Hot leaching of acorns

The most important thing when hot rinsing is to keep an eye on the temperature. In the literature, it is often stated that the acorn is "cooked" during hot leaching, but actually they are meant to be boiled, thus heated to 85–96°C. If they are cooked, the starch in the acorns begins to convert in a process called gelatinization. What then happens is that some of the tannins are permanently bound to the starch molecules. The end product can still be eaten, but will taste bitter. To keep track of the temperature, I use an analog thermometer, digital ones have a tendency to shut off after a while. When I see the temperature starting to approach 95°C, I usually pour in a couple of deciliters of cold water to bring the temperature down again. It has proven to be the easiest way to keep the temperature within the desired range. If you want to leach out large quantities often, it may be worth investing in a so-called electric boiler (available for beer brewing) which can keep the temperature for you so you don't have to stand by the stove all day.

The most important thing when hot rinsing is that the temperature does not get too high. Using a digital thermometer that shuts itself off periodically is not the best option.

Do this:

  1. Peel the acorns and divide them into two halves.
  2. Place them in a pan of water. Use the least 5 liters of water for 1 kg of acorns. With smaller amounts of acorns, relatively more water is needed to reduce the risk of overheating.
  3. Heat the water to 85-96°C. Make sure the water never boils!
  4. Taste the acorns after approx 5 hours. If the bitterness is gone, they are ready, otherwise a little more time is needed. Drain the acorns when you think they are fully leached and wash them in cold water.

Now you can dry the acorns as they are to use them in stews, to steaks or similar. The drying time in an oven or dryer is 12–24 hours at a maximum of 65°C. You can also crush the moist acorns using a mortar and pestle or run them through a meat grinder. Then you will get a nice mass that can be used immediately or dried for later use. The pulp takes 6–12 hours to dry in an oven or dryer at a maximum of 65°C.

A meat grinder is the perfect tool for grinding hot-washed acorns into a smooth pulp that can be dried or frozen.

This post is an edited excerpt from the award-winning book “Nut grower's manual” by Philip Weiss (2022).

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9 thoughts on “Hot leaching of acorns”

  • Interesting, thanks!

    Suggest heating the pot with water and acorns on the stove, with thermometer, then put the pot in the oven at 90°-100°.

    You can of course try it first with just water, but I know for a fact that water will never boil in my oven if it is on 100 grader. Haven't looked at the temperature with a thermometer though, may be it creeps up above 98°. Men, it can be set to 90°, then it should work fine!

  • Must try!
    Men. Hasn't enough energy been used to cook the acorns?.
    Can you imagine freezing, the boiled glans, either the halves or prop, alt. mixed?
    Marie wonders

    • Absolut, it can also be frozen! Which is the most energy demanding (drying/freezing) I don't know though. Last time I dried the leached acorns at room temperature and that went great too. Good luck with your attempts! /Philipp

  • Sous vide should work fine, i.e. a heating rod that can keep the temperature exactly. That way you don't have to worry about heating/cooling.

  • As you mention, a beer brewery should be perfect. 30 L is used by many beginners and can then reasonably handle approx 5-6 kg of acorns. You can heat in a controlled manner and then lift the inner vessel so that the leachate can be drained out. Then rinse with water. Do you usually take care of the starch in the leachate?

    • Unfortunately, I did not manage to get any starch out during hot rinsing. Could it be that it is converted into something else in the process? I will try again this year and observe better…

      • Well, starch is broken down into sugars with the help of various enzymes at 60-70 grader. This is the very principle of brewing beer. If one avoids passing this temperature range, but submerging the acorn directly in hotter water will denature any enzymes immediately. My guess is that this is a question that should be well known. Historically, starch has been extracted from all sorts of crops.

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