Why Do Mushrooms Discolor After Cutting?

Mushrooms are a popular ingredient in many dishes, adding an earthy, umami flavour to salads, stir-fries, and sauces. However, they can be tricky to work with due to their tendency to discolour. This phenomenon is especially noticeable when cooking mushrooms with other ingredients, as they can give a dull grey tint to the entire dish. While this discolouration may be undesirable for aesthetic reasons, it is typically safe to consume unless the mushrooms also exhibit other signs of spoilage, such as a slimy texture, dark spots, or an unpleasant odour. Interestingly, the discolouration is mostly concentrated in the gill parts of the mushrooms. Additionally, certain varieties of mushrooms, known as magic mushrooms or Psilocybe, instantly develop a blue colour when cut or bruised due to the presence of psychotropic compounds.

Why do magic mushrooms turn blue when cut?

Mushrooms, especially the Psilocybe species, are known to instantly develop a blue coloration when they are cut, plucked, bruised, or mishandled. This phenomenon has puzzled scientists for decades, but recent research has unravelled the mystery behind it.

The blue coloration of magic mushrooms is due to the oxidation of psilocybin, the psychoactive compound in these mushrooms. When magic mushrooms are damaged, a phosphatase enzyme takes off its phosphate group, converting psilocybin into psilocin. An oxidizing laccase then creates psilocyl radicals, which combine to form C-5 coupled subunits and then further polymerise via C-7. The pigment is not a single compound but a complex mixture of linked psilocybin oxidation products. These pigments are similar to indigo, the dye used to produce blue jeans.

While the exact purpose of the blue pigments is unknown, one hypothesis is that they may serve a protective role, acting as an on-demand repellent against predators. The compounds might produce reactive oxygen species, which could be toxic to insects that nibble on the mushrooms.

The blueing of magic mushrooms is a natural and harmless chemical reaction. However, it can reduce the potency of the mushrooms. Therefore, it is important to handle and store them properly to preserve their potency. Drying the mushrooms correctly and storing them in a cool, dark, and dry place can help minimize oxidation.

Preventing discolouration when cooking mushrooms

Mushrooms are a tasty addition to many dishes, but they can sometimes discolour when cooked. This is due to the release of moisture, which can cause a grey tint in the pan, and also because of oxidisation.

To prevent discolouration when cooking mushrooms, there are several steps you can take. Firstly, it is important to store mushrooms correctly. Keep them in a paper bag in the fridge, which will allow any moisture to escape. Aim to use fresh mushrooms within 3-4 days of purchasing, as they do not have a long shelf life. If you are not using them within this time frame, you can also freeze mushrooms for up to 12 months.

When preparing mushrooms, it is best to slice them just before cooking, as exposing them to air for too long can cause them to discolour. If you are cooking mushrooms with other ingredients, salt them to draw out moisture, and make sure the pan is not crowded so that the moisture can cook off effectively. You could also try removing the gills of the mushrooms, as this is where most of the discolouration comes from.

If you are still concerned about discolouration, you can cook mushrooms separately from other ingredients and combine everything at the end. This will prevent any discolouration from affecting the rest of your dish.

How to identify if mushrooms have gone bad

Mushrooms are a great ingredient to add an earthy, umami-rich flavour to your recipes. However, they don't have a long shelf life and can show signs of spoilage quickly. Here are some tips to identify if mushrooms have gone bad:

Appearance

Mushrooms that have gone bad will have a slimy texture. They will look and feel wet and slippery. If the mushrooms have bruises, dark spots, or are slightly darker in colour than usual, they are starting to go bad. The surfaces of fresh mushrooms should be dry and appear plump. If your mushrooms have developed dry patches and don't look as plump as they used to, it's a sign that they are about to go bad.

Smell

Mushrooms that have gone bad will have an unpleasant, fishy or sour odour. Bad mushrooms can make you sick due to bacteria that has started to form.

Spoilage

If your mushrooms have developed a thin layer of slime, it can lead to mould. Spoiled mushrooms could contain bacteria that can cause food poisoning or botulism.

Storage

When buying mushrooms, avoid pre-packaged containers. Instead, buy loose mushrooms so you can inspect their quality. After buying, take them out of the original container. If stored in a plastic wrap, mushrooms will collect moisture on the surface and start to discolour and turn brown after five to seven days. Instead, transfer them to a brown paper bag and set it in the fridge. This will keep any moisture at bay.

Cooking

If you're cooking mushrooms with other ingredients, consider cooking them separately to avoid discolouration. Salting them can also help draw out moisture.

Poisonous mushrooms

It is important to distinguish between poisonous and edible mushrooms. Some poisonous mushrooms can kill, so you must be able to accurately identify the mushroom before consumption. Avoid mushrooms with white gills, a skirt or ring on the stem, and a bulbous or sack-like base called a volva. Amanita is a very common genus of mushroom, and some of the most toxic types belong to this group. They can be identified by their dry, umbrella-shaped caps and white gills.

Properly storing mushrooms to prevent discolouration

Mushrooms are a great ingredient to add to your meals, but they don't have a long shelf life and can show signs of spoilage quickly. To prevent discolouration, it is important to store mushrooms properly. Here are some tips to help you do that:

Use a Paper Bag

When storing fresh mushrooms, it is best to use a paper bag. This helps to absorb any excess moisture and prevent mould from growing. You can also place a paper towel at the bottom of the bag to absorb any additional moisture. This method is especially useful if you are storing pre-packaged mushrooms. Simply make a small hole in the original packaging, take out the required number of mushrooms, and then cover the opening with a sheet of paper.

Avoid Tightly Sealed Containers

Do not store mushrooms in tightly sealed containers with fitted lids as these can cause moisture build-up, leading to mould growth and discolouration. If you must use a container, opt for a plastic container with holes poked in the lid to allow airflow and prevent spoilage.

Store in the Fridge

Store fresh mushrooms in the refrigerator to prolong their shelf life. Place them in the fridge as soon as possible after purchasing to maintain freshness. Aim to use fresh mushrooms within 3 to 4 days of purchasing, as they can go bad in the fridge after 7 days.

Freeze for Long-Term Storage

If you want to store mushrooms for an extended period, consider freezing them. Before freezing, it is important to blanch or sauté the mushrooms to preserve their flavour, colour, and texture. You can also flash freeze them by spreading them on a baking sheet and placing them in the freezer. Once frozen, pack them into freezer bags or airtight containers.

Dry the Mushrooms

Drying mushrooms is another effective method for long-term storage. It removes moisture, inhibits bacterial growth, and prevents spoilage. You can use a food dehydrator or air-dry them. Once dried, store the mushrooms in an airtight container away from moisture, air, and light.

By following these storage tips, you can help prevent mushroom discolouration and enjoy fresh, tasty mushrooms for longer.

Freezing, drying, pickling, confiting, or smoking mushrooms

Mushrooms do tend to discolour after cutting, with one source citing a dull grey tint after frying or sauteeing with other ingredients. To prevent this, you can try salting them to draw out the moisture, or cut out the gills where most of the discolouration comes from. You could also try cooking the mushrooms separately and adding them to your dish at the end.

If you're looking to preserve your mushrooms, here are some methods you can try:

Freezing

Freezing mushrooms can be tricky because they are full of moisture, which crystallises and ruins the texture. One successful method is to cook the mushrooms first, and then freeze them. Some people have had success freezing sliced raw mushrooms in a bag for pizza toppings, but they must be cooked without thawing first.

Drying

To dry mushrooms, first, clean them with a damp paper towel or a mushroom brush, and then quickly rinse them under cold running water. Peel and slice large mushrooms, and leave small mushrooms whole and unpeeled. You can then dip them in a solution of one teaspoon (4 grams) of citric acid and one quart of water for 3-5 minutes. Drain them, and then arrange them in a single layer on drying trays. Dry at 140 degrees F (60°C) in an oven or dehydrator for 8-10 hours, turning large pieces over every 3-4 hours. They should be dry and leathery. Place the dried mushrooms in a container and store them in a cool, dry, dark place or in the refrigerator or freezer. They will last for 6-12 months.

Pickling

Pickled mushrooms are easy to make and can be stored in the refrigerator for several weeks. Clean and wash the mushrooms, and then put them in a pot and fill it with enough water to cover them. Add half a cup of vinegar, bring to a boil, and cook for 15 minutes. Drain the mushrooms, and then add water, salt, sugar, bay leaves, and peppercorns to a separate pot. Bring this to a boil, and then add 6 tablespoons of vinegar. Remove from the heat, and then clean and dice garlic into small pieces, placing them at the bottom of jars. Fill the jars with the cooked mushrooms, and then pour the marinade over them. Cover and store in the refrigerator.

Confit

Mushroom confit is a dish of slow-roasted mushrooms in olive oil with aromatics like garlic and fresh herbs, softened over a few hours in a low-heat oven. You can use any variety of mushrooms, but they should be roughly equal in size to ensure even cooking. Arrange the mushrooms in a single layer in a baking dish, and then pour the oil mixture over them, seasoning with salt and pepper. Toss to combine, and then roast in the oven until soft and tender, for about 2 hours. Let the confit cool, and then pack it into jars or storage containers, which can be stored in the refrigerator for up to one month.

Smoking

It is possible to smoke mushrooms, but it is not recommended due to the health risks involved. All smoke contains harmful toxins and particulates that can damage your lungs, and there is also the risk of inhaling mould spores.

Frequently asked questions