Vinegar Science pt. 4: Slow Malt Vinegars with Nordic Flavours

by Arielle Johnson


Traditional malt vinegar, most commonly doused on fish and chips, is not regarded with much culinary interest. In our quest for developing Nordic vinegar, we found this widely produced, commercial malt vinegar as a source of inspiration for developing beer-base vinegars that held the potential for more complex and interesting flavors. The experimentation consisted of two types of malt-beer bases. For one, we mashed and fermented pale ale barley malt in a style similar to home-brewed beer. For the other, we brewed a koji-beer by creating a mash as if koji were malt. This method of brewing and fermenting koji proved unsuccessful, so we tried using another type of grain-based alcohol as our base. We created barley koji sake, which yielded much better results. To these malt vinegar bases we added flavourful foraged Nordic botanicals and allowed the vinegars to continue to slowly ferment for another 3-4 months.

After our descriptive analysis, we wanted to experiment further, especially with approaches to alcoholic fermentation and flavour addition. Could we better incorporate Nordic flavors like pine, liquorice, and juniper, as well as things like seaweed, which we have used at Nordic Food Lab for other flavour and functional purposes, into robustly-flavored, well-rounded vinegars with stability and aging potential?

The obvious next step was to explore a 3-stage process: a sugar-to-alcohol yeast fermentation, followed by the addition of non-fermentable, highly-flavoured ingredients (either during or after fermentation), and then a slow (3-4 month) passive fermentation into vinegar following the addition of raw vinegar as a starter culture.

Sugar and Alcohol

Initial ideas for sugar sources that could contribute a pleasant but not overpowering flavour to a vinegar, that would be available in the winter (in keeping with our interest in seasonality), and that would ferment nicely were apple juice and birch syrup. Apple juice could be reduced into a syrup through boiling, and then mixed with uncooked juice to reach a sugar level that would yield a relatively mild vinegar. Similarly, birch syrup, which has a much fruitier flavour than maple syrup, could be diluted to a comparable level. Both of these sugar sources, we reasoned, should provide, if not a blank canvas, then at least a foundation to begin showcasing other aromatic ingredients.

We were separately but simultaneously experimenting with an insect-hopped ale, and realized that beer malt was another near-perfect base for new vinegars. Relatively inexpensive, plentiful, covering a huge range of flavours (all beers, by definition, involve malt; the flavour range between, say, lagers, lambics, pale ales, baltic porters, and quadrupels speaks to the versatility and diversity of malting as a process), and fairly easy to work with, malt also allowed us to begin exploring vinegars made from more specialty beers. Traditional malt vinegar is one of the most widely-produced commercial varieties of vinegar, but despite its ubiquity on fish and chips, the commercial versions are not so interesting culinarily. This next-stage project would focus not on getting the cheapest vinegar out of malt, but exploring malt’s potential for producing and supporting complex and delicious flavours.

We mashed and fermented pale ale barley malt (augmented with a variety of other malts) in batches of 8 to 30L with techniques likely familiar to home brewers. Using some handy online calculators, we figured out how much malt we needed to obtain a certain sugar content. About 80% of malt mass can be converted into sugar, and somewhere between 60-90% of this sugar can be extracted out of the grain – which in turn yields a particular alcohol level and, after acetic fermentation, a particular concentration of acetic acid. We ground the malts in a grain-grinder, small enough for an efficient extraction but not so fine that the particles would mix with water and cause a ‘stuck’ or slow fermentation.

The malt and hot water were mixed together in an insulated container and held at a temperature between 64 and 69°C, where the amylase enzymes in the malt are most active, chopping long starch molecules into small sugars which yeast can metabolize into ethyl alcohol. At the lower end of this range (64-65°C), beta-amylases are more active, leading to higher proportions of disaccharides (called maltose), which are wholly digestible by yeast. At the higher end (67-69°C), a different form of the enzyme called alpha-amylase becomes active, and this indiscriminate digester of starch yields maltose molecules as well as many other larger oligosaccharides, called dextrins, which can contribute viscosity, body, and sweetness but are not digestible by yeast. As such, a slightly cooler mashing will yield a drier, higher alcohol beer, while a hotter mashing will produce a sweeter, more viscous, and less alcoholic beverage. For most of our batches we stuck to the lower range, but for a few we heated the mash up to higher temperatures at the end to get a bit more body and sweetness in our resulting vinegars.

Many times, projects that may seem new actually end up being reinterpretations of long-held traditions. In taking malt through the brewing process, for example, the question of to hop or not to hop invariably came up. For vinegars with a distinctly beer-like taste it would make sense to hop the beer, but we also wanted to make at least some vinegars whose flavours expressed the other aromatic ingredients along with the malt. A little research into the history of brewing shows that the un-hopped beers we made were actually much closer to the medieval and pre-early-modern version of ale, which didn’t contain hops until somewhere between the 11th and 16th centuries. Totally unhopped, alcoholic malted grain beverages, at least in England, were called ales, to differentiate them from hopped versions imported from Holland, which were called beers. In fact, adding things like pine needles, juniper wood and berries, and other foraged herbs to the fermenting or finished wort actually reflects a much earlier style of brew called gruit (which often also included bog myrtle, mugwort, yarrow, and/or heather), or the still-popular Finnish beer sahti, made with juniper berries and filtered through juniper twigs.

At the same time that we were developing beer vinegars, we also started playing with roasting koji, which caramelizes the sugars in the koji and creates new flavours, similar to coffee or chocolate but definitely its own creature. Our friends at the Noma test kitchen put this to excellent use in a mole dish (a diverse group of sauces in Mexico, some of which involve cacao), and we collaborated on different ways to get roasted koji into vinegar – making alcoholic teas out of it, pine-vinegar-1.0 style, and also adding it to a beer mash with regular malt. By exploring different roast levels, ratios, and fermentation routes, we made koji-beers in a variety of colours, strengths, and flavours that then slowly, with the addition of foraged botanicals, continued on their way to becoming vinegars. For the recipe for Ben’s first roasted koji pale ale, check out our post on roasting koji.

It seemed logical to also try brewing with barley koji directly, rather than as an adjunct to a malt fermentation. Treating the koji like a malt – mashing it with water at pro-amylolytic temperatures (64-68°C) – was unsuccessful, as it had quite a low yield and also seemed to induce some proteolytic action, producing a funky taste that wasn’t altogether pleasant. Making a barley sake, on the other hand, worked quite well, and we’re excited to see what acetifying this will lead to. Unlike the sugar extraction through mashing and heat involved in beer-brewing, that in sake-making involves Aspergillus oryzae grown on grain (in our case, barley) to make koji, which is sweet and full of amylolytic enzymes, and then mixed with cool water, more steamed barley, and yeast. The koji will slowly convert the starch of the steamed barley into sugar, and the yeast will metabolize the sugar as it is transformed into alcohol. Then, the sake is strained off of the lees of grain, mold, and yeast, and these lees – which still have some enzymatic activity – can be used for pickling (as in the traditional Japanese kasu-zuke, sake-lee pickles) or other purposes.

After brewing and fermenting the beers/gruits with yeast under an airlock, we began splitting the larger batches and adding aromatic ingredients, as well as starter vinegar, which we kept at 20% in order to control our comparisons from batch to batch. Each vinegar batch gets a cloth lid so oxygen can get in, and we are keeping them in a safe place until later, when we are planning to do a more formal sensory analysis.