Jumpin' Jack Flash, It's the Gas, Gas, Gas

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Tiny bubbles, in the wine . . . 

Damn! and just when I was starting to get it.

-- Edward Degas, on his deathbed. Degas, despite his cool name, did not make wine, but rather art. 

Degassing can be a contentious subject for people making their first wine from kits. It's crucial for the success of the kit to get all of the fizz out of it, not only because many wines taste weird when they're unintentionally fizzy, but also because the fining agents don't work correctly in the presence of CO2 bubbles. 

Tickle tickle

Where Does CO2 Come From?

The CO2  bubbles are in the wine from yeast activity. Yeast only turns about half of the sugar in your wine into delicious alcohol. A smaller percentage goes into various chemical compounds, but the majority of the rest of it gets turned into carbon dioxide. Initially the CO2 is in a form too fine to be detected, but after a while the wine will saturate and begin to form bubbles of gas that will float to the surface and burst. As long as the yeast is working, there will be gas going into the wine, more-or-less balanced by gas bubbles coming out. 

That's pretty active . . . 

However, after fermentation stops in 10-15 days (for most kits) the CO2 doesn't suddenly disappear. The wine is still saturated and slowly out-gassing on its own. In order to make the schedule of clearing and bottling work, it's necessary to stir the wine strongly enough to drive off the rest of the gas. While it should be an easy and natural step, sometimes winemakers stir and stir, but despair of getting all of the gas out of their wine. 

What Influences Degassing

There are two reasons for the issues some people have with fizziness. First, because of the very short fermentation and clearing cycles, kit wines can still be quite fizzy, despite the fact that they've finished fermentation. 

The second, and more important factor is the temperature of the wine, both at the time the yeast is pitched, and the temperature it has been fermented and stored at all throughout the process. If the juice is too cold when the yeast is added it will take a long time for the fermentation to start. This ensures that the yeast will be playing catchup on eating all of the sugar and will still be trying to finish when you're ready to fine and stabilize. If they're still working, they're still making CO2 and you're not going to be able to get rid of it all. 

When you have the juice at the right temperature you not only ensure the yeast get going quickly and finish on time, you also give the wine time to, uh, expel gas on its own. Let me explain. 

When the yeast finally stop putting out carbon dioxide, the wine does not stop fizzing immediately. This is because the wine will outgas on its own. Just like a glass of soda left on a counter overnight, it will slowly become less fizzy, making your job easier. 


And that's not all! Getting the juice into the right temperature range (warm--read your instructions for the exact degrees) and keeping it there also ensures that it will outgas much more quickly than cold wine. Again, think of soda, this time two cans. Keep one ice cold and warm the other one up to 80 degrees F, and then open both at the same time. The ice-cold can will hiss briefly, but will retain all of the crisp little bubbles of gas. The warm can, on the other hand, will burst forth in a mighty geyser of torrenting soda, and when you finally get to the liquid, it will be relatively flat and sad. This is because cold liquids absorb more CO2 than warm ones. Warm wine will hold less gas, again, making your life easier when you need to degas. 

Agitating and Cavitating

Once the temperature is squared away, the thing that continues to bring confusion is the idea that the wine must be stirred to degas it. On the surface, simple enough, but the wording is completely misleading. You don't actually stir the wine at all: you agitate it. 

That's because stirring will simply move the wine around in the carboy, causing it to circle around uselessly, without driving off any gas. The true action is to move your stirring implement through the wine fast enough that it causes  Cavitation

kavəˈtāSHən noun

The formation of an empty space within a solid object or body. the formation of bubbles in a liquid, typically by the movement of a propeller through it.

The drag of the tip of the stirring implement creates a zone of low pressure behind it so strong that it causes a void (which looks like a bubble, but really isn't a bubble at all) in the liquid. Because this bubble has extremely low pressure, it implodes almost instantly. This implosion creates a immense shock wave, and it's this shock wave that knocks the bubbles out of suspension. 

The Physics of Cavitation

Those bubbles on the edge of the propellor are not air: they're voids that contain a small amount of vapor

Cavitation is a problem in some areas of engineering. People who design boat propellors have to engineer them very carefully: if they have too much drag, or if the prop spins up too rapidly, it can cause tip vortex cavitation, which can bend or even break the propeller. 

Beautifully murderous

Another fascinating place where cavitation is found is in the work of the Mantis shrimp. These charming little stomatopods are pound for pound the ultimate murder machines of the ocean, referred to variously as 'sea locusts', 'prawn killers', and, ''thumb splitters', because of their incredible ability to annihilate anything around them. They throw a punch with their claws that accelerates with the force of over 10,000 gravities. To put that into perspective, if you could move your arm that fast, you could throw a golf ball into the asteroid belt. 

In fact their punch is so potent that if the initial blow doesn't instantly kill their prey, or blow it's limbs off in all directions, the subsequent cavitation bubble collapse will pulverise them anyway. The blow is so strong that Mantis shrimp aren't easy to keep in captivity. Not only will they kill anything they find, they can also punch holes into a glass or plexi tank and shatter it completely. 

How to Stir Effectively

If you're not a Mantis shrimp, but want to degas your wine, what are your options? Most directions mention a spoon, which does work, but requires stirring effort well beyond what you might expect.

Ain't gonna stir itself, Tim

To quote my colleague Tim Patterson, rest his soul,

"After racking again to a clean new carboy I am now [degassing] the wine in an attempt to remove unwanted CO2 gas. It's a fairly miserable process of stirring like a madman for several minutes, over and over, until this foamy head is no more."

Some folks swear by a vacuum pump. I mainly swear at them. Vacuum pumps can remove gas, but they have some inherent problems. First, one sufficient to raise 25+ inches of mercury (a measure of vacuum efficiency) are expensive. Second, even if you get one used (mine came from a mortuary) you can't use them on plastic or metal carboys (they crumple like tinfoil), and there is a non-zero possibility that your glass carboy will implode like a bomb when you turn it on. 

I am not a fan. 

By far the best solution is to use a drill-mounted stirring whip. These come in a variety of types, some with little swivelling paddles, and some with plastic strings on the end like a Weed-Whip. But the very best one is the  Three Prong Degasser

Looks like a rocket, works like the bomb

Constructed of bonded high density polyethylene plastic, its design is superior to other drill-mounted stirring rods because when you use it at full speed, the tips cause incredible cavitation in your wine. And I do mean, at full speed.

The stirring action is incredible, and your shoulders and elbows will thank you for taking pity on them. 

Things to Keep In Mind

Always start slowly . . .

  1. Always do a 'test' stir before going full speed, or you may get a gusher.
  2. Use an AC drill rather than a battery model, unless you've got a contractor-grade drill. Modest home drills run out of juice or are too wimpy for full-on stirring
  3. Clean and sanitise your degasser, but never store it in sulfite solution: the food-grade plastic will become brittle and snap. 
  4. You should be able to completely degas a wine that's been through processing at the right temperature in less than three minutes by going back-and-forth (see below).
  5. If it takes longer than three minutes, you've got a problem: either the wine is too cold, never finished fermentation, or you're actually finished, and mistaking foam for fizz. 

Degassing is a simple process that should be easy, and with a good drill-mounted whip, it can be. If you'd like to see a full-on degassing session, check out the video below.

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