After my long series of articles about casks I have received a few messages from Cask lovers asking a few technical questions. I present them here in abridged form:
In your What’s Brewing article you recommend leaving at least 1L of headspace in your casks.
- What’s your favorite method for measuring that?
- Do you just eyeball it or do you have a tool to measure?
- Also, how do you find the headspace affects your ability to calculate predicted final C02 volumes?
- I was surprised when I did some research online and found lots of people saying not to leave any headspace when filling casks! Their reasoning seemed mostly to be because the headspace wasn’t “necessary” and it prevented them from accurately calculating C02 vol/L. I always thought that the headspace was crucial for the yeast to have enough oxygen during refermentation. Am I completely wrong?
My views aren’t really the accepted method. I find what works for me and what the customers seem to like, however I’m always happy to explain why I do what I do.
To fill a cask to the appropriate level I have a method where I sort of roll the filled cask a few degrees to see when beer will come out a little. I know that seems vague but I kind of eyeball it these days. I’ve had sanitised things to dip in but if it’s foamy it’s not clear and dipping anything in is risky business. This system means I usually “over” fill them then pour away the excess few ounces, a safer bet than trying to top up over and over which can also lead to infection (I’ve been very lucky over all). I know this seems counter intuitive but I honestly find this to be the best system. In the UK, underfilling casks was a serious offense as unscrupulous brewers could profit from it. That isn’t the same here, all of my casks are listed with the LDB as 19L and 39L. The other reason is that over here stillages tend to be built wrong – they are often pre-stooped so the casks are tapped at an angle, if beer is next to the shive hole the compressed gas will push it out. Permanent stillages should be perfectly level for venting, spiling, tapping and serving, only as the cask gets low should it be chocked up. If you tap it on a perfectly level stillage then a cask can be full to the top.
I genuinely don’t concern myself with target volumes either, I honestly think that madness lies for those who try to drill down the science on it. I’ve lost about 1% of my casks to popping and less than 1% have come out flat. I try to make sure that each cask is a little over-carbonated because I’ll be able to leave it cold stillaged and spiled to settle for a few days before serving. As long as the cask doesn’t get moved unnecessarily and is kept at fridge temp it’ll happily maintain a carbonation of around 1.4 ish for a week even without a breather – although I make sure my casks are blown through in a week max. CAMRA UK recommends real ale be served at 1.2 volumes (if I recall correctly) but would accept anything up to 1.7! I wouldn’t win many fans selling beer at 1.2! Pop and most kegged beer is commonly carbonated to around 2.6 – 3.0 volumes.
Once I’ve left the cask to condition at room temp there’s CO2 built up inside the headspace, moving the cask to the fridge causes more gas to absorb into the beer because of the chilling effect. Below are some of the factors that can affect CO2 volume calculations and the reasons I don’t try to work them out:
How attenuated is the beer? What’s exact plato of the beer? What am I priming it with? Is it pure? What blend of sugars does it contain? Did it mix well? What is the yeast count in each cask? Is it healthy? How much is dead? What type of yeast is in there? What generation? How long did you cold crash for? How flocculated was the yeast? Do I need to add fresh yeast? The same yeast? How much? Fruit? What types of fruit sugars are left, How does the yeast react to those sugars, Are there other yeasts? Is there enough oxygen to propagate healthy yeast? Do I need that or is a small amount enough? Do I need any? How much residual CO2 is left in the beer? Did you rumble it? How long for? At what pressure? At what temperature? Have there been any additions such as: dry hopping with pellets or leaf, flavourings, Do they have any sugar content? Lees from the fermenter? Proteins? Nucleation sites? Oils? Are there finings? What type? How much? Were they well mixed? Are they fresh? Do they react well with this yeast? How long will they take to clarify the beer and drop out the yeast? Will the cask be taken for walks? inverted? stillaged? how often? how long? What’s exact ambient temperature the cask will be stored at? for how long? how long in the fridge? Is it a pin? a firkin? a kilderkin? My head hurts.
Do you ever use fruit sugars from purees or juices to fully or partially prime your casks?
I tend to prime my firkins with 20ml invert sugar, 7-10ml vegan Biofine finings (Pins 10ml/5ml). After I fill them and clumsily roll them to the other side of the brewery floor I leave them keystone up overnight to warm up as labels don’t stick well on cold metal. The next day I put a label on the face and also a small label on the outer rim above the shive hole so that when stacked they can be identified from the side. Once labelled, I invert them so that the finings and lees travel the length of the cask and mix further. The next day I flip them back again for the same reason and then I start checking the keystones for signs of bulging.and leave them out of the fridge until I notice the bubbling of one of the keystones then I immediately move them all into the fridge. In the summer I have to be more vigilant because the higher ambient temperature can cause them to over carbonate and explode.
Priming with purees, juices and syrups is a very risky proposition because the different sugars in different fruit can ferment in different ways and you’ll often have to add so much to have flavour that there’ll be far too much sugar. I suggest when doing this that you transfer to a clean carboy add the puree etc then wait a day or 2 for those easy sugars to be eaten, then chill before racking to the cask. This is why I sometime use quality flavoured syrups or cocktail bitters, the flavour is strong and the sugar content is much more manageable. Juices are often too thin to have a noticeable effect, I find sometimes that adding juice “waters down” the beer significantly.
Watch for adding recently defrosted purees too, Let them get close to room temp if you can, it is like adding ice cubes and will affect the yeast – leave the cask for as long as possible to warm and condition. Similarly if the yeast is active dumping anything icy, sugary or acidic in may cause some immediate foaming.
There’s enough ambient oxygen when racking a cask for the yeast but I find they don’t really need it, a small amount of yeast will make more than enough CO2. The bonus is that the yeast will grab most available oxygen hopefully preventing the beer from becoming oxydised.
How long can a cask be kept before going flat? How do you clean a cask?
Once opened a cask can go flat in a few hours, if it is kept still and cold it’ll last several days, even a week or more, Temperature and stability are the keys. When one considers that CAMRA UK recommends a carbonation level of 1.2 in real ale it’s not difficult to retain some residual CO2. If a cask is sealed it will, theoretically, keep indefinitely.
Cleaning casks is a chore, they should be sealed or rinsed as soon as possible after use. Hop bags or any other item in the cask should be removed. They can be sealed using a tut and clip cork (a spile or tape can be used in a pinch) so they can be moved without making a mess. They can get pretty nasty if you don’t get to them quickly. Use a flash light or other source to illuminate the cask from the keystone end then look in the shive hole, if there’s still dried on lees then use a high pressure hose to move it the or leave it overnight filled with hot PBW (Oxyclean). When I’m ready to fill casks I fill a large tub with a hot caustic cleaner mix and then dip the whole cask, filling it – remember to wear industrial gloves and goggles! I leave it in the caustic a for a few minutes then let it drain back into the tub, after that I dip it into a light acid or sanitiser mix to remove the caustic, I give it a sani bath immediately prior to racking. I tend to do a dozen at once so I can get a little production line going and a workout deadlifting 50kg casks reusing the caustic and sanitizer as many times as possible.
If you have any other cask questions or anything else you can email me email@example.com or catch me at any of the good beer festivals!
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