21/09/14 | Posted in pickled vegetables by Bronwen Percival

The Sirk family own and run the Trattoria La Subida outside the town of Cormons in Friuli-Venezia Giulia, nestled in the hills only a few miles from the Italian-Slovenian border. Led by Mitja’s father, Josko, the Sirks ferment their local Ribolla Gialla grapes into a very unusual and delicious long-macerated and barrel-fermented wine vinegar. 

In the last decade, the region has risen to prominence for its production of ‘orange wine’: wine made from white grapes that undergo an extended maceration on their skins. During this time, tannic polyphenols from the skins infuse the wine, just as they would in a red wine, giving orange wine its distinctive colour and texture. The Sirks’ vinegar is special because it is the acetic analogue of this rare orange wine: both the natural alcoholic and acetic fermentations takes place in a slurry of white grape skins and juice, leading to what is perhaps the world’s only ‘orange vinegar.’

Mitja Sirk in the vinegar production room.

Mitja told me about the process: “We always use our local grape variety, Ribolla Gialla, for three reasons: firstly it is our local grape which brings us back to our land. It also has a very strong skin, one of the strongest skins, so for our type of long macerations, where the whole process from juice to vinegar is done in contact with the grape skins, it’s very important. A few years ago we tried with another local grape, Tocai Friulano, which has thinner skins, but it was terrible! Finally, the sugar level and then the alcohol level is low, and the acidity is high, so Ribolla provides an easier place where the acetic acid bacteria can grow and develop.”

A lot of emphasis is placed on the use of ‘natural’ fermentation techniques, from the initial wild yeast fermentation that transforms the grapes’ sugars into ethanol, and then the second bacterial fermentation in which members of the genus Acetobacter metabolise that ethanol to puckeringly-sour acetic acid. The Sirks use their own vinegar mother—‘la madre’ in Italian—to start their fermentations each year, adding some vinegar to the grape slurry just as the alcoholic fermentation is coming to an end. Unlike the relatively quick alcoholic fermentation, which takes place in a matter of days, the acetic acid bacteria work much more slowly, with the bulk of the fermentation occurring over the following summer. After eleven months, just before the next harvest of grapes is ready to come in, they press the slurry to separate the vinegar from the spent skins, and decant it into small oak barrels, where it ages for two years before bottling.

The La Subida vinegar is very strong, with more the twice the minimum acidity required for vinegar to be sold in the United States. “In Italian law, vinegars must have less than 1% alcohol, and in the natural way that is very hard to do. We are bottling the vinegar between 8.5 and 9.5 degrees, with under 1% alcohol, and so we are very happy with this.”

Grape vinegar fermenting happily under ‘la madre’.

It was not always such smooth sailing. A few years after they increased their production, taking it from the status of a family pastime to a tiny side business, they ran into problems. Mitja speaks of a succession of difficult vintages starting with 2012. “The next summer [when the acetic acid fermentation would normally finish] half of the barrels in the cellar were working very differently; no mothers were forming and the alcohol was slowly going down but without increasing the acidity. That year we made only half of the production, and in 2013 we still had more or less the same problems; some barrels were working and some others not.

“We asked for help from the University of Udine, the University of Modena, and the University of Ljubljana in Slovenia. All three said the same thing: we were unique that we were able to make the vinegar as we had made it with no problems. We were adding absolutely nothing, no yeasts, no sulfur, nothing. At the end of [alcoholic] fermentation, at the beginning [of making vinegar] we were adding just a very small amount of old vinegar to start the second fermentation. During winter time it was not productive, then in summer time the first year was very good, and the second summertime was very important to finish the process.

“We discovered a couple of problems with our process. In 2013, spring and summer were not very hot, and the temperature was going up and down very frequently…that was very bad for the bacteria, they would start working for a couple of hours and then during the night when the temperature in the cellar would go down to 12-14⁰C they would stop again.

“The second very big problem that the scientists told us was that our addition of the old vinegar was really very low. Usually, other producers would add half-half: half wine and half old vinegar. Then when the fermentation was going, they would add that to the other barrels.” Adding more vinegar starter raises the acidity of the wine to a point where the acetic acid bacteria could function more comfortably, in much the same way as successful kombucha propagation requires a ‘push’ with some pre-acidified liquid. “The points that the universities were telling us: please try to keep acidity higher than 2.8% and try to keep the temperature above 20⁰C.”

For the 2013 harvest, the Sirks added the capacity to warm the grape-wine slurry within the barrels, to ensure that it stays within the correct temperature range during the critical phase of the acetic acid fermentation. They also began making a bulk vinegar starter from their mother culture, starting the bacterial fermentation off with some juice in a stainless steel tank until it is proceeding happily. Then they use this bulked-up starter to inoculate the barrels with a much higher dose.

Mitja is quick to state that the long maceration process gives their vinegar its character, but also recognises the importance of their house vinegar culture. “Last year we tried a different bacterial strain on some juices, because one of the universities was saying that we should try to use another bacteria. The vinegar was completely different; when we were doing tastings this year, we were very disappointed in the trial vinegar; it was not as complex.”

Aceto di Uva. Image courtesy of La Subida

The Sirks are one of only a few families still making vinegar using slow, artisan methods. “We know of about twenty producers using very low-technology approaches, but nobody is surviving with the vinegar. Of our four friends who are also making vinegar: one is a honey producer, two make wine, and there is one that selects and sells Parmigiano-Reggiano and Balsamic vinegar. My family are restaurant owners. Together we try to promote and create these new ideas about our products.”

La Subida grape vinegar is intensely aromatic. “When it is pressed it is very difficult to taste and ‘rude,’ but after two years in the barrels it becomes very round and elegant. The complexity of our vinegar is very similar to the complexity of wine. The flavour of a plain wine vinegar is simple and just based on the acidity, like rustic clothing. Our grape vinegar [fermented and acidified on the skins] is much more complex, and sometimes reminds of minerality or saltiness. The aromatic part is very strong, very polished.”

Mitja’s family and the producers group they have helped to organise are trying to change the way that people regard this ubiquitous kitchen staple. “There is a big lack of culture about vinegar. Our big focus was the uses of vinegar: very few people eat salad without vinegar, but we also like using quality vinegar on many other dishes. We came up with 100 different ways of using vinegar ‘out of the salad bowl.’ The idea is to use an acid taste on something that is too sweet or fatty: in our home nobody eats eggs without vinegar on them since 2006.” The restaurant also makes a stunningly delicious vinegar sorbetto.

Many thanks to Mitja and his family for their tremendous hospitality and for spending time showing us around the vinegar house. More information about their vinegar production and their delightful and welcoming Michelin-starred restaurant can be found here.

Post by Bronwen Percival.