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How long should breast milk be stored in a freezer? :

August 25, 2016

Breast milk can be frozen for up to nine months without losing macronutrients, researchers found.

The Academy recommends storing breast milk for three to six months if frozen in a deep freezer at 0 degrees Fahrenheit (-18 degrees Celsius) or below. The Human Milk Banking Association of North America says milk can be stored under such conditions for up to a year, although less than three months is preferred.

Researchers sought to determine how freezing breast milk affects pH, bacterial counts and nutrient contents. They collected 100 milliliters of milk from 40 mothers. Some of the milk was frozen at -20 degrees Celsius for one, three, six or nine months (fresh frozen), while other samples were refrigerated at 4 degrees Celsius for 72 hours then frozen at -20 degrees Celsius (refrigerated frozen). Both groups of milk were transferred to -80 degrees Celsius until analyzed, the same temperature as a baseline group.

Researchers found milk pH and gram-negative colony counts decreased over the nine months of frozen storage regardless of prior refrigeration. Total bacteria and gram-positive colony counts also declined, most rapidly in the refrigerated frozen milk.

The team noted the importance of “intestinal bacteria and its diversity.”

“In this regard, prior refrigeration before freezer storage may accelerate these potentially deleterious effects on milk microflora,” they wrote.

Over time, the milk’s concentration of non-esterified fatty acids increased, and there was no effect on total protein, fat, lactoferrin, secretory IgA and osmolality.

“These data support current guidelines for freezer storage of human milk for up to nine months for both freshly expressed and refrigerated milk,” authors wrote.

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