Basic Agar Technique

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Basic Agar Technique

Agar is a substance that is mixed with a nutrient to create whats called a medium. A lot of people will say, "Oh, I'm using agar to grow mushrooms".

That statement is wrong. There MUST BE a nutrient mixed in with the agar in order to use it. For example Malt Extract Agar. This is Malt Extract and Agar mixed together. Potato Dextrose Agar is Dextrose, a powdered potato powder and agar mixed together. There are literally thousands of different combinations with different things. There's chocolate agar, Sheeps blood agar, many different kinds of recipes.

Bacteriological grade agar is a base agar. A base agar is highly pure, extremely clean agar. It has NO NUTRIENTS. Bacteriological grade agar is generally used by those who want top of the line agar and who make their own agar recipes. Bacteriological grade agar WILL NOT grow ANYTHING by itself, it needs to have a nutrient added to it.

Beginners should use MEA (Malt Extract agar) or PDA (potato extract agar).

There are innumerable formulas for making agar to grow mushroom mycelium on. Here we will discuss the basics and let you experiment to develop your own favorite recipe for your favorite mushroom. Remember this mixture is designed as a rich food source for your mycelium to grow on and it will also support many other organisms. First you must have a recipe to follow. Let's keep it simple for our example. Of course ingredients can be added, deleted, or combined at different ratios. For many mushrooms malt based agar is sufficient.

For this ultra simple example we will use a 50 - 50 mixture of agar and malt extract.

To fill 20 Petri dishes we will need approximately 500ml of solution. We will need 10 grams of agar and 10 grams of malt extract mixed with 500ml water. An acceptable container is an ordinary quart jar with matching plastic lid and synthetic filter disc fitted inside the lid.

After stirring contents, loosely fit the lid with the filter disc fit inside the lid,

and secure the lid on the jar.

Place in pressure cooker and add 3000 ml water to the pressure cooker (less water should be used for smaller pressure cookers, achieving one inch of standing water on the side of the jar).

Sterilize for 30 to 45 minutes at 15 pounds pressure. NOTE: Make sure not to exceed this pressure or time frame or the sugars in the malt will caramelize thus promoting mutations or cottony growth, which is not a good thing.

After cooling and returning to normal pressure open sterilizer unit in front of a HEPA filtered air stream or remove jar into a clean and sterilized glove box.

As soon as jar is just cool enough to hold but while the contents are still molten, pour just enough in to each petri dish to cover the bottom. Fill all 20 dishes in the sleeve.

NOTE: With experience you will be able to do this filling process quickly. Open dishes for as short a time as you can and remember when you open a dish air will 'spill' in and potentially contaminate your agar before you even start so be careful.

Allow filled dishes to cool and solidify in the air stream. Once the agar is solid the plates can be stored or used. Seal dish edges with Parafilm.

The following is a C.O.A. (Certificate Of Analysis) for high grade, premium Bacteriological Grade Agars. A Bacteriological Grade Agar is recommended for uses concerning microbiological, mycological or any laboratory/research work that needs to have the absolute highest performance standards.

(Note: Food Grade Agar Works Fine. Try "Telephone Brand" or other agar at an Asian food store )

Bacteriological Grade Agar - Certificate of Analysis

Particle Size               -       80 - 140 Mesh

Moisture                    -        8,7%

Total Ash                   -       3,2%

Water Absorption         -       53,5 ml

Acid-Insoluble Ash        -       0,2%

To Pass ASTM 40 Mesh    -    100%

To Pass ASTM 60 Mesh    -    99.2%

To Pass ASTM 80 Mesh    -    95.4%

To Pass ASTM 100 Mesh   -   90.1%

To Pass ASTM 140 Mesh   -   26.5%

1,5% Agueous Solution:

Heated to boiling, kept the boiling conditions for 15 minutes, cooled to 60C

Heated to boiling, autoclaved at 121C for 15 minutes, cooled to 60 C

Viscosity (cps)   -   14.6 cps
(Brookfield-LVT # 1,60 rpm)

Viscosity (cps)   -   11.4 cps

Cooled to 50C

Absorbance at 430 nm -0.05

Absorbance at 430 nm - 0.05

Absorbance at 520 nm   -   0.04

Absorbance at 520 nm - 0.05

pH   -   7,11

pH - 5,85

Clarity (NTU)   -   8,2

Clarity (NTU)   -   7,4

Gel Strength (NIKKAN, 20C, 20")   -   920 gr/cm2

pH Gel   -   6.86

Gelling Point    -   35C

Melting Point   -   88C

Dyvalent Cations   -  220 ppm

Chlorine (NACL)  -  95 ppm

0.5% Agueus Solution: Heated to Boiling and Cooled to 40C


Heavy Metals - (As, Pb)   -  < 5 mg/kg

Lead                       -  N.D. < 2 mg/kg

Arsenic (As)             -  N.D. < 3 mg/kg

Bacteriological Tests:

Total Aerobic Mesophilic Bacteria - < 2000

Resistant Thermophilic Bacteria - Abs

Coliforms - Abs

Yeasts -  < 100

E. Coli - Absent

Salmonella - Absent

Molds - < 100

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