By Jenny McCoy—Chef Instructor, School of Pastry & Baking Arts
As the summer nears its end, tables at the greenmarket abound with gorgeous fruits and veggies—produce that will be sadly missed in just a few months time. Yet in the modern kitchen, an age-old cooking technique exists to keep enjoying those summery ingredients during chillier months—preservation.
For ages, humans have applied a variety of methods to preserve food, through drying, curing, fermentation, pickling and salting. But in 18th century France, Nicolas Appert, a maverick chef, began researching how to preserve foods in a new way, one that would maintain foods closer to their original fresh state. Initially, he believed that removing the presence of air from stored foods would help them last longer. Though a lesser amount of air can aid the preservation process, he wasn’t quite right. Inspired by a contest organized by Napoleon as a means for feeding the military, Appert continued his food preservation experimentation. Eventually, he found a heating process that could allow foods to remain unspoiled for long lengths of time. A decade and a half of his research resulted in a method we still use today: glass jars filled with foods, then corked and sealed with wax. The jars are then boiled until hot enough to kill microbes that cause food to rapidly spoil, pasteurizing their contents. Appert is credited with the “how-to” of this technique; yet it was later that we learned why it works (thanks, Louis Pasteur). Today we have incredibly easy-to-use canning jars which have screw-top lids and rubber rings in place of cork and wax, which create a vacuum when heated, resulting in a hermetic seal (thank you, John Landis Mason).
Coming back to the present day, I recently paid a visit to Grand Army Plaza, home of Brooklyn’s largest farmers’ market, and loaded up my son’s little red wagon. Courtesy of the enormous assortment grown by Phillips Farms, I did a one-stop-shop and rolled away with flats of blackberries and blueberries, more than a stone of white nectarines, pluots and Jersey peaches, Kirby cucumbers, serrano chiles and jalapeños, and enough varieties of tomatoes to warrant a separate blog post. My neighbor and I shared the bounty and eight hours of canning commenced. We deviated from the classics and made nectarine-coriander mostarda, blueberry-thyme jam and tomato-peach salsa. But we also honored tradition and made good old peach preserves with a hint of lemon and vanilla bean, garlic and dill spears, blackberry jelly, bread and butter slices, and a pack of pickled peppers. After all the gallons of water boiled and dozens of jars filled, the following recipe stood out from the rest, plus: I’ve included a set of simple steps on how to properly can using the water bath method.
Recipe: Blueberry-Thyme Jam
Yield: About 4 cups
2 pints blueberries
2 cups granulated sugar
½ cup water
Zest of 1 lemon, finely grated
8 to 12 sprigs of fresh thyme
¼ teaspoon salt
Pectin, as needed
- In a medium saucepan, cook the blueberries, sugar, water, lemon zest and thyme until mixture is simmering and berries are broken down.
- Continue cooking, stirring frequently, for about 10 minutes, until the mixture thickens to a jam-like consistency. (For faster cooking, mix 1 teaspoon of pectin with 1 teaspoon of sugar and slowly sprinkle over blueberries while stirring constantly. Allow the mixture to boil for a minute to activate the pectin.)
- To test the jam for doneness, drop a small spoonful on a cold plate. If the jam develops a skin once cooled, it is thick enough. If it is too thin, continue to either reduce the jam or add more pectin and sugar until desired thickness is achieved. Can the mixture while it’s hot or let cool to room temperature and store in the refrigerator until you’re ready to can (using the below steps).
How to Hot Water Bath Can:
- Sterilize your canning jars prior to filling. You can do this by placing them in boiling water for one minute (without the lids on!), or by running them through the dishwasher. Wash the lids in hot soapy water. Allow the jars and lids to air dry (do not towel dry as this will negate your sterilization efforts).
- Fill your jars with hot, warm or room temperature foods (you can also can cold foods, but they take longer to pasteurize so I don’t recommend it). I suggest filling the jars with really hot foods to speed up the canning process. Also, a canning funnel will make life a lot easier. Gently tap the jars on a hard surface to remove air bubbles.
- Be sure to wipe any spills or drips on the edge of the jars with a clean paper towel, as they must be clean and dry before closing. Do not use a kitchen towel or your fingers, as this will introduce bacteria into your sterilized jars. When you screw on the lids, secure them tightly—but not as tight as possible.
- Set a metal rack on the bottom of a large pot. (The pot must be at least two inches taller than your canning jars.) If you don’t have a rack, fashion a ½- to 1-inch thick pad made of scrunched up aluminum foil. This helps the jars from being set directly on the bottom of the pot, which causes them to rattle around as they boil.
- Fill the pot with water to a couple inches from the top and bring to a rolling boil.
- Using tongs, carefully place each jar into the boiling water, allowing at least an inch of space around each jar and making sure that there is at least one inch of water above the tops of the jars. You may need to remove some water if your pot threatens to overflow. Cover the pot.
- Once the water has returned to a full, rolling boil, set a timer.
- For jars filled with hot foods, boil the jars for at least 30 seconds for every ounce. For example, an 8-ounce jar will boil for 4 minutes.
- For jars filled with room temperature foods, boil the jars for 1 minute for every ounce. For example, an 8-ounce jar will boil for 8 minutes.
- Once the timer goes off, carefully remove the jars with tongs and set them on a towel-lined countertop. Let them stand at room temperature until completely cool, up to several hours. Do not touch the lids until they are completely cooled, as you may inadvertently seal them by hand. If you hear snapping sounds, don’t worry—that is the vacuum sealing doing its job. Once the jars are at room temperature, any of the jars that did not seal properly can be stored in the refrigerator and eaten immediately. Otherwise, the rest of the canned goods can be stored in the pantry until the seasons change and you crave deliciously sweet raspberries in the dead of winter.
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