Ketchup Cup Agar: A Budget-Friendly Alternative for Mushroom Cultivation

Growing mushrooms at home is becoming increasingly popular, and you don’t need to spend a lot of money on fancy equipment. There are many everyday items that you can use in your cultivation journey.

One essential step in mushroom cultivation is agar, a nutritious substance that mycelium grows on. Agar is typically used to start spores or liquid culture (LC) in petri dishes. However, agar plates can get expensive if you're making a lot of them.

A cheaper alternative? Ketchup cups! I’ve been using this method for years with great success. You can get a pack of 100 ketchup cups for under $15, making it one of the most budget-friendly agar solutions available.

What You’ll Need

Here’s everything required to make your own ketchup cup agar plates:

• Ketchup cups with lids

• Agar powder

• Malt extract powder

• Digital scale

• Spores or liquid culture (LC)

• Still air box (SAB) or flow hood

• Mason jar or pressure cooker-safe bottle

• Distilled water

• Pressure cooker or large pot

• Sterile work environment (gloves, alcohol wipes, etc.)

Why Use Ketchup Cups for Agar?

• ✅ Affordable – 100 ketchup cups cost less than 10 petri dishes.

• ✅ Convenient – Pre-sterilized and disposable, no need to clean and reuse.

• ✅ Compact – Takes up less space in your still air box or incubator.

• ✅ Effective – Works just as well as traditional agar plates.

Step-by-Step: Making Ketchup Cup Agar

1. Prepare the Agar Mixture

1. Measure 250ml (1 cup) of distilled water and heat it in the microwave for about 2 minutes.

2. While the water is heating, weigh out:

   • 5g of agar powder

   • 7.5g of dry malt extract powder

3. Add the dry ingredients to a quart-sized Mason jar or any pressure cooker-safe bottle.

4. Once the water is heated, pour it into the jar.

5. If using a jar with a lid, ensure it has a filter patch to allow for gas exchange.

6. Swirl the mixture for 1-2 minutes until fully dissolved.

2. Sterilize the Agar

1. Place the jar in a pressure cooker (PC) or a large pot with a metal rack to keep it elevated above the water.

2. Pressure cook at 10-15 PSI for 20-30 minutes. (If using a regular pot, boil it for 30-40 minutes.)

3. After sterilization, let the agar cool slightly (but not solidify) before pouring.

3. Preparing the Ketchup Cups

1. Set up your still air box (SAB) or flow hood.

2. Stack clean ketchup cups and lids in one corner.

3. Once the agar is cool enough to handle but still liquid, start pouring.

4. Pouring the Agar into Ketchup Cups

1. Ensure your hands are clean (use rubbing alcohol or wear sterile gloves).

2. Pour a small amount of agar into each ketchup cup (about ⅓ full).

3. Immediately place the lid on each cup.

4. Allow the agar to fully cool and solidify.

How to Inoculate Ketchup Cup Agar Plates

1. Place your cooled agar-filled cups inside your still air box.

2. Remove the lid and add a few drops of spores or LC to the surface.

3. Secure the lid back on and label each cup.

4. Store them in a clean, warm area (~70-75°F) for colonization.

Final Thoughts

Using ketchup cups for agar is a simple, budget-friendly solution for mushroom cultivators. Whether you’re growing gourmet mushrooms or experimenting with new strains, this method can save you time and money.

👉 Looking for an even easier method? Check out my No-Pour Agar Guide to make agar without pouring — great for beginners or anyone trying to reduce contamination risk.