Cold Crashing Explained

I wrote a blog about how beer makers don’t know how to make cider. In it, I said that they add sugar when they shouldn’t unless they are trying to make wine, rush the cider instead of letting it age, and they believe they can cold crash cider to stop fermentation to have a naturally sweet cider without chemicals.

Because I knew that UK craft cider makers allow their cider to ferment outdoors, which allows their cider to freeze, yet it will start fermenting again when it thaws, I said that cold crashing cider is impossible, but I didn’t know why. I asked the Cider Workshop, and Jim K responded to me. He explained that cold crashing doesn’t kill yeast cells, contrary to home beer making beliefs, but just makes them go dormant, just like in cider making. However, the sugars in beer are not completely ferementable as they are in cider, so the yeast has a much harder time recovering from being dormant. He believes that the yeast could become active in beer eventually after a few months, but because beer makers rush things so much, chances are the beer is consumed before the yeast can be active again.

Jim also added that most good brewers use cold crashing as a way to clear the beer, much like how I use pectic enzymes, but that otherwise mash temperatures are used to control sweetness.

However, I have since been schooled by a beer maker, CvilleKevin. It turns out that I did not know the proper technique of cold crashing. He said, “Cold crashing is not the same as cooling. Chilling will make the yeast go dormant. Most types of yeast will drop to the bottom at that point. To cold crash you rack, cool, and rack again. Keep an eye on for a week or two to make sure you got it, or else you can go straight to a keg at that point.”

He continued, “By cold crashing, you are getting the yeast and nutrients to drop out of suspension and racking them out. You can do it with just about any yeast, but some are easier than others. Nottingham is very easy. One of its properties is that it flocculates at low temps and makes a nice compact sediment. Most ale and wheat yeasts are easy to crash. Wild yeast, lager yeast, champagne yeast and some wine yeasts are tougher.”

“I've been cold crashing cider for years without problems. I've got about 20 liters right now from last season that have been stored at room temp for over a year with no problems.”

When presented back to the Cider Workshop, Andrew Lea of Craft Cider Making further explained that in this context, it is not the cold temperatures that cause it to work, but instead the allowed “repeated rackings, thereby reducing yeast and nutrient to levels at which refermentation is less likely. So it fits into that hierarchy, and there are no guarantees!”

Since asking these questions, I found Ben Watson had addressed “cold shocking” in his Cider: Hard and Sweet book on page 166. The process is as CvilleKevin described it, adding after racking that “The cider should remain at a cold temperature, and then, before bottling, you’ll need to add potassium sorbate… to guard against refermentation… All this effort strikes me as way too much of a hassle for the amateur cidermaker… A much more practical solution, and one that doesn’t involve preservatives, is to stabilize the cider after bottling by pasteurizing it, bottle and all.”

Therefore, after much research and asking of question, I now believe that “cold crashing” can be done on cider as long as racking is done with the reduced temperatures with the use of potassium metasulfite and potassium sorbate to ensure that the cider would not start fermenting again.

Making a sweet or dry wine or cider

I have eluded to the fact that it is much easier to make a dry wine or cider than it is to make a sweet one. I think it is time to go a little deeper into the topic.

The yeast in cider and wine eat sugar, turning it into alcohol. Thing is, they will do that until one of two things happens. The first one is that the yeast run out of sugar. At this point, it is a dry beverage with no sweetness, which some may dislike. This process is the easiest to accomplish because it allows the yeast to do what it wants to do. To obtain a sweet wine or cider, one must interfere with the batch, either killing the yeast prematurely before all the sugar is gone, or making sure the yeast is truly dead before adding more sugar back. I will explore those options in the posts to come.

How do you know if the wine or cider is sweet or dry? The answer is as simple as taking a specific gravity reading taken with a hydrometer. That reading can be classified into the corresponding sweetness:

• 1.025 Very Sweet
• 1.020 Sweet
• 1.015 Medium Sweet
• 1.010 Medium Dry
• 1.005 Dry

It is not really recommended bottling much higher than 1.025, as most people would not find it very drinkable. Also, if the yeast starts fermenting again, the carbon dioxide released could create too much pressure on the bottle, causing it to pop the cork, or worse yet, explode. Ben Watson in his Cider: Hard and Sweet cautions against bottling cider higher than 1.005 if it has not been stabilized, that is, if chemicals or pasteurization has not happened to ensure the yeast will not start fermenting again.

Air is the enemy

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.