I had made some lemonade for a party and now having some leftovers sitting on a counter for a few days it has started to ferment. The containers were all sterilized with bleach, produce was washed and water was boiled. It tastes totally fine. Would this be safe?

5 gallon water 1 c honey 1 c sugar 2 c fresh lemon juice 3 c barley Lemon zest Mint leaves

Add barley and honey/sugar to water, boil for 10 min Remove barley Steep lemon zest and mint leaves in the lemonade Once cooled down, add lemon juice

  • 1
    I'm afraid the conservative answer is likely that no, it isn't safe. However, it could be helpful to know 1) what sign do you have that it's fermented? And 2) did it have easy access to oxygen? (was it sitting in a pitcher with one of those twist-pour lids for example, or a tightly-lidded container?) I also wonder if the people at the homebrew se might know something more useful.
    – kitukwfyer
    Feb 18, 2020 at 23:50
  • @kitukwfyer note that on our site, we don't take subjective answers on food safety, and only apply official rules. So what you are calling the "conservative answer" is the only one that would be in scope. So the other information you are requesting is not relevant.
    – rumtscho
    Feb 19, 2020 at 11:13

2 Answers 2


Accidental fermentation is never safe. You have bacteria growing in your food, and you don't know which bacteria they are. Fermentation is only safe if you use a process which has been tested to only allow the growth of benign bacteria.

The containers were all sterilized with bleach, produce was washed and water was boiled

This is irrelevant. It is only good to ensure that you won't be starting with an unusually high load of random bacteria - because if you had such a contamination, the food could start spoiling before its usual storage lifetime has been reached. But once you either 1) reach the end of the storage lifetime (which is 4 hours on the counter, as for any prepared food) or have visible signs of spoiling (and fermentation is one of them), hygiene precautions stop mattering and your food is unsafe.


If you want to consume fruit juice after several days:

  1. the more it tastes fermented, the more likely it will give you indegestion/gas/the runs.
  2. the more it is carbonated / bubbly from fermentation, the more it can cause indegestion.
  3. if you boil it or put alcohol in it, it will be a bit safer, but it can still cause indegestion.
  4. the fruit substrate bacteria aren't notably beneficial especially in volume.
  5. having a sip is not very noxious unless you have a weak constitution.

Having a small amount of natural fermentation of non-sugary vegetables or couscous provides the digestive system with beneficial bacteria the digest veg and carb inside you, but sugary food bacteria are not metabolically stable in teh gut except for special fermentation granules like fruit kefir... which can make naturally bubble lemonade, unfortunately, if you drink too much fruit kefir, then your entire gut carbonates too much and causes gas issues.

Fermented food varies depending on the pH and substrate. For example, lactose has evolved in animals because it could not be digested by all the microbes that could previously digest glucose/galactose which is found in plants. So milk is often used as a substrate for biological cultures which are fairly symbiotic with humans.

Fruit is normally subject to funghi and microbiota that are not particularly dangerous to humans like meat is, because they don't particularly thrive in the human body, but they can give you indegestion and the runs/dysentery.

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