0 C. This heat is supplied by the ice in the glass, and thus results in part of the ice melting just to cool down its container. The amount of heat involved is equal to the mass of the container times its heat capacity times the temperature change (20 C). Commented Apr 28 at 13:27
• @ChetMiller so a metal container results in less dilution and faster cooling? Commented Apr 28 at 13:57
• Indeed it does. That is correct. Commented Apr 28 at 13:59

What does he mean by the glass being a "thermal mass"?

They are referring to the heat capacity of the glass container being greater than the heat capacity of the stainless steel container. This is due to the combination of a low specific heat and low mass of the typically thin stainless steel container compared to that of the glass container.

If both containers start out at say, room temperature, before being filled with the ice/liquid mix, the temperature of the stainless steel container will more quickly drop to the temperature of the cocktail mix ceasing heat transfer from the mix to the container, keeping the mix cooler (more "chilled") than with the glass container. Pre-chilling the glass container prevents this from happening.

Hope this helps.

"Large thermal mass" is a common but somewhat sloppy way of desribing a property of glass.

Mass is inertia, or the ability of an object to resist acceleration when a force is applied. A force produces a small acceleration when applied to a large mass.

By extension, "thermal mass" is the ability to resist changes in temperature when heat is applied.

Lead has a surprising amount of mass for its size. Likewise, glass has a surprising thermal mass for its size. It takes more heat than you might expect to raise or lower the temperature of a glass object.

Note that a glass vessel tends to have a larger mass than a metal one. This also makes the thermal mass of a glass vessel larger than of a metal one.

A cocktail will stay close to $$0^o$$ C as long as there is ice in it. If you add heat to the cocktail, it will warm up. This will melt some ice, cooling the cocktail back to $$0^o$$ C.

If you pour a cocktail and ice into a warm vessel, heat will from into the cocktail. The vessel will cool and ice will melt. Minimizing the amount of heat is desirable. One way to do this is to prechill the vessel. Another way is the choose a vessel with a low thermal mass.

You are right to consider the environment. It is generally warmer than $$0^o$$ C, so heat flows into the vessel. A prechilled vessel with a large thermal mass will stay cold longer than one with a low thermal mass.

Metal is a better electrical and thermal conductor than glass. Warm air will heat metal, and the heat will quickly travel through the metal to the cocktail. This is slower for glass.

Radiation is a second mechanism that transfers heat. Hot objects glow in the visible spectrum. Room temperature object glow in the infrared.

Metal reflects light, including infrared light. Glass is transparent. So radiation will warm a cocktail in a glass container more quickly than a metal container. At room temperature and indoor lighting conditions, this is usually not the dominant mechanism. Though things do heat up in sunlight.