Why slippery jacks have slimy caps, and should you peel them?

The slippery jack got its name from exactly this: a slimy, glossy cap that looks as if the mushroom has been brushed with oil. This film is both the slippery jack's main hallmark and the cause of kitchen debates: peel it or not?

Let's sort it out calmly. First, why the slippery jack has this slime at all, then when the skin really should come off and how to do it quickly without turning cleaning into torture.

Why the slippery jack has a slimy cap

The slime on the cap is no accident but a useful adaptation. The film helps the mushroom hold on to moisture and protects the young cap from drying out in a sunny pine forest.

In wet weather the cap is especially shiny because the slime swells. In dry weather it dries out and the cap turns tacky, almost gluey. Pine needles, grains of sand and leaves stick easily to this film, which is why freshly picked slippery jacks often look "dirty."

It's precisely because of this dirt, clinging firmly to the slime, that the skin is usually peeled off. It's not a whim but a practical need: otherwise sand and needles end up in your dish.

Should you peel the skin?

There's no single hard rule here, but there are several good reasons to peel.

• Dirt. Needles and sand stick to the slime and are hard to wash off with water.
• A slightly bitter taste. The skin of some slippery jacks tastes a little bitter, especially in mature mushrooms.
• Slimy texture. In a finished dish the skin makes it overly slimy, which not everyone enjoys.
• Your stomach. In some people the slimy film causes a mild digestive upset.

For all these reasons, most foragers peel their slippery jacks. But if the mushrooms are young and clean and you're cooking them right away, a thorough wash can be enough. For drying, the skin is often left on, since it will dry out anyway.

How to peel the skin quickly and without sticky hands

There's one main trick: peel slippery jacks dry, before washing. Wet skin gets even slimier, and your hands and knife get sticky.

A few tips from experience:

1. Don't wash the mushrooms beforehand; peel them dry right after you get back from the forest.
2. Catch the edge of the skin with a knife near the cap margin and pull toward the center; it will come off in strips.
3. Wear gloves or wipe your hands with a dry cloth from time to time, because the slime stains your fingers brown.
4. Young mushrooms peel more easily, so don't leave them for long.

Drier relatives, such as the bovine bolete or the velvet bolete, have skin that barely peels; just wiping them is enough.

When you can skip peeling

If you've picked young, clean slippery jacks in dry weather, when there's little slime, and you plan to dry them, you can leave the skin on. Likewise, there's no need to struggle with peeling if the mushrooms are going into a soup, where the sliminess isn't noticeable, and you've washed them thoroughly.

The best time to pick slippery jacks is a day or two after a warm rain in coniferous and mixed forests. An easy way to track good windows is our mushroom radar: it shows when moisture and warmth line up well for mushrooms to appear.

Sources

• "Field Guide to the Fungi of Ukraine" (Kyiv, Naukova Dumka publishing house).
• Suillus luteus on GBIF, the global biodiversity database.
• Suillus on MycoBank, the international fungal nomenclature database.
• Suillus luteus on Wikipedia.