Putting Food By - Janet Greene [7]
0–1000 ft/0–305 m = 10 psig for 20 minutes
1001–9000 + ft/305–2743 + m = 15 psig for 20 minutes
Summarizing: Ways to Deal with Altitude
Because water boils at lower temperatures the higher we go above sea level—and therefore is less effective as a destroyer of micro-organisms with every increase in altitude—we should:
1. Remember that gas (steam) expands more at higher altitudes, so we allow extra room for it inside our canning jars. This is called headroom, and it’s shown in General Steps in Canning, in Chapter 6. If we did not increase headroom, the contents of the jars would erupt out between the lid and the sealing rim. Bad business.
2. The virtues and drawbacks of dial gauges compared with deadweight /weighted gauges are matters for later discussion. But unless you’d bet your life on the accuracy of your dial—and maybe you are, at that—it’s safer and easier to go along with the 5–10–15 psig of the deadweight gauge at high altitudes.
Other Bothers with Altitude
Jelly-making and cooking syrups for candy and cake frosting are affected by lowered boiling points as you go higher. What happens is that water in the juice/syrup evaporates faster as the altitude increases. So if you are counting on the jelly stage being reached at 8 F/4.4 C above the boiling point of water at sea level—or a reading of 220 F/104.4 C—you’d have some mighty stiff jelly. To deal with this, Dr. Pat Kendall of Colorado State University Extension (Fort Collins) says to lower the final cooking temperature by around 2 F/ 1.1 C for each 1000 ft/305 m in elevation. In short, in Fahrenheit, then, the temperature would be 218 at 2000 feet, 216 at 3000, 214 at 4000, and so on.
Maybe the Sheet Test (Chapter 18, “Jellies, Jams, and Other Sweet Things”) is your best bet.
Just plain boiling food to cook it will take longer—and the pot might be in danger of going dry: again, the problems are lower boiling points plus greater evaporation. These factors also must be considered in cooking by steaming.
Blanching before freezing or drying. Hard to make an across-the-board recommendation here, because so much depends on the food (certainly all vegetables) being treated—age, tenderness, cut size. Leaf vegetables are usually better boiled than steamed, because they tend to mat in the steam basket, but can roll around if popped into water at a thrashing boil and quickly fished out with a skimmer. Dr. Kendall offers a good rule of thumb for the “Centennial State,” where average altitude is 4000 ft/1219 m above sea level. She says that dwellers at 5000 ft/1524 m should preheat vegetables for one minute longer than the sea-level-zone requirement—and should not increase blanching time further at greater altitude.
Baking: yeast-bread doughs rise very quickly, thus allowing less time for flavor to develop; Dr. Kendall suggests letting yeast-leavened mixtures rise twice. Alternatively, you can use half as much yeast as the recipe calls for. The gases from baking powder also expand more, as does the trapped air in beaten egg whites.
Roasting at high altitudes can result in an expensive chunk of meat’s being dry outside and woefully underdone inside. It is essential to test the meat with a thermometer, preferably instant-read.
Deep-frying: temperature of the fat must be reduced the higher you go, she says. Above 3000 ft/914 m, temperature of the fat could be lowered 3 F/1.7 C for each added 1000 ft/305 m as a way to avoid outsides too dark and insides not fully cooked.
Using a double boiler can be tricky because water boils at so much lower a temperature that many starchy thickeners are not activated to do their job. Better, Pat Kendall says, to use a fine-quality, heavy-bottomed saucepan over well-managed direct heat, and Dr. Kendall should know. A long-time member of the faculty of Colorado State CES, she is an expert in canning at high altitudes.
METRIC CONVERSIONS
In her crisp, commonsense fashion, Canada has brought off “going metric,”