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