A common question I get from new cider maker’s about making sweet or semi-sweet cider is “how do I stop fermentation of my cider?” This question is generally asked for two reasons. The first is to stop active fermentation early to keep a cider sweet before it ferments all the way dry. The second is to stop future fermentation so the cider can be back sweetened without the chance of refermentation.
This seemingly simple question is more difficult than one would expect and requires some additional information to answer. See, to stop fermentation of cider, the yeast needs to removed from the cider, inhibited and or killed.
The first scenario, stopping active fermentation, is difficult because a robust active yeast can be hard to kill with anything that is safe to drink. Filtering can be a possible solution but for the home cider maker, it is probably out of reach.
This leads to the second scenario, and preferred method, where the cider is fermented dry and then back sweetened. This method achieves the same back sweeten taste, without the hassle of trying to halt active fermentation.
One additional method for stopping fermentation to achieve a naturally sweet hard cider can be achieved by using a technique called keeving. A keeved cider is when the juice becomes nutrient deficient and fermentation naturally stalls, usually due to a lack of nitrogen. The traditional technique often used in French cider making is fascinating but will definitely require an article of its own!
How to stop fermentation to back sweeten hard cider:
While stopping active fermentation is difficult, especially for the home cider maker, it is easy to inhibit future fermentation of cider once the yeast has become inactive. By inactive, I mean that the yeast has eaten all of the available sugars such as when the cider has been fermented to dry. At this point, the yeast become inactive since they do not have a food source.
At this point, future fermentation can be inhibited by using a mix of campden and potassium sorbate to stabilize the hard cider. This method is common practice in the wine industry for making sweet wine and increasingly popular in commercial cider making.
Steps to kill yeast in cider:
- Cold crash the cider
- Rack the cider
- Add Campden tablets
- Add Potassium Sorbate
Cold crash the hard cider
The first step to this process is to thoroughly cold crash the cider for a couple of days. This will allow a large portion of the yeast to settle to the bottom which can then be racked without transferring large amounts of yeast. Minimizing the amount of yeast in the hard cider will make it easier to stabilize
With the bulk of the yeast removed, the next step is to use Campden and Sorbates to manage the remaining yeast.
Stabilizing cider with campden and potassium sorbate:
Adding campden and sorbate to cider together is an effective way to stop any further fermentation when back sweetening with a fermentable sugar. While many suggest both will work independently, the use of both will diminish yeast activity through attrition more effectively together.
A common misconception is that campden, AKA potassium metabisulfite, will kill the yeast. This is not totally true. Campden releases sulfites, or SO2, into the cider which stuns and weakens the yeast. The campden may kill off some weaker yeast but mainly puts them into dormancy. Once the sulfites naturally work their way out of the cider, there may be a few live yeast cells capable of reproducing. This is where the potassium sorbate comes in.
Potassium sorbate is a common preservative that renders yeast incapable of reproducing. Like campden, sorbate will not kill actively fermenting yeast, but once any surviving yeast dies off, the cider will be free of living yeast. Potassium sorbate will also protect the hard cider from oxidation and preserve the freshness.
How much campden and sorbate to add?
I follow the manufacturer’s recommendations that are found on the package. I generally use LD Carlson and they suggest the following:
Campden: 1 tablet per gallon
Potassium Sorbate: ½ tsp. per gallon