Gravy will often weep when defrosted after freezing. Can it be rescued?
To test if gravy weeps when defrosted, we made two batches of gravy, one thickened with cornstarch and one with flour (the two most common gravy thickeners), and froze them. Once defrosted, both batches wept. Wondering why, we asked our science editor, who explained that when gravy is thickened with flour or cornstarch, the starch granules release long, straight chains of glucose called amylose. The stringy amylose molecules tangle and form a netlike structure that gives the gravy its thick consistency. When gravy cools, the amylose crystallizes and the netlike structure breaks down, causing it to weep or break.
Is it fixable? Our science editor recommended reheating the defrosted gravy to reverse the crystallization and re-form a stable gel. Following his advice, we found that if we brought the gravies to a full boil and then whisked them vigorously, the previously broken gravies were returned to their normal thick, emulsified consistency.
THE BOTTOM LINE: If your defrosted gravy looks weepy or separated, bring it to a full boil on the stovetop and whisk thoroughly, and it will emulsify again.