Barrel Ullagometer

Ullage!

What an interesting word!

It conjures up visions of exotic diseases – “My Kevin came back from a weekend on the Borneo Rivera with a big dose of the ullage”. Serve him right you may say! However, the real meaning is a little more mundane.

I noticed while typing “ullage” in my draft document that Microsot Word does not recognize this word in its spell-checker – it keeps trying to change it to “ululate” – which is close, but seems to have a totally different, if not more exciting, meaning relating to what happens when a beer goes bad.

I think the best explanation of the true meaning of the word “ullage” comes from the following poem by a very famous twentieth century Scottish poet.

 “My belly on the gantrees there,

The spigot frae my cullage

And wow but how the fizzin’ yill

In splilth increased the ullage!”

Excerpt from “A Drunk Man Looks at the Thistle”, Hugh MacDiarmid, 1892-1978

This was one of the very few poems containing the word “ullage” that I could find – so I’m very pleased about this as it brings additional excitement into an article that would be otherwise devoid of historical significance and culture.

Actually, this poem also clears up a small mystery about the Scottish accent. Many people, especially Americans, have a hard time understanding a traditional Scottish accent.  This poem clearly demonstrates that even if you could understand the accent, you still wouldn’t have a clue about what’s being said. If you have the time and inclination, there are on-line Scottish to English dictionaries that can help you to decode this poem. There are no English to Scottish Dictionaries for obvious reasons.

Now I’ve effectively insulted the entire Scottish nation and their esteemed poets, it’s perhaps time to return to the topic of this article.

Ullage is a term that comes from Latin and French. The following extract is taken from Wikipedia:

“The word comes ultimately from the Latin oculus, “eye”, which was used in a figurative sense by the Romans for the bung hole of a barrel. This was taken into French in the medievil period as oeil, from which a verb ouiller was created, to fill a barrel up to the bung hole. In turn, a noun ouillage was created, which was the immediate source of the word’s modern form, first recorded in Norman English about 1300, at first in the sense of the amount of liquid needed to fill a barrel up to the bung hole.”

As you can see, ullage is all about bung holes – something you probably knew anyway.

So, what have ullage and bung holes got to do with brewing beer?

Actually, ullage is simply the space (also known as headspace) above a liquid in a sealed vessel. Forget the bung holes – that was just the Romans and French having a good time (but not with each other).

In earlier times, the amount of ullage was used by tax collectors to determine how much beer was left in a barrel for taxation purposes and so having a lot of ullage was a very good situation to be in for the brewer – hence the advent of ullage-worship in Scotland.

So, why should we homebrewers even care about ullage? Although most beer containers, for example bottles and kegs, are made from impermeable materials like glass and stainless steel, others aren’t. One example is a bottle with a cork in it. Over a (very long) period of time, the level of liquid in a corked bottle may start to decrease. What’s happening is that liquid inside the bottle is able to permeate through the cork and become permanently lost. This may not be a problem in itself but, as the liquid passes in one direction, air surrounding the bottle can permeate through the cork in the other direction and enter the increasing headspace in the bottle. The beer becomes oxidized and can taste crap – that’s not a good situation. Monitoring the ullage space will indicate if this permeation is taking place. Next time you see a corked bottle of beer, mark the liquid level with a felt-tipped pen for future reference (this also helps to find out if others are drinking your beer).

There’s not much that can be done to resolve such issues with corked bottles. So why use corks in the first place? Note that not all types of beer are put in corked bottles. Those that are are normally very strong and often are dark beers or sour ales . Such beers can be improved by aging with a small amount of air being allowed to pass into it. Perhaps the best example would be an English barley wine. If you’ve ever drunk one of these that is a few years old, you’ll know exactly what I mean – rich smooth dried fruit vinous-sherry type flavors that taste so different from the beer when it was young. If you’ve never had an aged vintage English barley wine, make some and wait about two years – don’t forget to share it with your friends.

The other vessel in which ullage becomes a concern is a wooden barrel. These went out of fashion with ark (or were perhaps used to build it) but the recent craft beer revolution makes us strive to get that unique combination of flavors that nobody else on the planet can achieve. Re-enter the wooden barrel.

Because the wooden walls of a barrel are permeable and the surface area is relatively large (compared to a bottle cork) the potential for liquid loss and air ingress is high. This loss of booze is often expressed as the “Angels Share” – particularly by distillers of whiskey. As I mentioned above, certain beers will benefit from such an environment. However, a large amount of ullage through liquid loss invites more air into the barrel. Thus, there comes a point where the situation becomes intolerable and the barrel must be “topped up” with further beer to reduce this air before the beer turns into vinegar.

So, the question is how can we monitor the level of beer left in the barrel as the beer ages? Unlike a bottle, a wooden barrel is opaque and you can’t easily see into it.  Removing the bung to take a quick look allows air into the barrel anyway so the whole point of the exercise would be lost.

This project shows you how to make a very simple and cheap barrel ullage indicator. I’m going to call it the “ullagometer”.

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