Exact Answer: 7-14 days
Ideally, buttermilk is a type of milk that has been fermented. It can also be described as milk left after butter has been churned out fat from the cream. Buttermilk can be drunk directly and also used for cooking and baking purposes.
There are traditional and homemade ways of making buttermilk. Traditionally, this takes a longer period of leaving milk unrefrigerated in areas where it’s warmer. The second method is by use of lemon juice or vinegar. It is done by adding either a tablespoon of lemon juice or vinegar into a glass of milk; then, after 10 minutes, it becomes buttermilk.

How Long Does Buttermilk Last?
Buttermilk Type | Time Without Eating |
Refrigerated | 7 days |
Without Refrigerated | 14 days |
Frozen | 3 months |
Buttermilk lasts for a short period. It should be well stored at or below temperatures of 400C. It can last for a period of 7-14 days with or without being refrigerated. However, it can also be frozen up to 3 months. Freezing can be done by leaving some small space at the top of the container as buttermilk expands when it has frozen. Although freezing buttermilk alters with the texture and color of the buttermilk it still will be safe for cooking and baking purposes.
Once buttermilk has been opened, it can still be properly stored for future use. It should remain in its original container, refrigerated and tightly closed. One should not put the buttermilk container near the fridge door since temperature there are warm; rather, it should be stored in the main body of the refrigerator. This ensures that the buttermilk will not get spoiled in the shortest period.
Again, when buttermilk carton is exposed to daylight, it can easily interfere with its longevity. Once the carton has been left open for a period of 3 days or more, it releases watery substance at the top and the bottom of the container leaving high volume sediments with a fermented taste.
Reasons Why Buttermilk Lasts That Much Long?
Firstly, buttermilk has its own live bacteria. In the process of producing buttermilk, the bacteria consume the available lactose turning it to lactic acid. Therefore, due to acidity, high competition, and lack of food, it is difficult for buttermilk to get easily spoiled. The remaining good bacteria will be more functional by making the buttermilk thicker and sourer until all the available lactose gets finished.
Secondly, buttermilk can be either refrigerated at or below temperatures of 400C or frozen. If well refrigerated, it can last up to 7-14days; if it’s well frozen, it can last up to 3months. This is because it lacks butter, making it to last longer, unlike other dairy products that have longer longevity.
Furthermore, when buttermilk is in an unopened carton, it can stay longer as it is not exposed to direct heat compared to it being in an opened carton. Generally, open cartons will make the buttermilk loss its original flavor or taste.

Finally, practicing good hygiene while opening the carton can help its longevity. One’s fingers should be kept away from the lips of the carton, and drinking directly from the carton containing the buttermilk should be highly avoided once such habits can bring in yeast among other bacteria into the buttermilk causing it to spoil.
References
https://muse.jhu.edu/article/462403/summary

Sandeep Bhandari is the founder of ExactlyHowLong.com website.
I am a professional full-time blogger, a digital marketer, and a trainer. I love anything related to the Web and I try to learn new technologies every day.
All the team management, content creation, and monetization tasks are handled by me. Together with the team at ExactlyHowLong, the aim is to provide useful and engaging content to our readers.
In game development, I love playing with every different engine, toolset, and framework I can find. In digital art, I love everything from painting to vector work to pixel art to 3D modeling.
In short, if it’s creative and you can make it digitally, I love it.
Summary