How can you tell if frozen breast milk is bad?

When storing expressed breast milk, it’s important for moms to know the signs of spoiled milk, so they don’t accidentally feed bad milk to their baby. Fortunately, there are several ways to tell if frozen breast milk has gone bad.

Check the color

Fresh breast milk is white or cream colored. As it starts to spoil, the color changes. Bad breast milk may look yellow, chunky, separated, or curdled.

Spoiled breast milk may also develop a pinkish hue. This is from an overgrowth of bacteria. While the change in color doesn’t necessarily mean the milk has spoiled, it does indicate it’s time to start investigating further.

Give it a sniff test

Fresh frozen milk should not have a strong odor. It may smell faintly sweet. If you detect a sour, rancid, or rotten odor, however, that indicates spoilage.

The bacteria and enzymes that cause milk to spoil give off these unpleasant smells. Bad frozen breast milk may also smell soapy or metallic.

Check the taste

Never skip directly to tasting milk if you detect an off odor. However, if the milk has been thawed and smells okay, take a small sip. Fresh milk should taste mildly sweet with no sour or bitter flavors.

Spoiled milk will immediately taste rancid, metallic, or soapy. The acidity increases as milk turns, creating a sour taste. If it tastes off, err on the side of caution and don’t feed it to your baby.

Examine the consistency

Frozen breast milk separates into layers as the fat rises, which is perfectly normal. Gently swirl the bottle after thawing to remix any separated milk.

However, lumps, chunks, and a curdled appearance indicate spoilage. This happens as milk proteins and fats degrade. If you see any clumping or curdling, do not use the milk.

Check for contamination

Always inspect milk for signs of contamination before feeding it to your baby. Look for dirt, debris, mold, or blood. Bloody milk may simply indicate cracked nipples rather than spoilage, but err on the side of caution and discard it.

Watch the storage time

The storage time is a good indicator of whether frozen breast milk is still good. Here are some general guidelines on how long it stays fresh:

  • Countertop: Up to 4 hours at room temperature (up to 77°F or 25°C).
  • Refrigerator: Up to 4 days at 39°F (4°C) or lower.
  • Freezer: Up to 6 months in a deep freezer at 0°F (-18°C) or lower. Up to 3-6 months in a self-defrosting freezer.
  • Thawed, previously frozen milk: Up to 24 hours in the refrigerator before discarding.

Always label milk storage containers with the date it was expressed. That allows you to keep track of recommended storage times. Exceeding these timeframes increases the risk of spoilage.

Watch for separation

As mentioned, some separation of breast milk into layers is normal when thawing frozen milk. However, thick, chunky separation can indicate spoilage.

Shake the bottle gently to remix any thin separation. If the milk doesn’t blend smoothly, however, it is likely spoiled.

What causes breast milk to spoil?

Breast milk spoils from the growth of bacteria and the breakdown of fats, proteins, and sugars. Contamination and improper storage speeds up these processes. Here are some common causes of spoilage:

  • Leaving milk out too long at room temperature.
  • Allowing bacteria from hands, bottles, or pump parts to contaminate the milk.
  • Storing milk in the door of the refrigerator, where temperatures fluctuate.
  • Exceeding refrigeration time guidelines.
  • Not immediately refrigerating or freezing milk after pumping.
  • Not fully thawing frozen milk before the next refrigeration.
  • Exceeding freezer storage time guidelines.
  • Power outages or freezer failures leading to temperature changes.
  • Not washing hands properly before handling milk collection or storage containers.

Can you re-freeze breast milk once thawed?

Previously frozen breast milk can be safely re-frozen, but only under certain conditions:

  • Thawed milk can be refrigerated for up to 24 hours before it must be used or discarded.
  • Only re-freeze milk that was thawed in the refrigerator, not at room temperature.
  • Do not re-freeze milk that has been warmed after thawing.
  • Milk that was previously frozen should only be re-frozen once.
  • Label milk with the initial pump date and dates of freezing, thawing, and re-freezing.
  • Consume re-frozen milk within 24 hours of thawing.

Can you microwave thawed breast milk?

Thawed breast milk can be safely microwaved, but use caution not to overheat it. Here are some microwave heating tips:

  • Transfer milk from the freezer bag or bottle into a glass or BPA-free bottle before microwave heating.
  • Microwave in short intervals, such as 5-10 seconds at 50% power. Avoid boiling.
  • Gently swirl or shake the bottle after each interval to distribute the heat evenly.
  • Stop heating when the temperature reaches about 98°F.
  • Always test the temperature by dropping some milk onto your wrist before feeding baby.
  • Discard any leftovers rather than re-refrigerating after baby is done eating.

Can you save breast milk if only part of it smells bad?

If only a portion of thawed or refrigerated milk smells spoiled, the remainder cannot be safely saved. Bacteria and enzymes that cause rancidity can spread through the milk quickly. Discard all of the milk to ensure none of the contaminated portion is fed to your baby.

Should you scoop breast milk from the top or bottom of storage?

When retrieving stored milk, avoid just pouring out or scooping from the top layer. The cream and fat content in breast milk separate and rise over time. Pouring from the top results in milk that is higher in fat than usual.

Instead, gently swirl or invert the chilled storage container several times to remix any separated milk before pouring or scooping out a feeding portion. This helps ensure your baby gets a consistent ratio of fat and nutrients in every ounce.

Can thawed breast milk be donated?

Previously frozen milk that has been thawed is no longer suitable for donation. Milk banks require human milk donations to be in their original fresh state. Thawed milk has a shorter shelf life and raises the risk of bacterial contamination.

However, thawed milk is perfectly safe for your own baby if it has been properly stored and shows no signs of spoilage. Follow milk bank guidelines on the handling and storage of milk intended for donation.

Does alcohol in breast milk kill good nutrients?

Moderate alcohol consumption does not destroy significant nutrients in breast milk. However, alcohol does pass freely into breast milk and should be avoided. Here are some key points on alcohol and breastfeeding:

  • Even moderate drinking spreads alcohol into breast milk, enough to affect a baby’s developing brain and motor skills.
  • Pumping and dumping does not speed the clearance of alcohol from milk. The milk remains contaminated as long as alcohol remains in the mother’s blood.
  • Alcohol in breast milk peaks about 30-60 minutes after mom consumes a drink.
  • For mom’s occasional drink, wait at least 2 hours (per standard drink) before nursing to allow alcohol to clear her system.
  • Store enough breast milk or supplement with formula to allow baby a feeding during those 2+ hours.

The safest choice is avoiding alcohol altogether while breastfeeding. But an occasional drink should not damage the nutritional profile of your milk as long as you allow adequate sober time before the next feeding.

Does caffeine affect breast milk nutrition?

Caffeine does pass into breast milk and can accumulate to affect baby if mom consumes too much. However, moderate caffeine intake (2-3 cups of coffee daily) does not appear to cause significant issues or alter milk nutrition. Here are some tips on minimizing caffeine exposure:

  • Limit yourself to 300 mg of caffeine per day (about 2-3 cups of coffee).
  • Consume caffeine through beverages mainly in the morning rather than afternoon/evening.
  • Wait at least 2 hours after caffeine intake before nursing.
  • Switch to water, juice, decaf or herbal tea in the afternoons/evenings.
  • Avoid energy drinks – these are very high in caffeine.

Caffeine does not damages nutrients itself. But too much can overstimulate baby, interfering with sleep patterns and feeding. Moderation minimizes caffeine transfer to baby while allowing mom her morning pick-me-up.

Signs of spoiled breast milk in baby

If you accidentally feed spoiled milk to your baby, watch for these possible signs of a reaction:

  • Fussiness or refusal to eat
  • Increased spit-up or vomit
  • Diarrhea
  • Bloating or gassiness
  • Constipation

Severe spoilage may also cause fever, blood in the stool, cough/breathing issues if aspirated, or lack of appetite. Contact your pediatrician if you notice multiple symptoms.

Discard any remaining spoiled milk so baby is not exposed again. Monitor for several hours to ensure symptoms resolve on their own as the milk passes through their system.

How to prevent breast milk from spoiling

Proper collection, storage, and handling prevents most breast milk spoilage. Here are some top tips for keeping your liquid gold fresh:

  • Wash hands – Wash thoroughly with soap and water before pumping or handling milk collection.
  • Sterilize equipment – Ensure pump parts, bottles, caps, etc are properly sterilized per instructions.
  • Seal containers – Use a tight-sealing bottle or bag designed for breast milk storage.
  • Small portions – Store 2-4 ounce portions to avoid waste if milk spoils.
  • Label – Mark all containers with date pumped and use-by dates.
  • Quick refrigeration – Refrigerate promptly after pumping, within 4 hours.
  • Back of fridge – Place toward the back of the main body of the fridge.
  • Thaw safely – Thaw frozen milk overnight in the fridge. Do not leave out at room temperature.
  • Single re-freeze – Only re-freeze thawed milk once.


Checking for changes in smell, taste, color, and consistency are the best ways to determine if frozen breast milk is still good. Follow safe storage guidelines, watch for signs of spoilage after thawing, and smell/taste test before feeding to baby. With proper precautions, moms can safely store milk for many months.

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