Mushroom facts

Everything you wanted to know about mushrooms

The varieties grown in New Zealand, why they're so good for you, and the fascinating journey from straw to punnet.

Know your mushrooms

Types of mushroom

White button, Swiss brown and portobello mushrooms are the everyday varieties grown in New Zealand. Exotic kinds — shiitake, oyster and enoki — bring their own textures and flavours.

White button mushrooms

White button

Also known as: Button

Looks
White to beige caps that vary in size, with the veil still closed.
Flavour
Delicate, and stronger when cooked.
Best for
Very versatile, fresh or cooked: salads, kebabs, soups and stir-fries.
Swiss brown mushrooms

Swiss brown

Also known as: Gourmet, crimini or brown button

Looks
A naturally darker cap, from light tan to rich brown. Firmer flesh and less shrinkage when cooked.
Flavour
Slightly nutty and more intense than white buttons.
Best for
Swap in for white mushrooms when you want a fuller flavour. Great marinated or in kebabs.
Portobello mushrooms

Portobello

Also known as: Brown flat or field

Looks
Medium to large brown mushroom with an open tan cap and gills showing.
Flavour
Deep, rich and meaty.
Best for
Whole or sliced, grilled, baked or stuffed. Brilliant on the BBQ or as a burger ‘patty’.
Shiitake mushrooms

Shiitake

Also known as: Exotic

Looks
Native to Asia, where it grows naturally on trees in forests. In NZ it's grown on logs and blocks.
Flavour
Rich, textured and smoky, packed with umami.
Best for
Stir-fries, broths and noodle soups such as pho, risotto and roasts.
Oyster mushrooms

Oyster

Also known as: Exotic

Looks
Fan-shaped caps in grey, blue, yellow, pink or white, with tender, tasty stems.
Flavour
Subtle and sweet, with a light, fruity aroma.
Best for
Tear and pan-fry until golden, or add to soups, pasta and stir-fries.
Enoki mushrooms

Enoki

Also known as: Enokitake (Flammulina velutipes)

Looks
Long, slender white stems with tiny caps, highly regarded in Japan.
Flavour
Mild and sweet with a pleasant crunch.
Best for
Hot pots, ramen, salads and quick stir-fries. Add at the end of cooking.

Nutrition

Small mushroom, big goodness

Mushrooms are low in fat and carbohydrate, high in potassium and low in sodium, and an important source of B-group vitamins and the trace mineral selenium. That makes them especially valuable for vegetarians.

A New Zealand analysis by Crop & Food Research found mushrooms to be:

  • Low in fat and therefore calories
  • Low in carbohydrate, most of which is fibre
  • A moderate source of protein
  • High in potassium but low in sodium, a desirable balance for a healthy diet
  • A significant source of selenium
  • A good to excellent source of some B-group vitamins, including riboflavin (B2) and niacin (B3)
~380 mgPotassium per 100 g. Potassium helps maintain normal heart rhythm, fluid balance and muscle function.
~⅓ RDISelenium from a 68 g serve in the NZ analysis, thanks to the straw and chicken-manure compost.
~25% RDIRiboflavin (vitamin B2) per 68 g serve. It helps turn food into energy.
2–3 mgNiacin (B3) per 100 g, while most vegetables contain under 1 mg.

Source: Nutritional quality of mushrooms, Dr Carolyn Lister, New Zealand Institute for Crop & Food Research, December 2003. RDI = recommended daily intake at the time of the study. Figures are indicative. For dietary advice, talk to a health professional.

How mushrooms are grown

Why do you never see a wide open field of mushrooms?

Mushrooms don't need light to grow. They get all their goodness from the rich compost they grow in, so farmed mushrooms are grown indoors and are available all year round.

Growing them is part science, part craft. Here's the journey from a bale of straw to the punnet in your trolley.

A low view along a bed of white button mushrooms under the growing racks at Quality Mushrooms

Step 1: Straw wet-down and composting

Good-quality wheat straw is wetted over several days, then a protein source (often chicken litter) and gypsum are added.

  • Gypsum keeps the compost open, and the protein speeds up natural microbial activity.
  • Temperatures reach up to 84 °C, ‘cooking’ and caramelising the straw.
  • Over 9–14 days it is turned and aerated until dry straw becomes dark, even compost.
A Quality Mushrooms worker in hi-vis operating a compost turner, with steam rising from the compost

Step 2: Pasteurisation and conditioning

The compost moves into a specially insulated room with powerful fans and under-floor air. Again, it's a natural process driven by micro-organisms.

  • Even-up: about 12–16 hours to reach 54 °C or more.
  • Pasteurisation: 57–62 °C for 5–7 hours to knock out unwanted spores, fungi and pests.
  • Conditioning: 4–5 days stepping down to 45–46 °C, then cooling to about 30 °C.
Steaming mushroom compost being turned at Quality Mushrooms

Step 3: Spawning

The finished compost is mixed with mushroom spawn of the grower's chosen strain, often with a slow-release supplement.

  • Mycelium ‘runs’ through the compost at around 25–28 °C with high CO₂.
  • Growers use bulk spawn-run rooms, long shelves stacked 5–6 high, large wooden boxes or bags.
A long bed of white button mushrooms under the growing racks at Quality Mushrooms

Step 4: Casing and flushing

Once the compost is fully colonised, a 40–50 mm layer of wet peat and lime ‘casing’ goes on top and is kept moist for about a week.

  • Fresh air is introduced, and CO₂, humidity and temperature are carefully adjusted.
  • Tiny pinheads form and grow into buttons and browns.
  • Mushrooms come in ‘flushes’ about 7–10 days apart, usually 3–4 flushes over 4–6 weeks.
An aisle in a Quality Mushrooms growing shed, with brown mushrooms on the left shelves, white on the right, and packed boxes stacked alongside

Step 5: Harvesting

Every mushroom is picked by hand. White mushrooms are usually picked as tight buttons, sometimes several times a day for the best quality.

  • Brown mushrooms are generally picked as flats or portobellos.
  • Beds are tidied and re-wetted between flushes.
  • Mushrooms are packed and chilled straight away to lock in freshness.
A Quality Mushrooms picker in a blue coat harvesting white button mushrooms between the growing shelves

Step 6: Grading and packing

Freshly picked mushrooms are cooled straight away, then graded and packed into punnets and cartons in a temperature-controlled room.

  • Quality checks happen at every stage, from bed to punnet.
  • Packed mushrooms stay chilled all the way to the shop.
  • Most reach supermarket shelves within a day or two of picking.
A 400 g punnet of Quality Mushrooms white buttons

Growing process adapted from the Federation's grower guide. Photos from Quality Mushrooms (Ōhaupō) and Out of the Dark Mushrooms.

FAQs

Common questions

Why do you never see a wide open field of mushrooms?

Because mushrooms don't need light to grow. They get all their nutrients from the compost they grow in, so commercial mushrooms are grown indoors in climate-controlled rooms and are available all year round.

Are mushrooms a vegetable?

Mushrooms are fungi, not plants, but in the kitchen they're used like a vegetable. They're low in fat and a source of B vitamins, potassium and selenium.

How should I store fresh mushrooms?

Keep them in the fridge, in their original packaging or a paper bag, and use them within a few days for the best flavour and texture.

What are mushrooms grown on?

In New Zealand, button and brown mushrooms are grown on compost made from wheat straw, chicken manure, gypsum and water, topped with a layer of peat and lime. Exotic varieties such as shiitake are grown on logs or blocks.

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