Storing Breast Milk: Safety Guidelines and Tips

Once you start expressing milk, knowing how to store it safely makes a real difference. Good storage habits protect the nutritional value of your milk and keep it safe for your baby.

Storage Times at a Glance

How long breast milk stays safe depends on where you store it:

• Room temperature (up to 25°C / 77°F): up to 4 hours
• Refrigerator (4°C / 39°F): up to 4 days — store at the back of the fridge, not in the door
• Freezer (-18°C / 0°F): up to 6 months for best quality, acceptable up to 12 months

When in doubt, shorter is better. Freshly expressed milk retains the most beneficial properties, so use the freshest milk available when you can.

Choosing the Right Containers

Store your milk in clean, food-grade containers — either hard-sided bottles with tight lids or breast milk storage bags designed for freezing. Avoid regular plastic bags or disposable bottle liners, which can tear or leak.

A few practical tips:

• Label every container with the date and volume
• Leave room for expansion if you plan to freeze — milk expands as it freezes, so don't fill containers to the top
• Store in small portions (60–120 ml) to reduce waste, since you'll need to use thawed milk within a set time

Thawing and Warming

When you're ready to use frozen milk:

• Thaw in the fridge overnight for a gentle, gradual thaw
• Or hold under lukewarm running water if you need it sooner
• Never microwave breast milk — microwaving creates hot spots that can burn your baby's mouth and destroys some of the milk's beneficial components
• Swirl the container gently to mix the fat that naturally separates — vigorous shaking is not necessary
• Use thawed milk within 24 hours and do not refreeze it

Mixing Milk from Different Sessions

You can combine milk expressed at different times, but there's one important rule: cool freshly expressed milk in the fridge before adding it to already-chilled or frozen milk. Adding warm milk directly to cold or frozen milk can partially thaw the stored portion and affect its quality.

Once both portions are the same temperature, you can combine them in one container.

When to Discard Breast Milk

It's better to be cautious than to risk giving your baby milk that may no longer be safe:

• If milk smells sour or off — breast milk can have a slightly soapy smell due to lipase, which is normal, but a distinctly sour or rancid smell means it should be discarded
• If storage times have been exceeded — follow the guidelines above
• If your baby didn't finish a bottle — use the remaining milk within 1–2 hours, then discard it, as bacteria from your baby's mouth can enter the milk

A Note on Lipase

Some parents notice their stored milk develops a soapy or metallic smell. This is usually caused by lipase, an enzyme that breaks down fat in the milk. It's not harmful, but some babies may refuse the taste. If this happens, you can scald the milk briefly before storing — heating it until small bubbles form at the edges, then cooling and freezing it quickly.

This article draws on information from Ammehjelpen. You can find the original guidance there.

This content is for informational purposes only and does not replace professional medical advice. Consult your healthcare provider for personalised guidance.