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Fermentations Apart: Selecting different yeast for different jobs

Fermentation is undoubtedly the most important part of homebrewing. The way that brewer’s yeast convert wort into beer is absolutely magic. As the yeast consume sugar to produce ethanol and carbon dioxide, their enzymes interact with compounds from the grain and hops to create potent aromatics. While the brewer can shape the fermentation through microbe selection, temperature, aeration, pressure, and adjuncts, sometimes it also makes sense to conduct a separate prior or parallel fermentation of a single ingredient to generate flavors otherwise impossible to achieve within the constraints of the alcohol, water, and pH of beer.

Several staple craft-beer flavorings ferment as part of their normal processing; e.g. coffee, cocoa, and vanilla. Few people, however, have access to the raw materials to carry these fermentations out at home. One fermentation option that can be done at home is rye bread, which is the basis for kvass (see “Kvass Revival” in December 2010 BYO). For this article I want to start by tackling an even weirder home-fermentation: Acorns!

I also want to discuss some of the benefits of split fermentations, which allow you to exert additional control by blending two finished products together to suit your palate. Specifically, fruit wines are a perfect splitting opportunity and a convenient technique to bypass many issues that nag traditional fruit beer methods, especially at more aggressive fruiting rates.

Fermented Acorns

The Homebrewer’s Almanac (Countryman Press, 2016) is one of my favorite brewing books. Written and photographed by Marika Josephson, Aaron Kleidon, and Ryan Tockstein of Scratch Brewing in Ava, Illinois, it details the huge variety of approaches that they developed to infuse their beers with local and foraged ingredients. One technique that captivated me was dry-fermenting acorns. The authors describe the resulting aromas as “[R]um, raisin, plum, bourbon, Madeira, all of the most amazing smells anyone could hope to get from oak.” All of that character from something you can pick-up off the ground for free!

The century-old white oak in my front yard cooperated during fall 2017 by dropping buckets of acorns; more than I’d ever seen from it. I gathered several pounds soon after they landed, before the squirrels got to them. My first step was to sort through my haul, discarding any that were cracked or otherwise damaged. I placed the keepers in glass dishes arranged in a single layer and allowed them to air dry indoors for a week. This step is essential as excess moisture can foster the conditions for future mold growth.

I discovered that a few of my acorns contained weevil larva. It was easy to spot the round exit holes and to discard the acorns that larva had destroyed. What I missed on my initial inspection were acorns with pinprick blemishes where eggs had been laid.

When I had the opportunity to visit Scratch a few months later on a drive from St. Louis to Indianapolis, I saw huge jars of acorns in their tasting room; they mentioned that luckily they had not experienced any weevil issues. Exactly what pests you deal with will depend on your location.

After a week, I moved the dried acorns to lightly closed mason jars without addition. The wild yeast and other microbes resident on the acorns do the work. If you seal the lid completely, make sure to burp the jars the first few weeks to release any carbon dioxide pressure. After ten months in a cool basement the aroma was a combination of apricot, distillery barrel-room, and old library books. While the exterior of the acorns was largely unchanged, the meat had turned from khaki to leathery brown. Exactly what process causes this change isn’t understood, but I’d guess a combination of ethanol/CO2 fermentation from yeast or bacteria along with a slow Maillard reaction between the proteins and carbohydrates.

I brewed a beer with compatible flavors for the acorns: A rye sour somewhere between English old ale and Flemish oud bruin. I pitched East Coast Yeast Oud Brune, which contains both Lactobacillus and Saccharomyces but no Brettanomyces. Brett can yield so many wild flavors that I was worried it would obscure the aroma of the acorns. A sour beer is also less likely to be negatively effected by the microbes from the acorns.

I reached out to Head Brewer at Scratch Brewing, Marika Josephson, to see if she had any updates to the acorn process since publication. She responded, “[W]e did 6 or 7 experiments last year to try to figure out the best way to infuse their flavor. Ultimately we decided that cold steeping in secondary (in a refrigerated space) and warm steeping (at room temp) was the best way of preserving the incredible flavor and aroma. Steaming and boiling the acorns before adding them to the beer in an attempt to pasteurize extracted quite a bit of tannic bitterness. In all cases we did break up the acorns into chunks first to help add surface area for more extraction–just bashed them up with a mallet of some kind.” So once the beer was soured, I wacked one pint (0.46 L) of the acorns with my mini-sledgehammer, splitting them in half. I dropped the meat and shells into a stainless-steel mesh tube weighted with glass marbles; this is the setup I use for keg hopping. After a weeklong infusion, I kegged the beer.

The acorns added wonderful depth of flavor, replacing some of the character that could have been provided by oak cubes, but with more depth and less “woodiness.” Despite a lack of long-aging, the beer had leathery notes I associate with well-stored oud bruin.

Fruit Wines

The ratio of fruit used in commercial sour beers is approaching the point of saturation. Fruit in absurd quantities can lead to results close to fruited mead (melomel). For example, Side Project Brewing in Maplewood, Missouri adds 6 lbs. of black raspberries for each gallon (0.72 kg/L) of base sour beer to create Fencerow. The result is a deliciously-intense fruit flavor that reveals little of the beer behind it.

Another approach to adding fruit flavors to beer is to directly add wine to your base. While commercial (grape) wine is an easy addition to replicate the flavors of wine-barrel aging or a grape-must addition, it is not the only option. You can ferment your own fruit, and then blend it into the beer to suit your tastes. Sour cherries for a Flemish red, or peaches for an IPA?
There are several advantages to fermenting fruit separately from the base beer:

  1. The best yeast for the beer may not be desirable for the fruit. Wine yeast strains are selected to free bound aromatics from fruit and generate esters that enhance the perception of fruit. By fermenting the fruit separately, you can tailor the fermentations for both fruit and wort. See “Brewing with Wine Yeast” in May/June 2018 BYO.
  2. The carbon dioxide released during fermentation carries aromatics with it. By adding fruit to the primary fermentation, you scrub more aromatics because of the combined fermentation of malt and fruit sugars.
  3. Long exposure to fruit skins and seeds can be beneficial in some cases, but in others produces off-flavors. I dislike the toasty “seedy” flavor that raspberry beers develop during long-term contact with the seeds.
  4. Your beer may not be ready for fruit when the season is right. Fruit can be frozen and vacuum bagged if you have room in your freezer, but making a fruit wine can save time and effort.

Often fruit “country” wine recipes call for a considerable amount of refined sugar to increase the amount of alcohol. This is not necessary in the context of blending with beer. I suggest skipping this step as the fruit contains enough simple sugars. Starting with whole fruit, simply separate liquid from pulp. I find it most convenient to strain the liquid before fermentation to limit the risks of oxidation later.

You can use a juicer, but they can be difficult to clean let-alone sanitize. In a food processor or blender, puree and then squeeze ripe fruit through a sanitized mesh bag. Frozen fruit may not even need to be pureed. At this point you can add metabisulfite and wait 24 hours for it to kill any wild microbes or pitch the wine or brewer’s yeast that suits your palate immediately. As a simple alternative, you can ferment commercially pressed and pasteurized fruit juices in the bottle they come in (pour out a sample to make room for the kräusen). If you’d rather not ferment the fruit alone, add all of the fruit to half of the beer, then blend the two back together to taste once the sugars in the fruit are fermented.

Many homebrewers try their hand at hard cider, which despite the name is easy to make. If you do, you can add your homemade cider to a batch of beer. At Old Trade Brewery in Brandy Station, Virginia, my friend Garrett Thayer brews Malum with that process. He combines 40% cider, which he ferments with Safale S-04, with Pilsner or Kölsch in the brite tank. This approach cuts the bitterness and malt flavor, creating an approachable and refreshing beer with a wonderfully fresh apple aroma. You can do the same in a keg or bottling bucket at home. If you’re not sure whether or not this idea sounds delicious, mix cider and beer in a glass to explore different base beers, apple varieties, and ratios. Apple cider blended into tripel is wonderful, and perry (pear cider) can be especially good with Belgian golden strong.

Similarly, there is nothing to prevent you from making mead and later blending it with a base beer to create a honey beer or braggot (depending on the ratio). In addition to affording control, blending provides an easy course to experiment how a varietal honey influences beer flavor.

Final Thoughts

Many homebrewers are fermentation nerds, and it is fun to combine elements and ingredients from the various traditions. You could make a beer-washed cheese, a kettle sour with yogurt whey, or a sour beer with your sourdough culture. Homebrewers brag about using the “same” ingredients as the best breweries in the world, but it can be even more fun to use ingredients that the best breweries in the world don’t! Fermenting fruit and acorns are just two examples of the range of fermented flavors:

White miso for salinity in a gose?
Tepache for fruitiness in a blonde?
Sake to bolster a West Coast double IPA?

Get weird with your fermentations and your beer!

Recipe

Acorn Oud Bruin

(5.5 gallons/21 L, all-grain)
OG = 1.046 FG = 1.010
IBU = ~2 SRM = 18 ABV = 4.7%

Ingredients
6 lbs. (2.7 kg) Briess Pilsen malt
2.5 lbs. (1.1 kg) Weyermann Munich I malt (6 °L)
1.5 lbs. (0.7 kg) flaked rye
0.5 lb. (0.23 kg) Dingemans Special B malt
0.25 lb. (113 g) Weyermann Carafa® Special II malt
0.625 oz. (18 g) Willamette hops (aged) (60 min.)
1⁄2 Whirlfloc tablet (50 min.)
East Coast Yeast ECY23 (Oud Brune) yeast
2 cups (0.46 L) fermented acorns
3⁄4 cup corn sugar (if priming)

Step by Step
Begin the acorn fermentation process about 1 year prior to brew day. Dry out acorns for one week on baking sheets or other suitable surface. Place the acorns that are free of defections into ball jars and cover, burping the ball jar(s) every week or so. Store in a cool, dark place for 8-12 months.

Heat 5-gallons (19-L) water to target mash temperature of 157 °F (69 °C) for 30 minutes. Run off into kettle. Sparge to collect 7.5 gallons (28.4 L) of wort. Boil for 90 minutes, adding hops and Whirlfloc as noted. Chill to 66 °F (19 °C). Aerate the wort and pitch the suggested blend, or a blend of English ale and Lactobacillus of your choice.

Allow the fermentation to warm to 68 °F (20 °C) until fermentation appears complete. Place the fermented acorns on a piece of aluminum foil and tap each with a hammer to split. Add acorns including shells to the fermenter either loose or bagged and weighted. Leave at the same temperature, tasting weekly until the desired flavor is achieved. Either keg or bottle the beer to achieve 2.3 volumes of CO2.

Issue: November 2018