Wednesday, October 1, 2014

Keep food and drink cool with water


You can keep food and drinks cool on a camping trip or in an emergency without ice or a refrigerator, using the powerful cooling ability of water, which evaporates at 41 degrees, and therefore can cool stuff to 41 degrees, regardless of air temperature, as long as relative humidity is not 100%.
Take a jug of water.  Put it in a shallow pan.  Cover it with a towel, and let the ends of the towel lie in the pan.  Pour water over the towel and fill the pan.  The water evaporates from the towel, which wicks more water from the pan, cooling the towel and the mass of water beneath it eventually to 41 degrees F, the point below which water stops evaporating.   Theoretically, one could cool a box of food by setting it in a bigger box and covering it with a wet towel that lies in water in the larger box.  I cool and keep grapes and melon slices fresh, moist and free of flies by covering their bowl with a wet towel set in a shallow pan of water.
One might think that standing water would likewise cool off to 41 degrees, because it evaporates.  But it has a smooth surface with surface tension, allowing relatively little evaporation compared to a towel, which has a rough surface with lots of surface area to evaporate from, and no surface tension.  Towels are made to suck up and evaporate water efficiently. 
Standing or flowing water also sucks up heat from the mass that it is sitting in or flowing over and holds it in its mass, so a low-running creek or river or standing water can get warm, because it does not evaporate faster than it soaks up heat. 
The water cycle that makes summer thunderstorms depends on evaporation and condensation.  We used to water most of our in-town properties and most of our farmland back in the '80s with sprinklers, and we had frequent wet storms in midsummer, more frequent and stronger uphill and upstream in Jackson  and Klamath Counties, keeping our creeks running. 
In the ‘90s many cities started raising water prices to save water, regardless of local supply or costs.  Drip irrigation and letting lawns dry came into fashion.  Watering plants with drip saves water at the price of losing the evaporative cooling effect of wet plants and soil, and thereby reducing the water cycle that makes summer rain.  Letting land go dry stops most transpiration from plants, and makes no rain.  Half or more of our town and farms are dry.
Now we get more dry storms and forest fires, and creeks going dry that used to run year-round. We have lost nearly a tenth of an inch of midsummer rainfall per decade for the last two decades.  Our July and August storms used to be larger than those in June or September.

September issue, published in GardenGrantsPass.blogspot.com, sold at the Mail Center, 305 NE 6th Street
Gardening is easy if you do it naturally.  Water is not precious; it overpriced.