Quality After Freezing: What to Do About Cracked, Dried-Out Wrappers

Frozen dumplings and frozen buns are the mainstay of many factories, but open the bag after freezing and you find streaks of cracks across the wrapper and dry, white edges, and they burst as soon as they're boiled. Some of these problems are caused by the freezing method; others were set up by the recipe and the earlier production steps.

Why Do Frozen Dumpling Wrappers Crack?

There are several common causes, and they often occur together:

• Freezing too slowly, ice crystals too large: Water in food forms ice crystals as it freezes. The larger the crystals, the more they rupture the structure, making the product more likely to break when thawed or cooked.
• Surface moisture loss: The air in a freezer is very dry. On products that aren't well wrapped, surface moisture slowly sublimates away and the wrapper becomes dry and brittle, commonly called "freezer burn."
• Temperature fluctuation: When the freezer door is opened often or the unit defrosts, the product temperature goes up and down, and ice crystals repeatedly melt and refreeze, growing larger each time.
• Water released by the filling: The water in the filling expands as it freezes and cracks the wrapper from the inside, then seeps out on thawing. See Dewatering Vegetable Fillings.
• Wrapper too thin or uneven: The thin spots crack first. See Wrappers Too Thick, Too Thin, or Uneven.

How Is Quick Freezing Different from Regular Freezing?

Taiwan's Food and Drug Administration (TFDA) explains that in typical foods, most of the water freezes between about -1°C and -5°C; this range is called the "zone of maximum ice crystal formation." The longer the product stays in this range, the larger the ice crystals grow and the more likely they are to rupture the structure.

• Regular freezing: The product is placed in a freezer and cooled slowly, spending a long time passing through the zone of maximum ice crystal formation, so the crystals are large.
• Quick freezing: Cold, high-velocity air or specialized equipment freezes the product through rapidly, so it passes through this range quickly. The crystals are small and even, the structure stays more intact, and the wrapper is less likely to crack.

IQF (individually quick frozen), common in industry, works on the same principle: products are frozen piece by piece, which also keeps them from sticking together.

How to Adjust the Recipe

1. Control water content and gluten strength: A wrapper with moderate gluten strength tolerates freezing better. Research has also found that flour protein content is positively correlated with the tensile strength of dumpling wrappers. See Flour Types and Machine Forming and Water Absorption Rate.
2. Improve water retention: Some producers use water-retaining food ingredients or additives so the wrapper is less prone to drying and cracking. Confirm compliance with regulations before use; see Using Dough Improvers, Emulsifiers, and Additives.
3. Deal with filling moisture first: Dewater vegetables, and don't add too much water to meat filling.
4. Keep the wrapper evenly thick: If thickness is uniform during forming, the wrapper won't crack from thin spots during freezing.

What You Can Do in Production and Storage

• Get products into the freezer as soon as possible after forming; don't leave them at room temperature too long. A surface that dries before freezing is more likely to crack.
• Package only after the product is frozen through, and seal the packaging to reduce contact with dry, cold air.
• Open the freezer door less often and keep the temperature stable. Article 8, Subparagraph 7 of Taiwan's Regulations on Good Hygiene Practice for Food (食品良好衛生規範準則) states that during transport, the ambient temperature in a frozen food compartment must not exceed -12°C; for storage temperatures, follow the current annex of the Regulations.
• Use first in, first out, so products don't sit in the freezer too long.

Dong-Yih Machinery's DY-201 Automatic Steamed Bun and Mantou Machine can make meat buns, vegetable buns, xiaolongbao, and other common frozen dough products. To discuss production planning for frozen products, call us at 06-257-4644.

FAQ

Q: Why do frozen dumpling wrappers crack?
A: Common causes are freezing too slowly so ice crystals grow too large, surface moisture loss, freezer temperature fluctuation, water released by the filling, and uneven wrapper thickness.

Q: How is quick freezing different from regular freezing?
A: Quick freezing moves the product rapidly through the zone of maximum ice crystal formation at about -1°C to -5°C, so the ice crystals are small and the structure stays more intact.

Q: What should I do if dumpling wrappers dry out after freezing?
A: Seal the packaging immediately after the product is frozen through, reduce freezer door openings and temperature swings, and use first in, first out.

Q: How can the recipe be improved?
A: Control water content and gluten strength, reduce water released by the filling, keep the wrapper evenly thick, and if necessary use legally permitted water-retaining ingredients.