Hands should be thoroughly washed, preferably with soap and water, before expressing milk. This will minimize the risk of transferring pathogens onto the milk. Washing hands does not prevent stored milk from developing pathogens due to ineffective storage methods.
Containers used for human milk expression and collection must be completely dismantled and washed with warm water and soap then thoroughly air dried or dried with a towel or paper towel.
Do not wash tubing.
Fresh pumped human milk can be stored at room temperature. The amount of time it can be stored at room temperature varies depending on the cleanliness of the milk collection technique and the temperature where the milk is stored; for example did you wash your hands before expressing? Was the expression and collection equipment thoroughly washed and properly dried?
Room temperature guidelines: in 80-85 degrees 4 hours is a reasonable limit. With optimal hand washing and cleanliness of collection equipment and a lower temperature, 6 hours is a reasonable timeline.
If you are expressing milk to feed your baby at the next feed, within 3-4 hours, it is safe to keep the milk at room temperature as long as the temperature does not exceed 85 degrees. If you are not going to use freshly expressed milk within 3-4 hours then refrigerate it as soon as it is expressed or as soon as possible.
Insulated cooler bags with ice packs: there have been very few studies done to evaluate milk at this temperature (typically 59 degrees). Hamosh et al found that based on minimal bacterial growth in the milk samples used in their studies, milk is safe at 59 degrees for 24 hours.
Refrigeration: there have been several studies done on refrigerated (39.2 degrees) human milk storage to evaluate bacterial growth, fat retention, lipase activity, immunity factors and lactoferrin levels. Due to these variant results, it is recommended that you limit refrigeration storage of human milk to 48-72 hours. If you are not going to use the milk within 2-3 days then freeze it as soon as possible. Of course, the timeline is impacted by proper hand washing prior to milk collection and the cleanliness of the milk expression equipment.
Freezing human milk (-4 degrees to 24.8 degrees) : studies have demonstrated that human milk is safe for at least 3 months when frozen. Based on other known factors about frozen foods it is reasonable to freeze milk for 3-6 months. Of course, it is always optimal to use milk as soon as possible. Studies have shown that fat, protein, and calories decrease in human milk when frozen for 90 days compared to fresh human milk. Frozen human milk has a significant increase in acidity by 3 months, likely due to ongoing lipase activity, that increases free fatty acids in the milk (see the protocol noted below on human milk and lipase).
Safety guideline of mixing milks: freshly expressed milk should NOT be added to chilled or frozen milk because this warms the cooled milk thus increasing the opportunity for bacterial proliferation. Freshly expressed milk should be cooled down at room temperature for 30-60 minutes then it can be safely added to refrigerated milk. Do NOT add freshly expressed, room temperature, or refrigerated milk to frozen milk.
Tips for freezing milk: make sure the storage bag is tightly sealed!! Date the milk AND note the amount (milk expands when it is frozen so it can be difficult to discern what the volume is once it is frozen). If your child will attend day care make sure to write your child's FULL name on each bag. Because milk expands when frozen, make sure to leave space at the top of the storage bag to accommodate for the expansion.
There is only ONE study regarding human milk quality after 6 months of freezing so we truly do not have enough information to determine the retained qualities of human milk after prolonged freezing times (greater than 6 months).
Use of Stored Human Milk
Refrigerated and frozen milk can have a different odor than fresh expressed milk, due to lipase activity which can oxidize released fatty acids. There is NO reason to assume that your child will not drink milk with high lipase activity. If you are planning on freezing significant amounts of milk, it may be reasonable to test out frozen milk at about 2-6 weeks after it has been frozen.
Wash hands thoroughly, with soap and water, when preparing to handle stored human milk. Make sure that all feeding containers that you will transfer the stored milk into are thoroughly washed with soap and water and properly dried.
ALWAYS use fresh milk FIRST!!! It has the highest level of immunity protective qualities and higher nutritional quality.
Thawing frozen milk: thawing milk overnight in the refrigerator retains the most amount of fat. Ideally, place the frozen milk bag(s) in the refrigerator the evening prior to its use. If you need to thaw milk out quickly you can place it in a container with warm to hot water. Do not place milk of any temperature or state directly on direct heat. Microwaving can cause variable temperatures in the milk and it decreases immunologic properties of the milk. Because there is no information on the safety of refreezing thawed milk and because of what we know about bacterial proliferation, you should NOT refreeze thawed milk.
Previously frozen human milk that has been thawed should not be left at room temperature for longer than 2 hours.
Once human milk has been thawed, it must be used within 24 hours to minimize bacterial growth.
Left over milk from a feed: there is insufficient research in this area. What you need to know is that human milk left over from a feed has bacterial contamination from the baby's mouth/saliva. Following food safety guidelines, you should refrigerate the left over milk as soon as the feed is over and use it within 1-3 hours afterwards. Just as with all stored human milk, the cleanliness of the original expression process and storage protocol impacts the viability and timeline.
Warming milk: different babies like or accept different temperatures. There is no quality impact related to the temperature of the milk that baby drinks. Some babies drink cold milk, others room temperature and yet others prefer warmed milk. Remember to NEVER apply direct heat. You can use a waterless warmer. You can also warm water in a pot on the stove then remove the pot from the burner (to eliminate radiant heat) and put the cold milk into the pot until desirable temperature is achieved.