Mushroom

MATURITY & QUALITY

Maturity Indices

Agaricus bisporus mushrooms (Button Mushrooms) are harvested by maturity and not by size. Maturity is reached when the caps are well- rounded and the partial veil is completely intact. The stipe (stalk) should have a small length to thickness ratio. Stipe length should be sufficient to permit some trimming without cutting flush to the veil.

Quality Indices

Good quality, fresh ‘Agaricus’ mushrooms should be white to dark brown. White forms are most prevalent. Uniform, well rounded cap with a smooth glossy surface and fully intact veil are indicators of best quality. Stipes are straight and glossy in appearance with an even cut edge. Cleanliness (minimal growth medium residue) and absence of browning or other discoloration are additional quality factors. Visible, open gills and absence of a stipe are negative factors.

U.S. grades are No. 1 and No. 2. Sizes range from Small {Button} (1.9 – 3.2cm / .75 – 1.25 in.), Medium (3.2 – 4.5cm / 1/25 – 1.75 in.), to Large (4.5 cm / 1.75 in. and larger) measured as cap diameter. Grades discriminate for maturity, shape uniformity, cleanliness and trim quality.

TEMPERATURE & CONTROLLED ATMOSPHERE (CA)

Optimum Temperature

0° – 1.5°C ( 32° – 35°F ) Storage life is typically 5-7 days at 1.5°C (35°F) and 2 days at 4.5°C (40°F).

Optimum Relative Humidity

95-98%; High relative humidity is essential to prevent desiccation and loss of glossiness. Drying is correlated with blackening of the stipe and gills and curling of the cap. Commonly mushrooms are packed and shipped in cartons with a perforated overwrap to maintain high humidity.

Rates of Respiration

To calculate heat production multiply ml CO₂/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day. NA= not applicable

Rates of Ethylene Production

>0.1µl/kg·hr at 20°C (68°F)

Responses to Ethylene

Agaricus mushrooms are not significantly impacted by exogenous ethylene.

Responses to Controlled Atmospheres (CA)

Extended storage (~12-15 days) in 3% O₂ and 10% CO₂ at 0°C has been Controlled demonstrated. Elevated CO₂ at 10-15 % (typically 10%) in air is beneficial in Atmosphere (CA) preventing decay and reducing the rate of blackening of the stipe and gills. The beneficial effect is most pronounced if temperatures cannot be maintained below 5°C (41°F). Short exposure to higher CO₂ concentrations (20%) is safe and beneficial only if temperatures can be maintained at 0° – 1°C (32° – 34°F).

Improper control of controlled atmospheres or improper packaging can rapidly lead to depletion of oxygen resulting in conditions favorable for Clostridium botulinum. For this reason, primarily, the use of CA and MA is not common.