Air is the enemy

December 17, 2009

Air is the ultimate enemy of cider, wine, and beer. More specifically, oxygen is the enemy of cider, wine, and beer. Every time a batch is made, all attempts to reduce the amount of air in the fermenting container, called headspace, is made.

Let me put it this way – if you bite into an apple, it starts to brown. This is called oxidization. If you put it down and don’t do anything with it, it might start to rot or mold. For that to happen, there needs to be little germs to eat the sugar and breathe oxygen. That is how a compost bin works, along with other bugs and critters to help the process along.

For brewing, I don’t want it to rot, I want it to ferment. Yeast needs sugar, but it does not need oxygen to work. I don’t need oxygen around my liquid, where, if there are any little germs in my liquid, it could allow them to breathe and ruin my drink. If that happens, it will smell and taste funny, or even turn to vinegar.

So after the brew is put into a container to ferment, with as little head space as possible, with the opening plugged. If everything goes right, the yeast will start to eat the sugar and convert it to alcohol and CO2. When the yeast first starts going to work, it releases CO2 so quickly that it can blow the plug out of the container, or it can even shatter glass due to the pressure build up. Instead, the plug is fitted with what is called an airlock or a blow off. There are two main kinds of airlocks, but both of them force the exiting air from the jug to pass though water and does not allow outside air, especially oxygen, back in. Actually, it is better to use cheap vodka instead of water in the airlocks for sanitization reasons. I had a batch that you could smell the juice on the escaping air, and it attracted fruit flies, and they managed to get into the air lock. I have heard stories of the pressure inside the fermenter dropping and sucking back the fluid in the airlock, so sucking back vodka that had killed the fruit flies and whatever nasty little germs they carried would be preferred to sucking back water with dead fruit flies and live nasty little germs they carried to ruin your batch, as having no oxygen present is not a guarantee that everything will be fine.

I mentioned a blow off. My husband’s first five gallon batch of beer started bubbling so fiercely that the little airlock could barely keep up. He had to remove the airlock and hook up a hose to the plug, and he stuck the other end in a pitcher of water with iodine, which is one of the sanitizers beer brewers use. It worked the same way as an airlock with the escaping gases passing though the water-iodine solution. In this case, he had to monitor it to make sure the pressure didn’t drop enough to suck the water-iodine solution back into his beer. Actually, after about two days, the yeast don’t have as much sugar since they have been eating it, and so the process begins to slow, at which point, the blow off can be removed and an airlock can be put in place again.

There is one other useful thing about CO2. Have you ever combined an acid like vinegar or lemon juice with baking soda? It has a chemical reaction and bubbles, releasing CO2. If you took a candle and placed it in a jar and then lit it, and then did this solution in another jar, you can “pour” the CO2 from the second jar into the first jar with the candle in it. The candle will “drown” in CO2 and go out because the CO2 displaces the oxygen the candle needs to burn. This shows that CO2 is a heaver gas than most air. It sinks, hence the reason it could be poured, and the reason it stayed in the jar to extinguish the candle. This is a good thing when I have to remove the plug from fermenting container to take a sample for measurements. It isn’t foolproof, but the CO2 should stay in the container near the liquid, and protecting it from the potential oxygen in the newly exposed air.

One last note about airlocks and air: I picked up from Andrew Lea was to put a little bit of food coloring in the air lock. This makes it easier to see the air passing through it. This is important because when there is no more sugar, the yeast die and fall to the bottom in what is called lees, so no more CO2 will be given off. If there is no more CO2 being given off, no more air will pass though the airlock, and it is time to move to the next step of the wine and cider making process.

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5 Responses to “Air is the enemy”


  1. […] all the nutrients, the other things don’t really have anything to eat to grow. It also serves to prevent oxidation, though it is not a cure all for either […]


  2. […] that my husband and I are a little twitchy about plastic because it allows plastic flavors and can breathe a bit, and glass doesn’t. I am comfortable using a plastic bucket for just a few weeks at the beginning […]


  3. […] then it inhales as I set it back down. This inhaling action causes it to suck on the contents of my airlock. Because the airlocks sometimes get some foam in them from the carboys, or even zealous fruit […]


  4. […] general section in the book discussing how to make wine. Interestingly, she does not mention that air will hurt wine, and barely talks about airlocks but does not stress their use, though she does mention sometimes […]


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