Lactobacillus curvatus

Lactobacillus curvatus wears its shape in its name, a lactic milk-rod, from lac, milk, and bacillus, little rod, that grows characteristically curved or crescent. In 2020 the vast and unwieldy genus Lactobacillus was divided by Zheng and colleagues into twenty-six genera, and curvatus, with its partner sakei, was moved into the new genus Latilactobacillus; a curesmith will meet both the old and new names on culture labels and in the literature. It is a Gram-positive, facultatively heterofermentative bacterium of the L. sakei group, and its defining trait for the craft is a taste for the cold: it thrives at the cool temperatures European dry-curing favours, where the warmth-loving pediococci would stall.

Its rise is bound to that of L. sakei, and the two are best understood together as the twin acidifiers of European charcuterie (the wider story of controlled fermentation is told under starter-culture). Where early European makers first reached for nitrate-reducing micrococci and even regarded lactobacilli with suspicion, it became clear that a chosen, well-behaved lactic bacterium was the surest engine of a safe, cool ferment, and curvatus and sakei, isolated again and again as the dominant flora of successful dry sausage, became the natural choice.

Its work is acid. It ferments the added sugar, dextrose above all, to lactic acid, and that falling pH does three things at once: it firms the protein bind that holds the sausage together, it lays down the clean tang of a fermented product, and it competes the unwanted organisms out of house and home. On the six-carbon sugars it ferments cleanly to lactic acid; on five-carbon sugars it takes a mixed path to lactic and acetic acids, which is one reason the choice of sugar shapes the finished tang. Many strains carry a further gift, the ability to make bacteriocins, curvacin and its kin, natural antimicrobial peptides that hold Listeria in check through the vulnerable first days before acidity and drying have taken hold, which is why curvatus and sakei are prized as protective as well as fermenting cultures.

In use it is chosen for the cooler, slower ferments of European charcuterie and supplied freeze-dried or frozen in a commercial blend, almost always alongside a colour-and-flavour staphylococcus. Rehydrated in unchlorinated water and mixed evenly through the meat with its sugar, it works best at roughly 20 to 25 degrees Celsius. Where an American maker might reach for a fast pediococcus and a warm ferment, a European maker reaches for curvatus or sakei and a cool one, and lets flavour build slowly.