When people ask if their hard cider can go bad, they are often worried that it might spoil or turn into something that would make them ill. Usually, the cider in question is often sitting in a bucket and has a crust of white or even a moldy film or layer on top of it. Sometimes, it is in a glass container but only half filled. It looks like it is bad and maybe even something that could make you ill, but the reality is usually very different. Cider is usually rather acidic and has alcohol in it. Therefore, the simple answer to the question is “no”, hard cider cannot go bad. But, as usual, we need to unpack that simple answer a bit.
Yeast creates cider by processing the sugar found in the juice. It converts this sugar into ethanol and CO2 and that combined with the acidic characteristics of apple juice means cider doesn’t spoil. At least it doesn’t spoil like meat, cheese, or even an apple might spoil. That is because the ethanol that the yeast creates is a antimicrobial and antibacterial compound. It inhibits the growth of many organisms, especially those that can make humans ill. Once cider hits a level of around 2.5% alcohol by volume, it can effectively kill most human pathogens in hours(1). Given apples are usually acidic with a pH from 3.0-4.0. This acid weakens the cell walls of organisms and makes them more susceptible to damage from antimicrobial agents. Acids make ethanol an even more effective antimicrobial compound. Ethanol is usually what limits yeast fermentation as most yeast struggle to survive above 18% ABV. Given your cider is acidic and has ethanol, it can’t really spoil. But, it can evolve.
Cider is created in an anaerobic system or at least the most desirable ciders are. The lack of oxygen forces yeast to use a less efficient pathway to create energy and reproduce. Yeast prefer to use a respiration process where oxygen is readily available to process sugar and create energy. By removing oxygen, we force the yeast to use a different pathway. This is the fermentation pathway that creates ethanol and CO2. CO2 can also have antimicrobial characteristics but ethanol tends to be the greater antimicrobial agent. However, ethanol can be broken down further, especially if it becomes exposed to oxygen. This is how vinegar is formed. Acetic acid bacteria uses the ethanol in cider and oxidizes it to create acetic acid. That means your cider can’t spoil but, it can become something else, which is vinegar. Other organisms, like film yeast can also grow on top of your cider and, this can even create a substrate for mold to grow but, the cider sitting below that film or crust is still cider. You may note that I said it’s still cider. I didn’t say it was good cider but, it’s also not bad or spoilt cider. It may be a cider with more acetic acid or aromatic compounds that you don’t enjoy, it may even have mycotoxins from mold, but fundamentally, it’s still cider.
Cider can’t go bad or spoil. It can only evolve and become vinegar and, to do that, it must have access to a lot of oxygen. The good thing is that even if your cider evolved into vinegar, you would still have a useful produce since apple cider vinegar is a great tool for preserving vegetables and making salad dressings. That is because vinegar doesn’t spoil either. When making cider, the worse thing that can happen is you end up with vinegar, which doesn’t really leave you in pickle (or maybe it does).
(1) Menz, G., Alfred, P., and Vriesekoop, F. 2011. Growth and Survival of Foodborne Pathogens in Beer. J. Food Prot. 74:1670-1675.
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