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Question
In our kitchen we have been successfully producing frozen potatoes. We blanch and then freeze russet potatoes, however after storing them in the freezer they are turning black. We follow all the necessary steps, we have done research and even altered our steps to prevent the browning, but we froze over 50 pounds of red and russet potatoes and the majority of them turned brown. We don't add any vinegar or additives to the potatoes as we are trying to keep them as organic as possible. What are we missing?
This is a fairly common issue when freezing fresh potatoes, even when the blanching step is included. The discoloration is usually caused by enzymes that cause browning not being fully inactivated, or by oxidation before the potatoes freeze.
Blanching time
Blanching is what stops the enzymes that cause browning. If the blanch time is too short, those enzymes can continue working even in the freezer.
Typical blanching times are about 3 - 5 minutes for diced potatoes and 5 - 7 minutes for whole or larger pieces, and the water should be at a full rolling boil before adding the potatoes.
Cooling after blanching
After blanching, potatoes should be immediately placed into an ice water bath to stop the cooking process. They should remain in the ice water for roughly the same amount of time as they were blanched.
Oxygen exposure before freezing
If potatoes sit out after blanching, they can begin oxidizing and darkening. It helps to drain and dry them well and freeze them as quickly as possible, ideally spread in a single layer at first.
Freezing temperature
A freezer should be 0°F (-18°C) or colder. Slow freezing or stacking potatoes too thick can contribute to discoloration.
Variety differences
Red potatoes can sometimes darken more easily during freezing because they contain higher levels of natural compounds that are prone to oxidation.
Natural color protection
Even many organic processors will use small amounts of ascorbic acid (vitamin C) or citric acid in the blanch water to help stabilize color. These are considered natural ingredients and are commonly used in frozen vegetables.
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