A cloth soaked in salt water builds a rind

A linen cloth in a cave

Michel de Montaigne, travelling in Italy in the second half of the sixteenth century, wrote down how a square cow's-milk cheese was made. It was set on straw and rye, salted and carried to caves to ripen. There it was turned and cleaned with a linen cloth soaked in salt water. The cloth is the important part. Wiped over and over, the cheese stops being a plain block of curd and becomes a surface that someone tends.

That surface defines a whole family. Washed-rind cheeses, also called smear-ripened, are not defined by their milk, their shape or their country. They are defined by a rind that is kept wet, salted and slightly slippery so that a particular community of microbes can live on it. The rind turns orange or pink, the smell becomes unmistakable, and the cheese ripens from the outside inward. Taleggio is the example followed here, with Époisses and Munster alongside.

Tired herders and monastic cellars

The old family name of Taleggio, stracchino, comes from the dialect word stracch, meaning tired. It was used of the herders coming back from the pastures. The earliest written mention that Italian cheese tasters cite is an 1872 treatise by Gorini. A regional account puts the origin in the tenth or eleventh century, as a way of keeping surplus milk, and cites a thirteenth-century reference to a stracchino quadro di Milano. The cool, damp caves of Valsassina and Val Taleggio have been compared with the French caves where Roquefort ripened. The protected designation dates from 1996. Neither the old tradition nor the caves are a proven first origin.

Monks left their mark on the family too. One theory, offered as a theory, is that communities who gave up meat favoured strong, savoury cheeses. Alsatian Munster is dated to as early as the seventh century and attributed to Irish monks in the Vosges who were taught by visiting Italian Benedictines. Époisses is tied to a Cistercian community in Burgundy. One account puts its beginnings in the early 1500s or the 1600s, another in the fourteenth century. Monks are said to have made it for nearly two centuries. By the early 1900s more than 300 farms made it, and wartime nearly ended it. In 1956 Robert and Simone Berthaut breathed new life into it, and it received its appellation in 1991. These are traditions told by cheese writers, and the dates do not agree.

A rind is a habitat

In 2014 a Harvard team led by Rachel Dutton sequenced the microbes on the rinds of 137 cheeses from 10 countries. Twenty-four genera of bacteria and fungi turned out to be the dominant members. The rinds fell into three community types, and the types formed regardless of geography. Dutton's conclusion is that the environment the cheesemaker creates drives the community. The team also rebuilt the community types in a simple laboratory system. For a washed rind, that environment is salt, moisture, a cool room and a regular wash.

Yeasts open the door, bacteria follow

The starter bacteria that made the curd turned lactose into lactate, and some of the bacteria that later dominate the rind cannot grow on a surface that acid. Yeasts come first. Debaryomyces hansenii, Geotrichum candidum, Candida catenulata and Yarrowia lipolytica average about ten thousand colony-forming units per square centimetre on a smear-ripened rind, and their counts peak in the first days at up to ten million. They feed on lactate, and by consuming the acid they deacidify the surface.

One 2006 study of a model cheese is reported to have found lactose used first, in step with the exponential growth of D. hansenii, and about 90 percent of the lactate gone after 21 days at 10 °C. A model cheese in a laboratory is not a Taleggio rind, so treat those figures with caution. A later mathematical model of curd deacidification in a pilot chamber, run at 8, 12 and 16 °C and at 85, 93 and 99 percent relative humidity, followed the yeast and the lactose and lactate in core and rind.

Once the pH has risen, the smear bacteria take over. Brevibacterium, Corynebacterium, Arthrobacter, Glutamicibacter and Microbacterium appear, with Staphylococcus, Halomonas and Psychrobacter. Corynebacteria tolerate a pH of 4.9 and 8 percent salt and may make up as much as 70 percent of the bacteria in the smear. Microbacterium cannot grow below pH 5.8, which keeps it out until the deacidification is well along. By about day 12 the bacteria have climbed to a billion to ten billion colony-forming units per square centimetre, far more than the yeasts. A microbiology review places Geotrichum before the coryneform bacteria in this order.

A Taleggio study by Italian cheese tasters shows what the sequence leaves behind. The surface sits at about pH 6.2 and the centre at 5.0 to 5.3. The surface carries micrococci, yeasts and moulds, and breakdown of protein is the most visible of their effects. The outside is working on the inside.

Where the smell comes from

The smell of a washed rind is mostly sulphur. Surface microbes make sulphur compounds from two amino acids, methionine and cysteine, and the compounds concentrate at the rind. Methanethiol, hydrogen sulphide, dimethyl sulphide, S-methylthioacetate and ethional are typical of smear cheeses, and the key ones give the garlic notes of an intense example.

The best-studied producer is Brevibacterium linens. In 1979, eight strains isolated from cheese were all found to make methanethiol, dimethyl disulfide and 2,3,4-trithiapentane, and four also made S-methylthioacetate, described as an important aroma component of smear-coated cheeses. In 2004 the enzyme behind much of it was identified. Methionine-gamma-lyase splits L-methionine into methanethiol, alpha-ketobutyrate and ammonia. When the gene for it, mgl, was disrupted in the type strain ATCC 9175, thiol activity fell by 62 percent and total volatile sulphur output by 97 percent.

Other microbes add their own notes. Microbacterium, which appears late in ripening, also makes methanethiol. In one study Geotrichum candidum was associated with sulphur compounds, while D. hansenii was linked to alcohols and carboxylic acids. Yeasts also strip the amino group from amino acids, which yields keto acids and ammonia. All of this comes from laboratory strains and smear cheeses in general. Measurements of ammonia or sulphur compounds in Taleggio or Époisses themselves were not found.

What goes into the wash

In Taleggio's valleys the wash is salt water. Roughly every seven days during ageing the cheeses are sponged, which keeps the rind moist, soft and rosy and removes mould hyphae. The salt works twice. It favours organisms that tolerate it and holds back those that do not. The balance matters: too much salt can leave the smear whitish, and a surface that dries out points to too little.

The cloth also moves microbes from one cheese to the next. Some makers do this on purpose. In old-young smearing, mature cheeses are washed with saline and that saline is reused on young ones to hand over a ready-made rind community. Food-safety authorities criticise the practice and it is used less often now. Where it is still used, brushes are cleaned and the brine is renewed between ripening ages. Industrial brining before ageing runs at 19 to 21 percent salt by weight for 4 to 18 hours at 10 to 14 °C as general practice, and Taleggio uses 8 to 12 hours.

In Burgundy the wash for Époisses is salt water and marc de Bourgogne, a brandy distilled from grape pomace. No dyes may be used in its production, so the red-orange colour comes from the growth on the surface.

Taleggio in the cellar

Protected Taleggio ages for at least 35 days, and some ripeners prefer 45 to 50. The ageing rooms are kept at 85 to 90 percent relative humidity and 2–6 °C. The wheels sit in wooden crates on cotton cloth, and the wash comes about once a week.

The consortium reported 4,478,000 wheels in 2014, up from 4,163,423 in 2012 and 4,330,000 in 2013. About a fifth of them were exported, and roughly 8 litres of milk go into each kilogram of cheese. The scale has changed a great deal since the caves, and the washing has not gone away.

The risk that rides on the cloth

Listeria monocytogenes can grow well on red-smear surfaces, and old-young smearing raises the chance of spreading it from one cheese to another.

Laboratory work shows how uneven the risk is. In one study, 43 soft-ripened cheeses, 12 from raw milk and 31 pasteurised, were inoculated with a thousand Listeria cells per gram and held for 12 days at 8 °C. Growth differed a great deal from cheese to cheese. Raw-milk cheeses supported less growth, and growth rose with the abundance of Streptococcus thermophilus. The authors link industrial starter use to higher risk, but they found no clear mechanism. That result measures how fast an introduced Listeria grows, not how likely it is to get in.

A challenge study on the surface of artificially contaminated smear- and mould-ripened cheese found that water activity was not related to Listeria growth. Its authors argue for separate European rules for surface-ripened cheese and for results given per unit of surface area. A Swiss study inoculated cheeses from nine dairies with Listeria innocua as a stand-in. Acetic acid, lactose and glucose correlated with its growth, and the authors propose protective strains from the cheeses' own microbiota.

At the table

Taleggio is served at room temperature. The rind may be eaten, or scraped or lightly brushed first. Italian tasters pair it with onion soup made with dark beer, and with a red wine such as Valcalepio.

Époisses is eaten once it has reached room temperature, not warmed. At about 40 days of ageing the texture is described as like a pudding. Regional advice for Taleggio is to keep it in the refrigerator wrapped in a damp cloth for about a month, or to freeze it for up to six months.

What a rind cannot tell you

An orange rind and a strong smell are normal for this family. They are not evidence that a cheese is safe, and no surface appearance can show it. The American Cheese Society treats ripening as a controlled stage of cheesemaking with its own contamination risks, and raw milk, starter, the make, the ripening cheese and the finished cheese each need evidence suited to that stage.

What the research does establish is that the wash is a form of microbial management. The yeasts, the salt and the cloth shape which bacteria settle, and those bacteria make much of the aroma. What is still missing is measurement on the cheeses themselves: how much ammonia and sulphur a Taleggio or an Époisses really carries, and how Listeria behaves on them through a normal ripening.