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.

Back Sweetening

Let’s say that you weren’t monitoring the wine or cider batch and the yeast ate all the sugar until the yeast died and the batch tastes dry, but you wanted it sweet. The solution to the problem is called back sweetening.

First off, the yeast should be verified as dead, which can be done by adding potassium sorbate or pasteurizing. From there, sugar or juice can be added to make it sweet. This technique is used with making ciders flavored with other fruits.

In his book Craft Cider Making, Andrew Lea talks about making sweet ciders, “If you want to sweeten dry ciders with added sugar (or with frozen or concentrated apple juice) but you do not want to pasteurise or filter them, it is important that they should be racked and stored for several months after fermentation is complete, to allow the yeast to die out completely before the sugar is added. Otherwise the risk of re-fermentation is considerable. The chances of re-fermentation can be reduced by the addition of yeast inhibitors such as potassium sorbate and benzoate at levels up to 200 ppm. (Both these materials occur naturally in rowan berries and cranberries respectively). Potassium sorbate may be bought from home winemaking suppliers. It is most effective if combined with say 50 ppm of SO2 added at the same time. If the cider is to be sold, however, a total of 200 ppm for the sum of sulphite and sorbate must not be exceeded."

I should note that you do not need to add potassium sorbate to a dry wine or cider if you decide to back sweeten with an artificial sweeteners such as sucralose (Splenda). Most artificial sweeteners are not edible by yeast, so there is no risk that fermentation will start up again. However, using artificial sweeteners is sometimes frowned upon as not being natural, affecting the texture of the cider or wine, causing the wine or cider to have an aftertaste and off flavors, and some even claim it gives them headaches to consume such a product, so consider these issues before deciding to use artificial sweeteners.

Kill the Yeast

In my last post, I said in order to obtain a sweet cider, the yeast needs to be killed to prevent it from eating any more sugar. There are several ways to do this, including the use of potassium sorbate or pasteurizing.

I have stressed that when picking out sources to make wine and cider from that it needs to be preservative free because the preservatives will prevent the yeast from fermenting. Now, when the yeast is towards the end of fermentation, preservatives in the form of potassium sorbate help kill the yeast to stop fermentation. [Edit: Potassium sorbate does not kill yeast. It prevents it from multiplying. Therefore, when fermentation is done and there is no sugar left, potassium sorbate blocks the dieing yeast from eating at any new sugar added.]

If you don’t want to add chemicals, the other option to kill the yeast is by pasteurizing. Andrew Lea describes the process as follows: “The sweetened bottled cider can then be batch pasteurised on a domestic scale in tanks of hot water e.g. at 68^o C for 20 minutes, although it is much more efficient to use a proper flow-through heat exchanger operating at 90^o C with a residence time of 30 seconds so that the pasteurised cider is filled directly into warmed bottles. Equipment of this sort does not come cheap and can usually only be justified in the context of a commercial operation.”

In Cider: Hard and Sweet, Ben Watson recommends having a mixture that reads 1.010 on a hydrometer, bottling it, and then possibly waiting a few days before pasteurizing. With “a large kettle on the stovetop, or in a metal tub or livestock trough that’s set over a propane burner outdoors, place the capped bottles in the water bath; the water should come up to the fill line on the necks. Fill one bottle with water that’s at about the same temperature or cooler than the cider, and leave it uncapped, with a thermometer inserted into it. Heat the water in the tub or kettle until the thermometer in the test bottle reads 150⁰F (65⁰C) for 10 to 20 minutes… The bottles may start leaking gas around their caps and hissing; this is fine and isn’t cause for concern. Remove the bottles carefully and cool them slowly to minimize any risk of breakage.”