Whether you are returning to work, building a freezer stash, or simply want the flexibility of having expressed milk available, knowing how to store breast milk safely is essential. Proper storage preserves the nutritional and immunological properties of your milk while keeping it safe for your baby to consume.
Preparing to Express and Store
Safe storage begins before you even express your milk. Start with clean handsâwash thoroughly with soap and water for at least 20 seconds before handling pump parts or storage containers. If washing facilities are not available, use alcohol-based hand sanitiser with at least 60% alcohol.
Ensure all pump parts that contact breast milk are clean and dry. If you are storing milk, have your clean, food-grade storage containers ready before you begin expressing.
Choosing Storage Containers
The right container makes a difference in maintaining milk quality:
- Glass containers: Excellent choice as they are durable, easy to clean, and do not leach any chemicals into milk
- Hard plastic containers: Look for BPA-free containers designed for food storage or specifically for breast milk
- Breast milk storage bags: Convenient, pre-sterilised, and space-efficient in the freezer. Use bags designed specifically for breast milk, not regular food storage bags
Regardless of container type, always leave some room at the top as milk expands when frozen. Seal containers tightly to prevent contamination and odour absorption.
Always label stored milk with the date it was expressed. If your baby attends childcare, include their name on the label as well. Use the oldest milk first to ensure nothing goes to waste.
Storage Guidelines
Follow these evidence-based guidelines for safe breast milk storage:
Freshly expressed milk:
- Room temperature (up to 26°C): Up to 4 hours (ideally use within 4 hours)
- Insulated cooler bag with ice packs: Up to 24 hours
- Refrigerator (4°C or below): Up to 72 hours (store at the back, not in the door)
- Freezer (-18°C or below): 6-12 months (quality is best within 6 months)
Previously frozen milk (thawed in refrigerator):
- Room temperature: Up to 4 hours
- Refrigerator: Up to 24 hours
- Do not refreeze
Milk left over after a feed:
- Use within 2 hours
- Discard after 2 hours as bacteria from baby's mouth can multiply
When in doubt, remember the "Rule of 4s" for fresh milk: 4 hours at room temperature, 4 days in the fridge, or 4-6 months in the freezer for best quality.
Storing Milk at Work or Away from Home
If you are expressing at work or while out, proper storage is crucial. Expressed milk should be refrigerated as soon as possible. If no refrigerator is available, use an insulated cooler bag with frozen ice packsâthis keeps milk safe for up to 24 hours.
Tips for workplace storage:
- Store milk in the back of the office refrigerator, not in the door
- Use a small cooler bag to transport milk if the office fridge is shared
- Label your containers clearly with your name and the date
- Consider having backup frozen milk at home in case of storage issues
Freezing Breast Milk
Freezing preserves breast milk for longer-term storage. For best results:
- Chill fresh milk in the refrigerator before freezing
- Freeze milk in small portions (60-120ml) to minimise waste
- Store bags flat to freeze, then stand upright to save space once frozen
- Keep milk at the back of the freezer where temperature is most consistent
- Avoid storing in the freezer door where temperature fluctuates
You can add fresh milk to already frozen milk, but cool the fresh milk first and ensure the amount you are adding is less than what is already frozen.
Thawing Frozen Breast Milk
Proper thawing preserves the quality of your milk:
Preferred method: Thaw overnight in the refrigerator. This is the safest method and best preserves nutrients.
Faster methods:
- Place sealed container in warm (not hot) water
- Hold under warm running water
- Use a bottle warmer designed for breast milk
Microwaving breast milk destroys beneficial antibodies and can create dangerous hot spots that can burn your baby's mouth. Always use gentle warming methods.
Warming Refrigerated Milk
Many babies are happy to drink milk at room temperature or even straight from the fridge. However, if your baby prefers warm milk:
- Place the container in warm water for several minutes
- Use a bottle warmer
- Run warm water over the sealed container
Gently swirl (do not shake vigorously) the milk to mix any separated fat. Test the temperature on your inner wrist before feedingâit should feel lukewarm, not hot.
What is Normal for Stored Milk?
Stored breast milk may look different from fresh milk, and this is usually normal:
- Separation: Fat rises to the top. Gently swirl to remixâthis is completely normal
- Colour variations: Milk can range from white to yellow to bluish. Colour can change based on your diet and is normal
- Soapy smell after thawing: Some mothers have high lipase activity, causing a soapy smell. The milk is safe but some babies may refuse it. Scalding fresh milk before freezing can prevent this
Signs milk has spoiled:
- Strong sour smell (distinct from the normal slightly sweet smell)
- Curdled appearance that does not mix when swirled
- When in doubt, do not use it
Combining Milk from Different Sessions
You can combine milk expressed at different times, but follow these guidelines:
- Cool fresh milk before adding to already refrigerated or frozen milk
- When combining, the storage time is based on when the oldest milk was expressed
- Only combine milk from the same day
Transporting Stored Milk
When transporting breast milk (to childcare, when travelling, etc.):
- Use an insulated cooler bag with ice packs
- Pack frozen milk last so it stays coldest
- Refrigerate or freeze immediately upon arrival at your destination
- For air travel, breast milk is exempt from liquid restrictions