Thursday, April 7, 2011

:: kinetics of glass cooling ::

In a post a week and a half ago, I researched the effects of a cocktail glass' initial temperature on the drink that was poured into it. In that study, I shook a "Vodka Martini," strained it into room temperature, ice water-chilled, and freezer-chilled glassware, and measured how this altered the drink temperature. While unchilled glassware provided the warmest (and thus least desirable) drink, the ice water's and freezer's effect lowered the drink temperature by 1.9°F and 4.4°F, respectively, relative to the unchilled glass. While these numbers will vary by drink composition, glass size and thickness, and other variables, the end result was that the coldest drink would come from the coldest glassware. What did 2 or 4 degrees difference mean? It was like waiting 3 or 5 minutes after the drink was poured to first sip it (less time for warmer rooms). If the point of it as described by the Savoy Hotel's Harry Craddock was, " drink a cocktail... quickly, while it's still laughing at you," every moment or degree of chilling wasted was one too many.

In the comments section of that study, Anna of the TwoSheetsInTheWind blog asked about the kinetics of the chilling since I took mine to extremes (glasses were put in the freezer more than 90 minutes in advance and on ice water over 20 minutes in advance). Anna inquired, "When you shorten the time the glass spends in the freezer, how does it compare? At one bar I frequent, they go through a remarkable number of glasses; on a busy night, it is not uncommon to see the dishwasher run, emptied into the freezer, and a glass from that run used within 10 or 15 minutes. What sort of effect does the freezer have versus ice water when you are looking at starting with a hot glass and can only freeze it for 15 minutes?"

When I asked a local bartender about his dish washing machine's cycle, he could not tell me when the sterilization stage fell or how hot glasses were when they came out of the washer. Instead of dealing with glasses at that moment, I started with room temperature glasses as a good starting point.

For me the question was how selecting the right glassware (stored at room temperature) for the recipe I just decided upon would effect either the spontaneity of the process or the end result. Clearly, we cannot fit all or even a significant fraction of our new and vintage glassware in our freezer (unless, of course, we got a much bigger freezer), but how much preparation would it require for ice water and freezer chilling to take its full effect on glassware? Should we be dedicating a portion of the freezer to storing a selection of glassware at all times?
To get up to speed on the other experiments, please read:
• Part 1: Effects of Glass Temperature
• Part 3: Effects of Glass Thickness on Drink Temperature
• 2 Libbey Martini Glasses
• Freezer
• Ice from Tovolo Trays from Freezer
• Cold Water from Sink
• Digital Thermometer with Thermocouple (-58°F to 2372°F, ±0.1°F)
• Timer Application on Droid Phone
• Digital Scale

• Measure room temperature.
• Stick thermocouple in freezer, close door, and record the kinetics of chilling when not attached to a glass by taking temperature values every 30 seconds. Stop when temperature stabilizes to acquire freezer temperature.
• Weigh cocktail glass #1.
• Tape thermocouple inside the glass to lowest part of the cocktail glass' bowl. Wait until temperature equilibrates.
• Place glass in freezer, close door, and record temperature every 30 seconds.
• Weigh cocktail glass #2.
• Tape thermocouple to the outside of the glass to less than an inch up from the bottom of the bowl.
• Add 5 ice cubes and weigh the ice. Quickly add 3 oz cold water and weigh water.
• Record temperature every 30 seconds until temperature stabilizes.

• Different glass sizes and shapes will affect the end result. Here, the 2 glasses are comparable to each other, but not to other glasses.
• Variations in room temperature will affect results.
• Amount of times the freezer door is opened and closed will change the results (will happen in reality, not in this experiment though).
• Amount of air circulation in different freezers may vary and affect chilling rates; also the number of other warm glasses placed in freezer may alter the results.
• My thermometer was never calibrated.
• Experiment was only performed once per condition instead of triplicate like the last experiment.
• The thermocouple could be affected by outside air, instead of reading just the temperature of the glass. No insulation on the airside of the thermocouple was added besides tape. Hence, the glass could seem colder in the freezer and warmer at room temperature.
• Tap water was not pre-chilled with ice.

• Room temperature: 63.6°F
• Freezer temperature: >5.9°F
• Ice water temperature: 33.9°F

• Weight of glass #1 (freezer): 235.8 grams
• Weight of glass #2 (ice water): 239.2 grams
• Weight of ice: 157.3 grams (5 uncracked Tovolo cubes)
• Weight of water: 86.5 grams

• Data are single runs, not averages:

• Time for ice water glass-chilled to reach coldest point: 330-360 seconds
• Temperature of ice water-chilled glass: 38.8°F
• Difference between glass' coldest point and ice water: 4.9°F (effect of air temperature)

• Time for freezer-chilled glass to reach coldest point: over 25 minutes (>1500 seconds)
• Temperature of freezer chilled glass at end of 25 minutes: 12.5°F
• Difference between glass' coldest point and freezer: 6.6°F (effect of air temperature and incomplete cooling)

In terms of spontaneity, ice water chilling was fast. At our room temperature and glass type, the full extent of the chilling occurred in 5-6 minutes. In contrast, the freezer's chilling was slow to reach its fullest effect; in fact, I tired of the experiment after 25 minutes of taking measurements ever 30 seconds. The rate of cooling was decreasing, but it was still several degrees away from its potential (at least 6.6°F, if not more due to air temperature effects on the thermocouple). Perhaps another 10 minutes or so was needed putting the range for completion at 35-45 minutes. As a positive note for spontaneity, after around 7 minutes (disregarding air temperature effects on the thermocouple), the freezer chilled glass was as cold as the ice water chilled one once it reached equilibrium. Therefore, at that time point, both techniques were equivalent in merit.

Again, the choice of glassware will effect the chilling kinetics. Moreover, while a freezer will work on the whole glass, the ice water will only work effectively on the glass' bowl and a temperature gradient will be set up in the stem. Of course, in chilling Old Fashioned glasses, the ice water would work on the whole glass including its thick base. While our Libbey glasses are not the thinnest of our collection (not the thickest either), most glasses we own are thinner which would, therefore, help to accelerate both time courses.

As the previous experiment showed, freezer-chilled glassware was the optimal choice; however, as this experiment shows, that peak of perfection is hard to do on the fly or in a high volume establishment in the weeds. The previous experiment showed that ice water chilled glassware was an intermediate choice; here, the peak of this middle ground technique was reasonably fast (under 6 minutes). At home, this would require a small amount of patience. At a high volume bar, it would require a steady line of glasses chilling in advance. Of course, the solution is to go to bars when they are less busy to have the best chance of getting cold glassware and thus cold drinks.


Anonymous said...

I've been perfectly happy chilling glassware with cracked ice. I give it a stir and let it set for however long it takes to leisurely assemble the rest of the drink, usually maybe 3-7 minutes. I used to keep glassware in the freezer, but I just don't have the room anymore. Awesome post, though - thanks for taking the time.

frederic said...

I first tried the experiment with just ice and the results proved slower since there was less contact with the glass (I did not crack my ice, so the finer the ice particles the better). I scrapped that data and went with ice+water.

And from the first experiment, one take home message is that any chilling will help, even if it's not to completion. So even if you finish making your drink in 3 minutes of chilling time, those minutes will help.

Anonymous said...

Oh, right, I do add water to the ice. Just ice is slow. And I feel that a bit of stirring speeds up the cooling also.

adrinkwithforrest said...

Soda water also accelerates the cooling process..
Great post!

TikiGeeki said...

Awesome article! I'd love to hear your thoughts on an ice article I wrote: Mad Science of Cocktail Ice. Ice is probably the least respected ingredient at a bar. I hope more bars think about it and temperature in general more.

frederic said...

TG - I remember reading that a few months ago. I was impressed at the experiment of how long ice cubes lasted once the drink is cooled (and the measurement of the shrinkage). Cool work... er, I'll leave that unintentional pun there.

Anonymous said...

This is ridiculously cool! What's the thermocouple you used?? I really want one that I can hook up to my computer without spending a ton of money.

frederic said...

If you want to save a lot of money, get the thermometer that I did that came with 2 K-type thermocouples (Model DM6802B) that you can find on eBay for $20-25 or so shipped.

If you want one that will hook up to your computer, it will cost you more. The website uses "a Measurement Computing 8 channel thermocouple input module (Model USB-TC, a pretty good deal at $329)" and a variety of thermocouples. No clue what software they used.

If that's too much, go the pen and paper route. Although their input module will handle multiple temperature readings at once.

Pantagruel said...

Nice work.

You mention that thinner glass will chill more quickly, which is very true but the thinner the glass the less the initial temp of the glass matters because it will have a relatively lower mass so it takes less time and energy for it to warm up.

A thick bottomed DOF will take forever to come down to temp in the freezer, but it will keep its contents much colder much longer. There is no free lunch.

I try to keep a few glasses in the freezer for personal use, but for entertaining that goes out the window pretty quickly.

frederic said...

Good points, Pantagruel. I did notice the extra thermal effects of the glass from the freezer in the kinetics of the first study. While the slopes of the linear parts of the room temperature and ice water-chilled glasses were similar, the freezer-chilled glasses provided a more horizontal slope. Meaning that it slowed the glass from warming up over time (as opposed to the initial 30-60 seconds when the drink equilibrated rapidly).

The DOF might not take forever with ice water, but relatively much longer. I thought about expanding the studies to different glassware, but keeping each step simple was important.

Anonymous said...

Excellent follow-up! Obviously, the solutions for a busy bar are difficult, but for all of us nitpicky home drinkers with limited ice and limited freezer space, you just made our lives a whole lot better!

Pantagruel said...

One more thing, when I want a quick chill I scoop up some ice from the ice maker and then bury the ice filled glass in more ice, so it's sorta a hybrid between sitting in freezer air and contact with ice water.

This gets 'em pretty cold pretty quick.