By Harold McGee
These days, nitrates (Europe) or nitrites (U.S.) to suppress botulism bacteria are added to the mix of meat, fat, bacterial culture, salt, and spices, as is some sugar, at least part of which the bacteria transform into lactic acid. Fermentation lasts from 18 hours to three days, depending on temperature (60–100°F/15–38°C, with dry sausages at the low end) and sausage size, until the acidity reaches 1%, the pH 4.5–5. High-temperature fermentation tends to produce volatile acids (acetic, butanoic) with a sharp aroma, while low-temperature fermentation produces a more complex blend of nutty aldehydes and fruity esters (the traditional salami flavor). The sausage may then be cooked and/or smoked, and finally is dried for two to three weeks to the desired final moisture content. A powdery white coat of harmless molds and yeasts (species of Penicillium, Candida, Debaromyces) may develop on the casing during drying; these microbes contribute to flavor and prevent the growth of spoilage microbes.