The Power of Staged Fermentation - Sour Grapes

Progression of the beer from: Day of grape addition (left) to 4 months later in the glass (right)

I am a bit of an experimentalist at heart, and one area in which I do a lot of "experimental" brews is using the staged addition of pure cultures of wild or commercial yeasts & bugs, pitched at varying times, to produce unique sour beers that cannot be produced through conventional brewing techniques. I've made beers with similar complexity to classical sour beers using staged-addition of bugs, but that's not what this post is about. Rather, this post is about using these methods to make good beer from difficult ingredients. In this case, wild grapes.

Wild grapes are pretty common place across North America, and they come in two "flavours" - European wine grapes that have escaped the vineyard and native species of grapes. Wild European grapes are pretty similar to the grapes you buy in the grocery store, and can be used as would any other wine grape in sour beer brewing. Truly wild grapes are another beast. In fact, my first attempt to brew with these turned a rather lacklustre 2-year old golden sour into an unpalatable mess. Thankfully I only added grapes to one gallon of that beer, and rescued the rest with a more classical cherry addition! There have been attempts since, and none (until now) were worth writing about.

There are nearly 70 species of wild grapes native to North America, so I'm not sure how true the following statements will be for brewers in other regions of N. America (or elsewhere), but for people in Ontario and the north-eastern US, this should be relatively accurate. The three species of wild grape native to my area (Vitis riparia, V. aestivalis and V. labrusca) are quite different from their European cousins. These grapes are much more intense than their European cousins; while the juice of European varieties are generally used to make wine undiluted, our local wild grapes need to have their juice diluted between 1:2 and 1:5 to produce a wine with a tolerable taste. The grapes themselves are quite small (0.5 cm diameter or smaller), have a very thick and tannic skin, have a much higher malic acid content, and have a much larger seed portion (relative to the amount of fruit) compared to their European cousins. And it is those characteristics that make them hard to incorporate into sour beer - essentially, enough grapes to give a nice grape flavour also imparts a lot of tannins, malic acid and grape-seed character.

Tannins are astringent and drying, and while nice in small amounts, they can quickly become overwhelming and unpleasant. Indeed, tannins are often made by plants for the purpose of deterring animals from eating the plant - the term "tannin" comes from their ability to tan leather, so you can imagine how excess amounts make your mouth feel. Malic acid is also quite harsh - almost as harsh as acetic acid - and like tannins can be pleasant in small amounts but becomes harsh and overwhelming quite easily. The seeds of grapes are also problematic - they contain some earthy and woody flavours that are pleasant, but the high seed content of wild grapes means these characters can be somewhat strong, and in my experience, clash with brett phenolics.

My attempts at using these grapes in conventional sours failed because of these characteristics - the malic acid would make an already acidic beer far too acidic and harsh, the seed character would amp up the funk, which in turn clashed with the high levels of tannins. Even pressing the grapes for juice doesn't solve these issues (aside from the grape seed flavour) to any meaningful extent. But where traditional sour brewing methods failed, "experimental" methods succeeded.

More Below the Fold

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A Quick Caution

Before I go into the meat of this post I want to quick caution readers about a potential risk of collecting wild grapes. All species of wild grapes are edible, but there are two similar-looking plants which are toxic - moonseed and virginia creeper. So it is very important that you know how to tell them apart. Because the morphology of wild grapes varies across the 70 or so species found in North America, and I believe there is also multiple species of moonseed and virginia creeper, I'm not going to post on how to tell them apart - rather, I'd recommend you look for a local (to you) source of this information, or find an experienced grape connoisseur to help you out.

If you're not sure what you have, don't pick it.

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Conceptualisation and Recipe

This recipe involved some planning on my part, as the recipe and brewing method required that 1) I be ale to control the degree of acidification to a high degree, 2) that I be able to reduce the malic acid content of the beer, and 3) that the Brettanomyces added to the beer not be overly phenolic. If I could achieve that then I should be able to make an intensely fruity beer with the grapes. The later goal is easy - B. claussenii is not overly funky and should act to enhance the fruit character of the grapes. But requirement 1 & 2 are a bit more difficult.

The solution to requirement #1 is a kettle sour - sour the beer to the desired acidity, then kill off the Lactobacillus by boiling the beer. However, the only way to address requirement #2 is Lactobacillus - most lactobacilli can engage in malo-lactic fermentation, in which harsh malic acid is converted into softer lactic acid. As luck would have it, a local brewer friend of mine had recently isolated the ideal Lactobacillus for solving this issue from a wild ferment - it produces a nice but not overly acidic acidity when used in the kettle, and was of a (suspected) species that is a malo-lactic fermenter.

The recipe has already been posted; I did a double-batch Berliner Weise back in September, half used to make a really excellent dry-hopped Berliner Weisse, a small amount used to try an experimental yeast, and the other half used to prepare this beer. The recipe formulation was fairly straight forward - conventional Berliner Wisse grain bill, no kettle hops, with the wort pasteurised following the sparge but not following souring.

The half set aside for this beer was fermented with US-05 following souring. As it was souring wild grapes were picked, washed, destemmed, and frozen overnight to release their juices. 2.5kg (5.5 lbs) of the uncrushed grapes were then added to secondary, along with a pitch containing three different B. claussenii isolates.

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Ageing

As you can see in the header image, within minutes the grapes had stained the beer a soft purple, which darkened dramatically over the ~3.5 months the fruit was left in contact with the beer. One month into secondary and the beer became what I had feared - harshly malic and tannic - but the Lactobacillus did its job and over the next few months reduced the malic character, eliminating it completely by packaging. In parallel the fruitiness of the beer has increased - how much of that is due to the Brett, and how much is an apparent increase in fruitiness due to decreasing harshness of the beer I cannot say, but it is nicely fruity. Unlike previous batches a strong seed character did not appear - perhaps because the grapes were not crushed this time, or perhaps because its a different species of grape or perhaps even terroir - the birds had denuded our normal picking area, forcing us to pick grapes on the opposite side of the road. Maybe its even an effect of the particular type of Brettanomyces used. Regardless, this aspect of the beer is not as developed as originally envisioned.

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Tasting Notes

Alright, that was a lot of writing to get to what was supposed to be the feature of this post - the tasting notes.

Appearance: The beer pours with a deep red body and pink head. Even though this beer was kettle soured, it has a persistent and rocky head.

Aroma: Grapes and lactic acid dominate the aroma of this beer.

Flavour: The flavour of this beer is excellent. The beer is notably sour - much more sour than the dry-hopped version of the beer thanks to the malo-lactic fermentation, but the sourness is balanced and smooth. I'm not sure if this is a product of the strain of lacto used, or because of lingering acids from the grapes, or because of flora from the grapes, but the acidity more complex than the 1-dimensional acidity I normally expect from kettle souring. Alongside this acidity is an intense fruitiness - the fruit character is unique and hard to describe, but is far closer to a blend of blueberries and raspberries than grapes/wine. If you've ever had wild grape wine or jelly you'll recognise the taste. This intense fruitiness provides a sweet character, despite the dryness of the beer (FG of 1.002), which nicely balances the acidity. What is missing though is the expected character of the grape seeds; as I mentioned above I was expecting this character to be intense, and dialled back on the brett to accommodate this. However, the seed character is completely absent, leaving this aspect of the beer wanting. I've bottled a portion of this batch with some B. lambicus in the hops that some balancing phenolics will form in the bottle. The aftertaste is an intense fruitiness and lingering sourness.

Mouthfeel: The higher acidity of this beer produces a slight puckering effect, with the combinatino of acid and carbonation producing a "sizzling" sensation on the tongue. The tannins from the grapes provides additional mouthfeel, so the beer feels thicker than its extremely low gravity would suggest. The beer finishes dry and crisp and not at all watery.

Overall: Overall this is a very good beer and one that I am quite proud of. The beer has an intense sourness which is nicely balanced by an intense fruitiness. It is crisp and refreshing, but complex enough to make it a beer to drink slowly and savour. What is missing is some phenolics, with either a more intense brett character, more grape-seed character, oaking, or some combination of the three required to provide a bit more interest in the background of the beer.