The Accidental Scientist: Science of Cooking Exploratorium
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The Crunch Factor
Salt can help your pickles in yet another way.


When you put vegetables in salty brine, the water inside the vegetables flows out into the brine, making the pickles crunchier. This passage of water, known as osmosis, occurs because of the tendency of substances to move through a membrane—like a cucumber skin—from an area of high concentration to an area of low concentration. In this case, the salty brine solution has a lower water concentration than the water inside fresh vegetables, so water will flow out of the vegetables.
The Race of Microorganisms


All foods are continually assaulted by many kinds of microorganisms, racing to eat as much as possible. When you pickle vegetables by fermentation, you help one type of microbe win this "race."

More specifically, you create special conditions in your pickle crock that keep away "bad" spoilage-causing microorganisms, and that allow a unique class of "good" bacteria, called lactic acid bacteria, to colonize your cucumbers.

Why are lactic acid bacteria good?

As lactic acid bacteria grow in your pickle crock, they digest sugars in the cucumbers and produce lactic acid. Not only does this acid give the pickles their characteristic sour tang, it controls the spread of spoilage microbes. Also, by gobbling up the sugars, lactic acid bacteria remove a potential food source for bad bacteria.

Salt gives the good guys an edge.

Adding salt to your pickling brine is one important way to help lactic acid bacteria win the microbial race. At a certain salt concentration, lactic acid bacteria grow more quickly than other microbes, and have a competitive advantage. Below this "right" concentration, bad bacteria may survive and spread more easily, possibly out-competing lactic acid bacteria and spoiling your pickles.

Too much salt is also a problem: Lactic acid bacteria cannot thrive, leaving your vegetables unpickled. What’s more, salt-tolerant yeasts can spread more quickly. By consuming lactic acid, yeasts make the pickles less acidic—and more hospitable to spoilage microbes.

Oxygen gives the bad guys one leg up.

During fermentation, it’s important to keep your crock covered to seal out the air. That’s because oxygen encourages the spread of spoilage microbes. Any exposed pickle or brine becomes a breeding ground for the bad microbes, which can spread to spoil the entire batch.

Too hot . . . too cold . . . just right.

A pickle-maker can also control the microbial garden in a pickle crock by adjusting the temperature. The ideal temperature range for lactic acid bacteria—and successful fermentation—is 70° F–75° F. If it’s too chilly or too toasty in the room, other microbes may gain a competitive advantage over lactic acid bacteria.

Additionally, temperature influences the speed of fermentation: The lower the temperature, the slower the pickles will ferment. By slowing fermentation, you can gain more control over the process.

 

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