One of the most proud moments of my life was the discovery that we still had ice on Day 21 of a 21-day Grand Canyon trip in August. Call it a small victory, but I’ll take my successes where I can get them. I lived and breathed ice for three weeks before we left, lovingly adding a 1/2 inch of water to each cooler each day and freezing the new additions overnight into beautiful specimens of near airless magnificence. Even so, once we were on the river, ice management became a crap shoot. Every stinkin’ trip the same argument comes up: Do we drain the cooler water or leave it in? There are more passionate arguments about draining water than there are about the politics of the presidential election.
I’ve heard unwavering opinions from all: anecdotes from trips past, actual rocket scientists relaying the laws of physics, quietly confident Grand Canyon guides guaranteeing that there’s a correct process.
To drain or not to drain? That, my dear Shakespeare, is the real question.
For the answer, we turn not to an experienced outdoorsman. We hit up the bad boy of every party: physics.
No student of physics will answer a question without first setting parameters. For our purpose, here are the assumptions: The cooler is relatively efficient at doing its job, ice refills are not readily available, and responsible practices are being enforced by that one cooler cop who is always bellowing about not keeping it open for too long. We’ll also assume that it’s not the dead of winter and the ambient air is warmer than freezing.
The crux of the whole shebang is that we’re assuming the goal is to keep the cooler contents as cold as possible for as long as possible. In other words, we’re assuming you’re more interested in a cold beer than the size of the ice chunk next to it.
A Physics 101 Primer
Hot and cold always seek equilibrium. It’s not just a good idea, it’s the law of physics called thermal equilibrium. Left to their own devices (i.e. without outside influence and with enough time) a hot mass and a cold mass will always seek compromise to meet somewhere in the middle. Thermal equilibrium is achieved by heat transfer, which effectively is just the exchange of thermal energy via BTUs. We can effect the rate of heat transfer in certain situations, but in purely scientific terms, the rate is determined by the temperatures of each mass and characteristics of the medium in between them.
So how does that apply to my cooler?
Thirty-two is the magic number for the cooler conundrum. When ice comes in contact with air or a mass that’s warmer than 32' F, a heat transfer occurs. Ice will work its H2O-based ass off to cool down any non-frozen food or drink in its space. More accurately, a warm beer placed in a cooler of ice will emit heat as it chills. This heat causes the ice to melt into water until the temperatures of the remaining ice, beer, and water reach equilibrium.
Even if you were magically able to pack your cooler perfectly and with all the contents at 32' or colder, an even more critical heat transfer still exists between the air space in the cooler and the outside air temperature. No big surprise that the hotter the day, the more quickly your ice will melt.
So we know that the tipping point from ice to water and vice versa is 32' F, right? It’s also the crux of the drain-or-not-to-drain quandary because melting ice will stay precisely at its melting point (32''F) until the conversion from solid to liquid is complete. In plain English: as long as there is some ice left in the cooler – regardless of how much water is sloshing around – the temperature of the ice/water mixture will hold steady at 32' F.
So the ice is in a race to 32''F and it’s not getting any warmer until it is completely melted. If you drain the water, the ice isn’t going to get any colder. Because the water is already at 32' (and not warmer), draining it won’t slow down the rate at which the ice melts. It would only open up space for warm air to come into the cooler, which would accelerate the rate of melt for the remaining ice.
Result: In order to keep your food and drink as cold as possible for as long as possible, don’t drain the water while any ice still exists in the cooler.
Cooler Best Practices:
If you can, chill the entire cooler before you use it.
Definitely chill your food and beer before putting it in the cooler.
Fill ‘er up. Leave as little air space in the cooler as possible. Some recommend adding some sort of insulation to take up space.
Keep your cooler out of direct sunlight as much as you can. If a shade tree isn’t available, cover your cooler with wet blankets or burlap.
Minimize the number of times you open it and how long you keep it open.