Going Wild – Coolshipped Beers in the Home Brewery

This article on brewing coolship beers first appeared earlier over at the Canadian Homebewers Association – Canada’s equivalent of the AHA. This article takes a deep-dive into how to collect and brew with wild yeasts using a coolship approach.

I am re-posting this article below for those who are interested, although I encourage you to check out the original over at the CHA. And while you’re there, if you are a Canadian homebrewer, why not join the CHA and help them in their mission to promote the hobby of homebrewing in the great white north.

Hot scotchy’s are essential because these beers are brewed when its cool.

In October I posted an article on how to capture and brew with yeast isolated from your environment. This method allows you to produce a “house” yeast culture unique to your brewery. However, it is also a complex and time-consuming process that deviates from traditional, time-tested wild-brewing methods. In this article I’m going to describe a method similar to that used for traditional sour beer production, which can easily be used by any homebrewer to create Belgian-inspired but uniquely Canadian wild beers.

This process mimics parts of the traditional Belgian method but makes use of modern brewing techniques to simplify the brewing process. This includes eliminating turbid mashing, which is difficult to do with many homebrew setups (you need to be equipped to decoction mash) and is unnecessary given the level of control we have with modern infusion mashing techniques.


Brewing wild beers by coolshipping is simple, but these beers take a long time (8-36 months) to ferment so you need to be planning months or even years ahead when starting a wild brewing program. Key to this long ageing is the use of a very hot mash; this will create a wort with lots of dextrans, which will feed the wild yeast and bacteria over the months and years of the fermentation. These beers are typically lightly hopped in order to avoid suppressing the sour activity of wild bacteria. You brew these beers much the same as any other beer, but rather than cooling them with a chiller, you simply leave the pot outside, uncovered, and allow nature to cool your beer. At the same time, yeast and bacteria in the air will fall into the beer, inoculating it and starting the ferment.

Sample Recipe & Brewing Process

Letting nature chill the beer

You can brew many styles of beer using this method – from traditional Belgian sours (e.g. lambic-inspired beers), to modern recipes such as black rosemary saisons flavoured with caramelised raisins deglazed in port. While many styles can be brewed, I would suggest a simple golden sour recipe for beginners. This is a great starting point for a brewer new to wild brewing as it produces a beer which is interesting on its own, but which also works well with fruit, with spices, and can be blended with other beers. This beer is minimally hopped (1.5 IBUs), which will ensure that your wild bacteria will sour the beer. The amount of hops can be increased in future recipes if your beer gets too tart, but be careful, as most wild bacteria cannot tolerate more than 5 IBU. Lastly, a very high mash temperature is used to provide dextrans for the long fermentation. You can also make this recipe with a traditional turbid mash, but this is an advanced and long process that I personally prefer to avoid. I use this recipe for many purposes – it is the basis of my Everybody in the Pool solera, where I dump all of the interesting sour/wild bottle dregs I find. But I also use this for fruited sours and as a base for blending with other beers.

There are a few other factors you need to consider other than a recipe when brewing wild beers. Weather is an important factor – you want the cooling period (usually overnight) to be cool; 12C or cooler, and without snow or rain in the forecast. Some wind is good as it’ll speed cooling and deliver more yeast, but it isn’t required. If brewing in weather below freezing it is a good idea to brew in the morning so that the beer can be brought in before night. That said, I’ve had a few batches freeze solid, only for the beer to start fermenting a few days after being thawed and transferred to a fermenter. Location also matters – you need to select a cooling location where there is a good chance of collecting wild yeast. Luckily, this is pretty much any place outdoors, but a location with trees or other plants nearby is preferred. Lastly, it is best to brew in the location where you plan on chilling the beer in order to avoid lugging a pot of near-boiling wort around.

Recipe – Everybody In The Pool Golden Sour

Coolshipping was successful.


  • 70% 2-row malt
  • 20% raw or flaked wheat
  • 5% aromatic malt
  • 5% flaked oats
  • 1.5 IBU low-alpha hops (I prefer noble varieties)

I typically aim for a starting gravity of 1.050 to 1.060. For a 20L batch at 75% efficiency, I use 3.5 kg of 2-row, 1 kg of raw red wheat, 0.3 kg of aromatic malt and 0.3kg of oats. The type of 2-row malt is not overly important – pilsner malt, conventional 2-row, or even pale ale malts such as Maris Otter can be used. For raw wheat I literally use the wheat we buy for animal feed – if you cannot find raw wheat, torrified or flaked wheat works equally well.


  1. Mash at 70 to 72C (158 – 162F) for 30 to 40 minutes
  2. Sparge with 78C water
  3. Bring collected wort to a boil and add hops
  4. After the boil, kill the heat. Remove any hop spiders, lids or other extraneous components from the pot, and leave the pot outside with the lid off until cooled.
  5. Transfer the beer to a clean, oxygen-impermeable fermenter equipped with an airlock. I would suggest a glass carboy with airlock over other types of fermenters. The fermenter should be as full as possible, as airspace can promote the formation of undesired flavours.
  6. Place the fermenter someplace out of the way with a temperature between 16C and 24C…and let it sit for a long time. Be sure to top-up the airlock frequently, to prevent it from going dry.


Fermentation started after 4 days.

Visible signs of fermentation can take as long as two weeks to appear, although 4 to 7 days is more common. Avoid the temptation to taste the wort in the first month – food poisoning bacteria can grow during the early stages of fermentation, but will die off after a few months of fermentation. If you are concerned, during the boil you can add 1.5 mL of 88% lactic acid for every 4L of wort. This will drop the pH of the beer below pH 4.5, which will suppress the growth of these organisms. I have covered the topic of infection risk during wild brewing and the microbiology of wild fermentation over a couple of articles on my blog if you have concerns or questions.

Fermentation of these beers is slow, taking months or even years to complete. Within a month the beer should form an odd looking pellicle – typically a layer of slimy or fuzzy looking bubbles and chunks. So long as this pellicle colour remains white, grey or tan, it is normal and should not be disturbed. If it starts to take on bolder colours – reds, greens, blacks, etc – you have a mould infection and the beer should be dumped. Your beer may also go through a period of “sickness”, where it becomes thick and viscous, sometimes with snot-like tendrils throughout the beer. As with the pellicle, this is completely normal and will go away with additional ageing. The breakup of the pellicle (assuming this occurred without you disturbing the beer) is often a sign that the beer is ready to package, although in my experience the beer will often maintain a pellicle long after it is ready to bottle.

I would recommend leaving the beer at least 8 months prior to sampling, with 12 to 18 months being more typical. These beers should not be packaged until the gravity of the beer holds steady for at least a month, and additional ageing after this point will help further develop the flavour and character of the beer. As a rule, the longer you age the beer the more sour and “funky” (earth, leather and other spice notes) the beer will become. It is critical to keep the airlock filled and to limit the opening of the fermenter throughout fermentation, as oxygen can allow formation of acetic acid (vinegar) and ethyl acetate (apples  and nail polish remover). In small amounts this can be pleasant, but this character can quickly become unpalatable. These beers are not necessarily done once ageing is complete. Fruit and spices can be added a month or so before packaging to add more flavour and character to the beer. If the beer is unbalanced – for example, is too sour – it can be blended with another sour or “clean” beer prior to packaging.

Before Packaging

A perfectly balanced wild beer, with a nice balance of acidity and funky yeast character, is rarely the outcome of this brewing process. Rather, the beers tend to be 1-dimensional – e.g. sour without funk. This is not a homebrewer-scale issue – indeed, the classical character of beers such as Gueze and lambic are a product of blending multiple batches of wild beer in order to get a desirable final product. As such, you should expect to need to do something to the beer prior to packaging it, in order to bring it into balance. Here are a few suggestions:

  1. Blend with other sour/wild beers. This is the traditional Belgian approach but requires that you maintain a fairly large stock of sour beers of varying ages for blending. This is not out of the reach of homebrewers, but does require that you dedicate the time and fermenters required to maintain a variety of sour beers stocks.
  2. If you keg your beer you can combine a sour beer with a clean beer – but you need to be careful as the wild yeast in the sour beer will ferment the sugars and dextrins left behind by commercial brewers yeasts, leading to over-carbonation, and if bottled, exploding bottles. These blends need to be kept cool to limit fermentation, and should be checked frequently to ensure that pressure is not building. Brew a beer to complement your wild beer. Saisons are a classical style to blend with a highly acidic sour beer – the resulting tart saisons are complex and refreshing. Overly funky beers that lack acidity can be blended with a kettle soured beer such as a Berliner Weisse to create something similar to a sour made by blending multiple wild beers together. Many other styles can be blended with a wild beer – for example, sour stouts are often made by blending a highly sour beer with a sweeter stout. If you want to bottle the beer or store it for any length of time, you may want to try pasteurizing the sour beer – this will allow it to be blended with a clean beer without the wild yeast creating bottle bombs.
  3. Add fruit. Fruit and wild beers go together well. Acidic fruits such as raspberries and sour cherries can add sourness and balance out excess funk, while softer fruits (peaches, plums) can take the edge off of an overly acidic beer. I prefer to add fruit a month or two prior to my planned packaging date. This gives enough time for the sugars in the fruit to ferment completely, while preserving the flavour and aroma of the fruit.
  4. Add spices. Like fruit, many spices work well with wild beers. Hibiscus can add fruitiness and a sweetness to highly sour beers. Coriander can add a citrus character as well as some funk-like notes. Cardamom, grains of paradise, juniper berries, ginger, black pepper, even spruce, can be added to add complexity and character.
  5. Add oak. Oak cubes, such as those used in winemaking, are a great way to add balance and mouthfeel to a wild beer. Oak can provide flavours which provide the sensation of sweetness and a fuller mouthfeel to a beer, which can help balance out an overly sour beer. Oak can also contribute flavours of vanilla, caramel, toast and wood to the beer – a nice complement to many of the flavours developed during a wild fermentation.
  6. Use a combination of the above. Wild beers are treasured for their complexity, and it is not uncommon to use multiple methods to achieve that goal.


Packaging wild beers can be troublesome. If packaged too early, the wild yeasts can continue to consume the dextrins, leading to over-carbonation and even exploding bottles. However, well-aged beers often lack the yeast needed to bottle-carbonate a beer, requiring a bottling strain be added. Wild beers are usually packaged with large volumes of CO2 – 3 to 6 volumes is typical (most clean beers range of 1.8 to 2.5 volumes CO2). If aiming for the higher end you need to purchase special bottles intended for these pressures – e.g. champagne bottles, or reused Belgian bottles. The prolonged ageing also leads to the loss of most of the dissolved COnormally present in beer. As such, special priming calculators need to be used, or you may end up with flat beer. I package in a variety of methods, but my preferred two options are:

  1. Keg and force carbonate. This eliminates the issues that come with trying to properly carbonate bottles. It is also more tolerant to beers packaged too early, as the colder temperatures of your keezer/kegorator will prevent additional fermentation. The downside to this method is that it is hard to pour beer kegged at 3+ volumes of CO2, meaning kegged sours are often served at lower pressure than is on-style.
  2. Force carbonate to a known low-level (1 to 1.5 volumes CO2) and bottle in campaign bottles, adding a small amount of rehydrated champagne yeast to each bottle to help with carbonation. I find this to be more reliable than using a sour-beer priming calculator – and it also makes it easy to put away half a batch in bottles for long-term ageing, and to then crank up the pressure in the keg  to carbonate the remainder for immediate enjoyment.

While the brewing time is lengthy, the beers produced by wild fermentations are unique and well worth the wait. And whether you brew one wild beer a year, or start a large scale wild program, these beers will be a welcomed addition to your beer cellar.

5 thoughts on “Going Wild – Coolshipped Beers in the Home Brewery

  • March 9, 2019 at 11:30 PM

    Hi there, this is really really useful, so thanks for posting. Just wondering what you think of doing this as a full-volume BIAB mash? Would you just mash for 30-40 mins at 70-72C, remove bag and then boil with hops, etc?

    • March 11, 2019 at 12:03 PM

      That is exactly what I would do – the mash temp and time are what are important, not the mash method. So a standard BIAB approach, but at the higher mash temp and shorter time, should work fine.

  • December 24, 2018 at 5:14 PM

    Nice article, but I need to address my safety concerns for adding strong acids directly to boiling water. This is dangerous because it can cause tremendous boil overs in a flash of a moment. It’s safer to add acids after boiling when the temperature has dropped well below boiling temperature.
    That said, it’s even more dangerous to add water directly to strong acids, because this releases a large amount of energy that can (and will) cause it to boil very violently!

    • December 26, 2018 at 7:02 PM

      This is a non-issue with the minute amounts of acid we are adding. Even at a full boil, the amount of additional heat generated by the dissolution of 4-8 ml of 88% lactic acid is insufficient to cause a localized increase in boiling/foaming. Lactic acid is not a strong acid, and the heat released when it is diluted in water is minimal (a few percent of what is released by strong acids such as HCl). I’ve done 40L batches where we add a full 15 ml of lactic acid during the boil without issue.

      If you’re worried, there is nothing wrong with adding it to the pre-boil wort. But it is a non-issue for the volumes of acid we are adding.


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