Monday, December 10, 2018

Fermented Acorn - Sour Brown

The first week of October, DC posted a notice on our front door informing us that an arborist deemed the oak tree in our front yard hazardous. Up until that moment, it would have been illegal to cut down as a "heritage" tree (over 100" in circumference). They gave us 10 days to apply for a permit and have it removed. The tree had obviously been on the down-slope for the last 10 years, but this summer a large swath had gone brown mid-August and the rest in late-September.

I was sad to see the tree go, but glad I got to brew a beer with acorns foraged from it before it went!

Oak tree removal

Last fall, inspired as usual by The Homebrewer's Almanac, I collected acorns over a few afternoons. While fresh acorns are loaded with tannins, fermented they are said to take on a wonderful aromatics reminiscent of bourbon, Madeira, and plums. The various parts of any plant usually contain shared compounds (and flavors). It has become fashionable to cook with the "garbage" parts of plants (and animals) usually thrown away. While it takes more effort to prepare collard green stems or pork feet, it can be well worth it. While oak wood is used to age thousands of beers, its acorns, leaves, and bark are not nearly as popular.

I inspected each acorn to remove any that were cracked, or otherwise marred. I briefly rinsed them, and then arranged in a single layer on a shallow baking dish in the basement to allow them to dry.

Acorns before sorting and drying

Apparently my inspection wasn't thorough enough as I missed several small blemishes (example below) that indicated an acorn weevil had laid an egg inside.

Acorn Weevil hole

A week later, after discarding those where a larva bored out, I moved the acorns to five lightly sealed pint mason jars. I didn't add water, microbes, or anything else.

Fermenting acorns in mason jars

Over the next nine months in my 65F basement the acorns slowly fermented on their own. First producing carbon dioxide and the pleasant aroma of ethanol. Then slowly a more complex aromatics of apricot, chocolate, and bourbon. Exactly which microbes are responsible is a mystery to me.

When I visited Scratch Brewing last November (on my drive from St. Louis to Indianapolis for the BYO Boot Camp... next one is March in Asheville) I had the chance to assist Marika on a batch at Scratch, and see their jars of fermenting acorns. Luckily for them, Aaron told me weevils haven't been an issue!

Acorns fermenting at Scratch Brewing

By the following summer, my acorns were smelling like a combination of whiskey distillery, apricot orchard, and old library. While their exteriors were unchanged, the interior transformed from beige to leathery brown. Non-enzymatic browning, that is to say the Maillard reaction may be at work as with black garlic? While these processes are accelerated at high temperature, they still happen when cooler.

I thought an oud bruin-ish base would provide a solid foundation for those darker flavors. I added flaked rye for body and fermented with East Coast Yeast Oud Brune (which contains no Brett, only Sacch and Lacto). ECY Flemish Ale is still hard at work on the other half of the batch. Once the Oud Bruin was finished, I added a tube screen with one cup of the cracked (with a hammer) acorns. After a few weeks I added another cup to increase the flavor contribution.

Cracked acorns

I'm hoping to use the remaining fermented acorns in a small batch at Sapwood Cellars, but the TTB isn't going along with my plans... yet. They've directed me to contact the FDA. It's amazing how many weird chemicals are approved, when a food that people have eaten for thousands of years is not.

Requiem for an Oak

Smell – Even at the higher rate the acorn character doesn’t leap out of the glass. It does have a richer, more woody-fruity aroma than any other quick sour I’ve brewed. I get some of that old book smell mingling with the Munich maltiness. There is also a brighter stonefruit aroma that prevents it from being too heavy.

Appearance – Pretty amber-brown color. Mild haze. Retention of the tan head is OK especially for a sour beer, although nothing remarkable.

Taste – Firm lactic acid, snappy without being overwhelming. The fermented acorns add leathery and fruity depth to the flavor without stepping all over the malt. I’m pretty happy with this as a lower alcohol oud bruin.

Mouthfeel – The flaked rye really helped considering this is a low alcohol sour beer. Doesn’t taste thin or watery.

Drinkability & Notes – For such a unique beer, it is pleasant to drink. The flavors meld nicely and the acorns help to simulate in a way the effect of barrel aging and Brettanomyces.

Changes for Next Time – I’d probably go even more aggressive with the acorn-rate, really to show them off. The beer could be bigger, but more malt might obscure the acorns even more.

Finished acorn oud bruin


Batch Size: 11.00 gal
SRM: 18.0
IBU: 2.0
OG: 1.046
FG: 1.010
ABV: 4.7%
Final pH: 3.43
Brewhouse Efficiency: 72%
Boil Time: 90 mins

60.4% - 16.00 lb Briess Pilsen Malt
22.6% - 6.00 lb Weyermann Munich I
11.3% - 3.00 lb Flaked Rye
3.8% - 1.00 lb Castle Special B
1.9% - 0.50 lb Weyermann Carafa Special II

Mash In - 45 min @ 157F

1.25 oz - 8 Year Old Willamette (Whole Cone, 1.00 % AA) @ 85 minutes

11 g Calcium Chloride @ Mash


Whirlfloc Tablet @ 5 mins
2 Cup Fermented Acorns @ Fermenter

East Coast Yeast Flemish Ale
East Coast Yeast Oud Brune

9/29/17 Harvested five pints of acorns from the White Oak in my front yard. Allowed to dry open in the basement.

10/6/17 4 larvae of an acorn weevil hatched. Tossed any acorns with exit holes, and tried to identify all of those with small entry holes to toss. Moved remaining acorns to one-pint mason jars, attached lids, and returned to the barrel room for fermentation.

Brewed 7/9/18

7/29/18 Added 1 cup of acorns (split and in a mesh tube with marbles) to the Oud Bruin half.

8/18/18 Added another cup of acorns, loose, as the flavor wasn't there yet.

8/28/18 Racked Flemish half to secondary in glass.

9/9/18 Kegged acorn half.

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Anonymous said...

So this was 2 cups acorns to 5.5 gallons then?

The Mad Fermentationist (Mike) said...

You got it!

Anonymous said...

"Luckily for them, Aaron told me weevils haven't been an issue!"

Do you mean acorns with possible weevils would be ok to use, or they did not have any weevils? I have wanted to do something like this for awhile, but every acorn I inspect here in Louisiana seems to have weevils.

The Mad Fermentationist (Mike) said...

That there hadn't been any acorns with weevil larva that they'd collected in Illinois.

I suspect the squirrels are smart enough to gather the best acorns around me. I had the best luck on windy days when I was getting them as they fell.

kevinlmcmahon said...

What would be the impact of including a little weevil in the brew?

The Mad Fermentationist (Mike) said...

The weevil itself might not be bad, but the hole and life-cycle could cause mold and other issues that could ruin the jar.

Anonymous said...

It's so sad to see an old tree go. Did you count the rings? Did you save any of the wood for oaking beer? I think it would be kind of neat to use the wood for browning malt over an open fire, too.

If you were incredibly ambitious, you could have used it as an excuse to learn coopering....

The Mad Fermentationist (Mike) said...

I wasn't there when they ground the stump, so no final count on the age. We've got a few of the bigger sections of the trunk though, which will give us something. I've been splitting the chunks (video) left behind for firewood, I'm sure a little will find its way into a beer eventually (once it is seasoned). Home smoked malt is something I've done (recipe), but hadn't thought of it with the oak!

Not even I'm mad enough to try coopering, my carpentry skills are non-existent as is!

Anonymous said...

relevant for your weevil issues:

Warren's Beer Adventures said...

I remember chewing on acorns (once) as a kid. The tannic flavor was overpowering. It is good to see you have found a use for the fruits of that old oak at the end of its life.

John H said...

I gotta have that glass! Where'd you find it?

The Mad Fermentationist (Mike) said...

It's one of my favorites. I bought it at Cristal Blumenau is southern Brazil... it's a thistle glass, classic for Scottish ales.

DMP said...

Did you sterilise the acorns at all or just dump them in and hope the intended microbes out compete anything nasty?

The Mad Fermentationist (Mike) said...

Just dumped them in. Generally a late-stage sour beer is pretty immune to unwanted microbes given the alcohol, acid, and low-oxygen. I also kegged this one so it was cold pretty soon after the acorns were added.

C. said...

Did you ever taste the acorns before adding them to the beer? I've had a couple of jars of foraged acorns aging away for about a year in preparation of adding them to a brew, but when I tasted one it was so tannic, I have my doubts about how long they can be in there before turning the whole batch inedibly bitter

The Mad Fermentationist (Mike) said...

I didn't taste them, just smelled. Didn't have any issues with excessive tannins in the finished beer. Maybe most of them just aren't extracted? You could leave them in larger pieces, but even chopped up in a food processor for a scaled-up batch I didn't have issues.

Unknown said...

I collected a bunch of acorns planning on fermenting them, but after leaving them to dry overnight a bunch of them started to sprout. Are these still useable? Or do they need to be completely whole?

The Mad Fermentationist (Mike) said...

I wouldn't... next time I'd store them somewhere cooler and drier!