Discloses a concentrated liquid nutritional composition comprising: from 5% to 50% by weight protein, on a dry weight basis, wherein at least a portion of the protein is hydrolysed casein having a degree of hydrolysis of from 20% to 80%; wherein the concentrated liquid nutritional composition has a solids content of greater than 50% by weight; and wherein the concentrated liquid nutritional composition has a water activity of less than 0.90. Further disclosed is a method of fortifying breast milk comprising mixing a liquid human milk fortifier with breast milk in a volume to volume ratio of less than or equal to 1:10.