Salt is the only rock that humans regularly consume in its raw form. Despite its ubiquitous use today, salt was once used as currency due to its rarity and difficulty in manufacturing. In fact, the word “salary” comes from the Latin word salarium which was a payment of salt given to Roman soldiers. It wasn’t until the invention of industrial processing techniques in the mid-19th century that salt became a staple of everyday culinary life.
Before refrigeration, salt curing was one of the primary forms of preservation for most foods because it keeps microbes and bacteria from forming and adds flavor in the process. Salt cures foods by drawing water out of cells which deprives pathogens of the moisture necessary for growth. As water is removed from the cells, salt takes its place, enhancing the final product's flavor and maintaining an inhospitable environment for harmful bacteria. The salt also weakens muscle fibers, affecting the texture of the cured meat.
Nitrates and Nitrites Along with regular salt (sodium chloride or NaCl), several mineral impurities are used to preserve meats. While salt acts to pull out water and impact flavor, sodium nitrite (NaNO2) and sodium nitrate (NaNO3) are also highly effective at halting bacterial growth and enhancing both the taste and color of cured meat.
Food grade sodium nitrite comes in the form of a pink salt, interchangeably referred to as instacure #1, pink curing salt #1, or prague powder #1. It contains about 6% sodium nitrite and 94% table salt. Sodium nitrate, on the other hand, is comprised of 6% sodium nitrite, 4% sodium nitrate, and 90% table salt and is referred to as pink curing salt #2 or prague powder #2.
The difference between these two salts is critical to understand as salt #1 can be used in fast cures and can be cooked and eaten quickly, while salt #2 must be cured long enough for the nitrates to convert into nitrites (nitrates should never be cooked and consumed). The vibrant reds and pinks inherent in cured meats occur when nitrite encounters oxygen and the resulting nitric oxide binds with the iron present in the meat.
In the Middle Ages, saltpeter, or potassium nitrate (KNO3), was used to cure meat and enhance its flavor and color. Saltpeter, however, does not contain the nitrites necessary to cure meat. Instead, bacteria in the meat transform the nitrates found into saltpeter into the nitrites required for curing and preservation, much like Salt #2. Saltpeter is now only rarely used as it is much more efficient to use nitrites rather than waiting for nitrates to be converted.
While there is some controversy about potential adverse health effects from nitrates and nitrites, they are essential for food safety. Even "uncured" products, such as organic bacon, are cured with the naturally occurring nitrites in celery salt or beet brine. These sodium compounds work to halt the growth of one of the most dangerous pathogens pervasive in cured meats and other preserved foods: clostridium botulinum or botulism. The name itself comes from the Latin botulus for sausage. Botulism is anaerobic, heat resistant, and acid-tolerant—it's also lethal, even in small doses.
Dry Curing—Hanging and Smoking Dry-cured meats are fresh meats that have been coated in a mixture of salt and salt #2, refrigerated, and then rinsed and hung. During dry curing, enzymes in the meat work to break down proteins into flavorful, savory amino acids and peptides such as glutamic acid.
In pork, the breakdown of unsaturated fat can produce the flowery and fruity notes often associated with the famous cured hams of Europe. Hanging salt-cured meat in a temperature- and humidity-controlled environment allows the curing process to occur safely over an extended period, from weeks to months and potentially years.
Smoking meat can be used in conjunction with salt curing and enhances the process by adding compounds within the smoke that slow down fat oxidation, inhibit bacterial growth, and impart flavor. Meat can be either hot-smoked or cold-smoked. During hot smoking, meat is held above the wood, allowing it to cook and smoke simultaneously. Alternatively, cold-smoked meat is placed in an unheated area through which smoke passes. Cold smoking often creates more robust flavors in the meat, especially if the meat is somewhat moist during the process.
Wet Curing—Brining Wet curing involves either soaking meat in a salty brine or injecting that brine straight into the meat itself. Commercial bacon and ham are often injected with brine and tumbled to massage the mixture through the muscle fibers. For home wet-curing, meat should be submerged in the brine and kept below 42 degrees Fahrenheit. During the wet curing process, salt enters and displaces moisture in the meat cells just as it does during dry curing, but the surrounding liquid keeps the meat moist, which allows for more varied cooking options and a juicier product.
Tips for Salt Curing In any curing, starting with a fresh product is essential. Meat curing is essentially controlled decay, and that decay is easier to manage if the meat hasn't already been sitting out for a week. For dry curing, humidity should be around 83% and temperature at a near-constant 58 degrees Fahrenheit. Proper air circulation is crucial as moisture moves from inside the meat out to the surface and must be dried to prevent the growth of pathogens. Always use a scale to measure meat and ingredients: curing is a game of weights, and even a few grams or ounces can make or break your finished product. Specific types of curing will have different weight ratios, but once you've mastered the art of percentages, you can apply those curing ratios to any piece of meat your heart desires.