Why would I want to do this? For one, my wife loves the taste of beer, but not the aftereffects of having a couple. That left her drinking the limited array of NA beers that you can get in my neck of the woods. Plus, she's a fan of darker beer styles that aren't exactly well represented in the NA beer landscape.
In addition, low ABV also means you can have a few without getting loopy. If I'm working outside in the garden, I want to plow the fields, not get plowed in the fields.
I've tried both the small grain bill and the boil off techniques. Neither of them produced what I would call good beer. Small grain bills produced thin, beer flavored water. Boiling left behind an aftertaste that's most generously described as different, but more accurately described as chemical.
That took me to cold mashing.
Rather than dive into why and how a cold mash works, let's get straight to the process.
I think of a cold mash as being the beer equivalent of making cold brew coffee. All you're really doing is mashing milled grains in cold water instead of hot water. The rest is pretty much the same as brewing the traditional way.
That said, cold mashing does have quirks.
First, you need a refrigerator to mash in, as well as some patience. This is because unless you have a way to constantly stir the mash for an hour in a near freezing room, a cold mash needs around eight hours to extract sugars.
For my beers, I use a variation on the Brew in a Bag (BIAB) brewing method. I line my three gallon brew pot with a mesh bag, add the grains to cold water, stir well, and stick the mash in a 37F(3C) refrigerator over night. When the mash is ready in the morning, I pull the grain bag, let it drain, and then transfer the wort to my eight gallon pot. From there, I use a BIAB calculator to determine how much water to add to the pot to reach my preboil volume.
In an ideal world, I'd use my eight gallon pot for the whole process to avoid adding water after the mash. Unfortunately, that pot won't fit in my fridge. Perhaps one day, a fridge I don't have to share with the rest of the family will appear. Until that day, I'll keep doing what I have to do.
Once the boil starts, the rest of the process will feel like any other brew day, until you check your starting gravity. That's where the result of cold mashing becomes obvious.
With a traditional mash schedule, I get around 75% efficiency. Cold mashing is more like 35%. That means what would have been a 1.046 wort for a lovely Pils is now 1.022. Depending upon what yeast you use (I lean towards those with lower attenuation, such as White Labs WLP002 and WLP820), the resulting ABV will be right around 2%.
For my beers, I usually go even lower.
An English Mild can have a starting gravity of 1.030. In cold mash terms, that's around 1.014. Throw in a yeast that attenuates at around 68% (The strains I use rarely hit above 70%), and the resulting beer has a robust 1.25% ABV.
With most of my brews, I'm getting right at, or slightly above that number. On a couple of occasions, I got as low as 1%, which qualifies as NA in some states. For me, that's perfect for that warm Summer day in the yard.
Before you take an existing recipe and go straight to a cold mash, we need to discuss taste and body.
After quite bit of experimenting, I've discovered a few truths. First, if you don't drop your bittering hops by roughly 1/3, the resulting beer will be far more bitter than your IBU calculator says it will. Second, due to the low residual dextrin content from the cold mash, the wort you're creating will not be as sweet as its traditional counterpart. Third, beers with low ABVs have thinner bodies that should be compensated for.
To get some of that sweetness back, I've found a few tricks.
Using lighter crystal malts, as well as more of them, makes a big difference. In the past, I rarely used crystal malts in the 10-20 Lovibond range (CaraHell and Red, Caramel 10L and 20L, etc.). Now, I use them in almost every batch.
Sweeter base malts also help. Thankfully, Pilsner malts are already on the sweeter side. I've also found that Golden Promise works great as well. In addition, Briess has a dehusked Pilsen malt called MaltGems that's milled to reduce bitter and astringent flavors. I have a batch brewing with it that will hopefully provide a proper comparison against standard Pilsner malt.
To give your beer a little body, wheat and oats are your friends. Beers with these low ABVs tend to have a thin mouthfeel. Using wheat (malted, flaked or torrified) or flaked oats brings some of that back. In my case, an Oatmeal Stout and a Dunkelweizen I brewed had much more substantial mouthfeels than my all barley efforts. With that knowledge, I've started adding 5-10% wheat or oats to most every beer.
Darker roasted malts, oddly enough, seem to like a cold mash. While they don't impart as much roast character, they're also less likely to add astringency. One of my best cold mash beers was actually a Stout that contained a fair amount of both Chocolate Malt and Roasted Barley.
For some Cold Mash beers you can brew, come back for Part 2.
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