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How to Tell if Buttermilk is Bad? [6 Signs & Storage Tips]


Buttermilk is a fermented dairy product with a tart, tangy flavor. However, it is perishable and can go bad if not handled properly. Knowing how to determine if buttermilk has gone bad can help prevent foodborne illness. This article covers signs of fresh and spoiled buttermilk, causes of spoilage, proper storage methods, if you can eat moldy buttermilk, and how long buttermilk lasts refrigerated or frozen. Following these guidelines will ensure you can safely enjoy this tasty ingredient before it expires.

Signs of Fresh Buttermilk

Fresh Buttermilk

Here are indications that buttermilk is still fresh and safe to consume:

  • Thick texture. Fresh buttermilk is creamy and thick, but pourable. It should coat the back of a spoon.
  • Tangy taste. It will have a pleasantly tart, tangy taste when fresh.
  • Clean sour aroma. It smells mildly tangy or sour, without any foul odor.
  • Uniform color. Fresh buttermilk is white with a pale yellow tint. It has no dark spots or discoloration.
  • Smooth surface. There is no separation of whey or lumpy curdling on top when fresh.
  • No mold. Buttermilk that is still good should have no fuzzy mold growth.

Buttermilk exhibiting any changes in texture, smell, taste or appearance may be spoiled.

What Causes Buttermilk to Go Bad?

There are a few reasons why buttermilk can spoil quickly:

  • Bacteria growth. Buttermilk naturally contains lactic acid bacteria. If stored incorrectly, pathogenic bacteria can grow and reproduce rapidly.
  • Yeasts and molds. Exposure to oxygen allows yeasts and molds to grow, causing off-flavors and textures.
  • Temperature abuse. Heat encourages rapid microbe and enzyme activity that deteriorates buttermilk.
  • Age. The lactic acid and fermentation process eventually cause the proteins and fats to break down over time.

Proper refrigeration is key for slowing buttermilk spoilage. The ideal temperature is 38°F or below. Higher fridge temperatures promote faster spoilage.

6 Signs That Your Buttermilk Is Bad

Here are the most common signs that buttermilk has spoiled and should be discarded:

1. Sour Odor

Fresh buttermilk has a mildly tangy smell from lactic acid. As it spoils, the odor becomes sharper and more sour.

If you notice a strong, unpleasant sour aroma, it means the buttermilk is past its prime. Do not consume buttermilk with an “off” smell, as it may contain high levels of spoilage bacteria.

Key Point: There is a distinct, unpleasant sour smell when buttermilk goes bad.

2. Thick Texture

When fresh, buttermilk should have a thin, pourable consistency. As it spoils, buttermilk thickens into a goopy, gelatinous texture.

If your buttermilk has become very thick and gloppy, this indicates it has gone bad and should not be used. The thickened texture is from acid coagulation of milk proteins.

Key Point: Buttermilk thickens to a gummy, glue-like texture when it spoils.

3. Mold Growth

The appearance of mold on the surface or inside the carton is a clear sign buttermilk has gone bad. You may see fuzzy white, black, blue or green mold.

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Do not consume buttermilk with any mold growth. Discard the entire carton, as the mold roots may run deeper than visible and the spores spread easily. Consuming mold puts your health at risk.

Key Point: Mold growth, usually appearing fuzzy or dry on the surface, means buttermilk is spoiled.

4. Separation & Curdling

As it starts to sour, buttermilk may separate into watery whey and thick curds. The curds form from milk proteins clumping together in the acidic environment.

Excessive curdling and separation means the buttermilk is beyond its prime and should be discarded. The texture becomes unusable and unappealing.

Key Point: Buttermilk naturally ferments with age, causing curdling and separation into whey and curds.

5. Off-Colors

Fresh buttermilk is white or pale yellow. As it spoils, the color changes to yellowish-grey, pinkish or orange tints.

Unnatural colors like grey, pink, orange or green indicate microbial contamination and buttermilk that is too far gone. Do not consume discolored buttermilk.

Key Point: The color changes from white/pale yellow to grey, pink, orange or other unnatural shades when buttermilk spoils.

6. Slimy Consistency

Along with thickening, spoiled buttermilk can develop strings or globs of slimy texture. This mucous-like slime comes from rapid bacterial overgrowth as the buttermilk ferments.

Slimy buttermilk has an offensive appearance and texture. Consumption risks possible food poisoning from the high microbial levels, so discard any slimy buttermilk.

Key Point: Bacterial spoilage causes a slimy consistency to develop in bad buttermilk.

How to Store Buttermilk?

Like most dairy items, buttermilk is perishable and has a relatively short shelf life compared to other pantry staples.

Knowing the proper methods for storing buttermilk can help you keep it fresh longer and avoid wasting this useful ingredient.

Here is an overview of the best practices for storing buttermilk:

  • Keep refrigerated at all times.
  • Store in original container until opened.
  • Transfer to an airtight container after opening.
  • Avoid repeated temperature fluctuations.
  • Keep away from light to avoid UV damage.
  • Do not freeze buttermilk unless using later for cooking.
  • Use within 2 weeks of purchase for best quality.

Ideal storage depends first on whether the buttermilk is unopened or opened:

Unopened Buttermilk

  • Leave in original bottle or carton.
  • Store on an interior refrigerator shelf away from the door.
  • Use by expiration date for maximum freshness.

Opened Buttermilk

  • Pour into an airtight glass or plastic container.
  • Make sure lid seals tightly.
  • Use within 10 days.

Following proper storage methods helps extend the shelf life so you can enjoy buttermilk when you need it.

Why Refrigeration is Important

Cold temperatures are vital for keeping buttermilk safe and fresh for as long as possible. Here’s why refrigeration matters:

  • Slows microbial growth – Cold temperatures inhibit the growth of bacteria, mold and yeast in buttermilk. Proper refrigeration at 40°F or below is essential to prevent foodborne pathogens.
  • Retains thickness – Cool temperatures keep buttermilk thick and creamy. Without refrigeration, buttermilk quickly loses viscosity and becomes thin and watery.
  • Minimizes vitamin loss – Heat and light degrade the vitamins like riboflavin in buttermilk. Refrigeration preserves nutrition.
  • Prevents curdling – Buttermilk held at room temperature can curdle prematurely. Refrigeration delays natural separation and extends stability.
  • Inhibits off flavors – Warm conditions allow acidic flavors to become stronger. Refrigeration maintains buttermilk’s tangy yet mellow taste.

For both food safety and quality, refrigerate buttermilk at 40°F or below at all times. Next, we will look at recommended refrigerator placement.

Optimal Refrigerator Placement

Once opened, the ideal place to store buttermilk in the refrigerator is:

  • Inside an airtight container
  • On a middle shelf
  • Away from light exposure
  • Away from ethylene gas producing fruits

Proper placement in the fridge helps prevent undesirable changes to buttermilk:

Airtight container – Prevents absorbing fridge odors or leaking liquid. Look for a tight sealing lid.

Middle shelf – Keeps buttermilk colder than door shelf and minimizes temperature fluctuations from opening fridge.

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Avoid light – Exposure to UV rays degrades riboflavin and fades color. Store in an opaque container away from light.

Away from produce – Fruits like avocado, banana and tomato emit ethylene gas that can accelerate spoilage.

With the right refrigerator placement in an airtight container, buttermilk stays colder and fresher longer.

How Long Does Buttermilk Last Refrigerated?

How long buttermilk lasts depends on the sell-by date and proper storage. General guidelines are:

  • Unopened. About 2-3 weeks past the printed sell-by or use-by date.
  • After opening. 7-10 days.
  • Homemade. 1-2 weeks.

Other tips for maximizing buttermilk shelf life include:

  • Check sell-by date before buying.
  • Refrigerate opened cartons towards the back, where it’s coldest.
  • Keep lid tightly sealed after each use.
  • Don’t return any spilled or used buttermilk back into the original container.
  • Watch for signs of spoilage toward day 7-10 after opening.

How Long Does Buttermilk Last Frozen?

Buttermilk can be frozen but will change in texture and taste. Here are general guidelines for freezer times:

  • Fresh buttermilk: 3-4 months
  • Leftover buttermilk: 4-6 months
  • Homemade buttermilk: 4-6 months

To freeze buttermilk:

  1. Make sure buttermilk is fresh, not expired.
  2. Pour into air-tight freezer containers, leaving 1⁄2 inch headspace.
  3. Seal, label with date, and freeze.
  4. For best quality, use frozen buttermilk within recommended timeframe.
  5. Thaw in fridge before using. Use thawed only for cooking, not drinking.

While freezing extends shelf life, thawed buttermilk will be more curdled, watery and less tangy. It’s best reserved for recipes where texture isn’t important.

Common Buttermilk Storage Mistakes

To get the longest shelf life from buttermilk, avoid these common storage mistakes:

  • Forgetting to refrigerate promptly after purchase or use
  • Transferring to a non-airtight container after opening
  • Storing on refrigerator door where temperature fluctuates
  • Allowing film or dried buttermilk to form around bottle rim before sealing
  • Pouring new buttermilk into a container with old buttermilk remnants
  • Freezing buttermilk without added starch to prevent curdling

Be diligent about refrigeration and proper storage methods. Buttermilk left out or stored improperly can quickly spoil.

How to Substitute Fresh Buttermilk

If you are out of buttermilk, emergency substitutions include:

  • Milk + lemon juice/vinegar – For 1 cup buttermilk, mix 1 cup milk with 1 tablespoon lemon juice or white vinegar. Let stand 5 minutes to curdle.
  • Plain yogurt – Use an equal amount of thick, plain yogurt thinned with milk if too thick.
  • Sour cream – Sour cream diluted with milk works as a 1:1 substitute.
  • Cream + lemon juice – Mix heavy cream with a bit of lemon juice and let stand to curdle slightly before using.

Avoid powdered buttermilk substitute, as it does not have the same properties as real cultured buttermilk. In a pinch, sour milk or yogurt can be used but will change the texture somewhat.

Is It Safe to Consume Moldy Buttermilk?

It is unsafe to knowingly consume buttermilk containing mold. Reasons to discard moldy buttermilk include:

  • Mold roots can penetrate deep into the buttermilk, even if not visible. Consuming can introduce mold into the body.
  • Molds produce allergenic spores that spread easily through the air or contact.
  • Mycotoxins from molds can withstand refrigeration and freezing. Cooking does not neutralize them.
  • Mold imparts unpleasant flavors that ruin the taste of buttermilk.

While it may be possible to salvage some harder cheeses with surface mold, soft dairy products like buttermilk should always be discarded if moldy. Erring on the side of caution helps prevent foodborne illness.

What Happens If You Consume Spoiled Buttermilk?

Drinking or eating food prepared with contaminated buttermilk poses health risks including:

  • Gastroenteritis – symptoms like diarrhea, vomiting, nausea and abdominal cramps.
  • Food poisoning – due to bacteria like salmonella or E. coli producing toxins in spoiled buttermilk.
  • Allergic reaction – some people who are lactose intolerant or allergic may experience discomfort.

Consuming large volumes of severely spoiled buttermilk can cause severe illness requiring hospitalization in sensitive groups like the elderly, infants, pregnant women or immunocompromised people.

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If you accidentally ingest mildly spoiled buttermilk, monitor yourself for symptoms of foodborne illness and seek medical help if they persist. Discard the remainder of the contaminated batch so others don’t consume it.

Can Spoiled Buttermilk Make You Sick?

Consuming buttermilk that has gone bad can cause foodborne illness. The main risks are bacteria, molds and their toxic byproducts.


Harmful bacteria like Salmonella, E. coli, Staphylococcus aureus, Listeria and Campylobacter can grow alongside lactic acid bacteria as buttermilk spoils.

If ingested in high amounts, these pathogens may cause vomiting, diarrhea, abdominal cramps, fever, headache and weakness starting 1-7 days after consumption.

Mold Toxins

Some molds produce toxic compounds called mycotoxins as they break down milk components. Ingesting high levels of mycotoxins from spoiled buttermilk may cause adverse health effects.

However, adverse reactions directly due to mycotoxin ingestion seem uncommon. Still, it is smart to discard buttermilk with mold growth.

Key Point: Bacteria, molds and their toxins make spoiled buttermilk potentially hazardous if consumed.

Is Spoiled Buttermilk Safe for Uses Other Than Drinking?

No, you should avoid using spoiled buttermilk in any way – including cooking, baking or feed for pets. The bacteria and toxins cannot be guaranteed to be destroyed by baking or cooking temperatures.

Consuming spoiled buttermilk risks illness for you and your family. Once buttermilk has gone bad, it is safest to discard it. No uses are recommend for spoiled buttermilk.

Key Point: Do not use spoiled buttermilk for cooking, baking or any other uses. It is unsafe once it has gone bad.

Frequently Asked Questions

1. Can you freeze buttermilk to extend its shelf life?

Yes, freezing is an option for extending buttermilk’s shelf life. Freeze it by the expiration date in an airtight container, leaving headspace to allow for expansion. Thaw in the refrigerator before use within 3-4 months for best quality.

2. Is it safe to consume buttermilk that smells or tastes tangy but is not expired?

No, you should not consume buttermilk with an overpowering tangy or sour smell or taste, even if not expired. This likely means spoilage bacteria have multiplied to potentially dangerous levels, making it unsafe to ingest.

3. Can curdled buttermilk be revived by shaking or stirring?

No, severe curdling and separation mean the buttermilk has spoiled beyond the point of recovery. The proteins have coagulated from the increased acidity and cannot return to solution. Discard buttermilk that is extensively curdled instead of trying to salvage it.

4. How long can you keep homemade buttermilk?

Homemade buttermilk fermented from milk and lemon juice or yogurt cultures should be refrigerated and used within 7-10 days. Since the starting milk is not pasteurized, homemade buttermilk has a shorter shelf life than store-bought. Discard if it has separated, thickened or smells unpleasantly sour.

5. Is it safe to bake with buttermilk that smells a little off?

No, you should avoid using buttermilk with any slightly “off” odors in baked goods or other recipes requiring cooking. The elevated levels of bacteria may survive heating and could still cause foodborne illness if consumed. Only use buttermilk with a fresh smell.


Being able to identify signs of spoiled buttermilk like thickening, odor changes and mold growth allows you to discard it before consumption and potential illness. Properly storing buttermilk sealed at 40°F or below and avoiding contamination helps maximize its shelf life after opening. But once buttermilk shows noticeable signs of spoilage, it’s safest to throw it out regardless of the expiration date or any planned cooking uses. With vigilance, you can catch buttermilk spoilage early and avoid possible foodborne illness for you or your family.

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