6 min read · published 2026-10-14
The no-pour agar tek sterilizes agar inside the cup it will be used in, which skips the step where hot media is poured into open dishes in front of a flow hood. The result is a sealed, ready-to-use plate that never passes through open air before inoculation.
The no-pour method
Traditional agar work involves cooking agar media in a flask, then pouring it into empty, pre-sterilized petri dishes inside a still-air box or flow hood. Every second the lid is off a dish is a window for contamination. The no-pour approach reverses the order: liquid agar goes into small containers first, the lids go on loosely, and the whole batch is pressure-cooked together. When the containers cool, the agar solidifies in place and the lids seal down. No pouring, no open-air exposure, no separate sterilization step for the dishes.
Choosing containers
Standard 90 mm petri dishes work, but the cheap option is the PP5 condiment cup, the kind restaurants use for ketchup. The 60 ml and 75 ml (2 and 2.5 oz) sizes hold enough agar surface for transfers and spore isolation while stacking neatly inside a pressure cooker. Polypropylene (the PP in PP5) tolerates pressure-cooker heat, which is why these cups survive sterilization where thinner takeaway plastics deform.
Silicone-lidded glass jars (60 ml or 120 ml) are another option. They cost more up front but last indefinitely and tolerate repeated pressure-cooker cycles without deforming.
The agar recipe
A standard malt extract agar (MEA) recipe for 250 ml of water uses 5 g of agar powder and 7.5 g of light malt extract (LME). Scaling up, 500 ml of water calls for 10 g agar and 15 g LME, and a full liter uses 20 g agar and 30 g LME. The agar powder provides the gelling agent while the malt extract supplies sugars that mycelium feeds on.
To mix, add the dry ingredients to the water in a heat-safe container and stir or swirl until dissolved. Some growers heat the water in a microwave for two minutes before adding the powders to speed dissolution. The liquid should be uniformly cloudy with no visible clumps before it goes into the containers.
Filling the containers
Pour or pipette the warm liquid agar into each cup, to a depth of about 2 cm. For a 75 ml (2.5 oz) condiment cup, that means about 20 to 25 ml of media per cup. Overfilling wastes media and can cause lids to stick shut under pressure. Underfilling leaves too thin a layer for mycelium to grow on.
Set the lids on top loosely. They should rest on the rim without being snapped shut. This allows steam to penetrate during sterilization and prevents pressure from blowing lids off or cracking containers.
Sterilization in the pressure cooker
Arrange the filled cups upright on a rack inside the pressure cooker. Stack them if needed, but avoid packing so tightly that steam cannot circulate. Bring the cooker to 15 PSI and hold it there for around 20 minutes, lowering the heat slightly once it reaches pressure. A fully packed cooker takes longer to heat through, so a crowded load needs a little extra time.
After the timer finishes, turn off the heat and let the pressure drop naturally. Do not release the valve manually. Rapid depressurization can cause the liquid agar to boil over inside the cups, making a mess and introducing contamination vectors. A natural cool-down takes 30 to 60 minutes depending on the cooker.
Cooling and sealing
A 1 percent agar solution stays liquid until it cools to about 32 to 39 degrees Celsius and then sets into a gel that will not melt again below 85 degrees. The cups can be left inside the sealed cooker during this phase. Some growers remove the cups once pressure has equalized and set them on a clean surface in front of a flow hood or inside a still-air box. The goal is to let them cool with lids resting in place until the agar solidifies, then snap or press the lids down firmly.
Condensation on the inside of the lid is a recurring problem with no-pour plates. Excess water droplets can pool on the agar surface and promote bacterial growth. To reduce condensation, let the cups cool upright first until the agar has just set, then flip them upside down for storage. Gravity pulls the condensation to the lid (now on the bottom), keeping the agar surface dry.
Storing no-pour plates
Sealed no-pour plates stored in a clean, room-temperature environment remain viable for weeks to months. Wrapping stacks of cups in cling film or placing them in sealed zip-lock bags adds another barrier against airborne contaminants. Refrigeration at 4 degrees Celsius extends shelf life further, though some color change in the agar is normal after prolonged cold storage.
Label each batch with the date, media type, and any additives (such as activated charcoal or antibiotics). Running through a stack of 50 or more cups in a single pressure-cooker session means plenty of plates are on hand when transfers or isolations come up, which is one of the main practical advantages of the no-pour approach.
Advantages for beginners
The traditional pour method demands either a flow hood or fast, practiced movements inside a still-air box. Neither is forgiving for someone learning sterile technique for the first time. No-pour agar removes the riskiest step from the process. The media goes from pressure cooker to sealed container without being exposed to room air at the stage when it is most vulnerable.
The cost per plate is also lower, since a condiment cup costs a fraction of a petri dish and the agar and LME stretch across hundreds of plates. That makes it practical to attempt transfers, clone tissue samples, or isolate sectors from multispore germination without worrying about wasting expensive petri dishes on beginner mistakes.
Adapting the recipe
Growers modify the base MEA recipe for specific purposes. A little nutritional yeast adds nitrogen. A small amount of activated charcoal darkens the agar, making white mycelium easier to see against the surface. Antibiotic additives like gentamicin (added after sterilization, once the agar cools to around 50 degrees Celsius) suppress bacterial contamination when working with outdoor tissue samples.
Potato dextrose agar (PDA) is another common base: 200 g of diced potato boiled in 1 liter of water, strained, then combined with 20 g of dextrose and 20 g of agar. The no-pour method works identically with PDA or any other agar-based medium. The only requirement is that the medium is still liquid when it goes into the containers.
A 250 ml batch of MEA fills roughly 10 to 12 condiment cups, meaning a single pressure-cooker load can produce 40 or more plates when scaled to a full liter.