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Question

Why are our fries turning dark blue/black before service when we blanch them at 180°C after soaking them in water for 1–4 days, and how can we prevent it?

In our kitchen, we blanch our fries in the fryer using the oil blanching method. Our fries have been cut and placed in a bucket of water, fully submerging them, where they sit in the walk-in for anywhere from 1-4 days. We pull the buckets, dump the fries into a large strainer and let sit.

Once dry, we fill each basket with the fries and drop each basket for 45 seconds. Fryer is at 180⁰C. We let the baskets hang for 15 mins to allow the oil to drop off as much as possible. The fries are put onto a sheet tray and put in the walk-in to cool before panning them up in a large container, wrapped tight or with a lid.

9 times out of 10 our fries start to turn dark blue/black before the dinner service is over. Any suggestions?

Answer

You’ve got a sugar and oxidation issue going on.

What’s likely happening:

  • Holding cut fries in water for 1–4 days is too long. They start converting starch to sugar
  • More sugar = fries turning dark or almost black when fried
  • Oxidation after cutting and after blanching adds to the discoloration
  • If your raw potatoes are stored too cold, that also increases sugar levels

What to change:

  • Cut and soak fries no more than 24 hours, same day is best
  • Rinse well before blanching to remove excess starch and sugars
  • Add a little vinegar or lemon juice to the soak water to slow discoloration
  • Don’t overload fryer baskets so they blanch evenly
  • After blanching, spread them out to cool quickly instead of stacking

Big one to check:

  • Make sure your raw potatoes are not stored too cold
  • Ideal storage is around 45–50°F. Colder than that builds sugars and causes dark fries

If you fix the soak time and storage temp, you’ll likely solve most of the problem right away.

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