There are several approaches we can use to do this, often in combination. Pickling, for instance, is about creating a high-acid solution—too high for microbes, but still tasty for us (View Highlight)
Pressure canning, meanwhile, is about raising temperatures to a point so high that nothing will survive. Sure, we could expose our strawberry harvest to the extreme heat of a pressure canner, but to what end? The 240°F (116°C) temperature would kill any and all microbes, but it’d also turn the strawberries into a jar of overcooked mush. It’d be like launching a nuclear bomb when a BB gun would have done the job. Freezing foods is on the opposite end of the temperature spectrum, as extreme cold prevents microbial growth. If you have the freezer space, that’s certainly an option for keeping an abundance of ripe strawberries (View Highlight)
the important thing to keep in mind is that every food contains water (View Highlight)
Since all organisms need water to live, we can prevent them from contaminating our food by reducing the amount of water that’s available to them—that is, by reducing the food’s water activity. (View Highlight)
There are many potential ones, but two of the most powerful are salt and sugar. Add either (or both) of them to the food and they’ll bond with the water molecules, tying them up and making them unavailable to any microbes that come around looking for a nice place to stay. Add enough salt and sugar, and there won’t be sufficient water molecules available for the microbes to survive, even though the food still contains plenty of water (View Highlight)
In our above example, we tossed fresh strawberries with sugar, then cooked the two together. One might assume that we made jam during that process, but we didn’t. While definitions can vary, most would agree that for jam to be jam, it can’t just be cooked fruit in a sugar syrup. It requires a thickener called pectin, a natural fiber in fruits and vegetables that keeps the outer peel or skin firm and intact (View Highlight)
Some fruits, like apples and oranges, have more pectin; some, like strawberries and raspberries, have less. Strawberries, which have very little pectin, will never set into a thick jam on their own—at best, they’ll cook to a thickened syrup. Old European methods of jam-making resolve low pectin levels in a berry jam by tossing an apple, quince, or orange into the mix. Some old recipes don’t even say to do this, as it was just assumed that a home cook would know as much (View Highlight)
Today, we can add either homemade pectin (super-thick apple jelly, for instance) or commercial pectin to our strawberry/sugar mixture to account for its absence in low-pectin fruits like strawberries. Commercial pectin is derived from citrus peels and refined into a powder, and it comes in a couple of different forms. A “regular” pectin is chemically designed to thicken when combined with heat and sugar. A “low-sugar” pectin undergoes additional refinement to work with lower amounts of sugar. Low-sugar pectins also increase the overall acidity of a jam, which erects yet another barrier to microbial growth. They usually contain a small amount of dextrose, which is a hyper-absorptive sugar, and sodium citrate, an acidifier. Using it requires a catalyst, in the form of an acid (from lemon juice) or calcium water. Regular pectin requires no additional catalyst. (View Highlight)
Using the four cups of berries as the base measurement, make your substitutions accordingly—say, three cups of strawberries plus one cup of ginger beer. Or two cups of strawberries and two cups of wine. It won’t affect the result if your substitutions are liquid or solid (View Highlight)