How to Test Liquid Culture (LC) on Agar: A Simple Guide for Growers

Liquid culture (LC) can be an incredibly fast and reliable way to expand your favorite fungi, but only if it’s clean. A contaminated LC can spread bacteria or mold into every grain bag you touch — which is why testing liquid culture on agar is one of the smartest steps you can take.

Whether you're brand new or experienced, this guide will walk you through why, when, and how to test LC on agar plates so you can tell if your liquid culture is clean or contaminated before it ever touches grain.

Why Test LC on Agar?

Even a crystal-clear liquid culture can hide contamination. An agar plate gives you a flat, controlled surface that makes it easy to spot hidden bacteria, mold, or yeast long before it reaches your grains or substrate.

Here’s what an LC agar test helps you catch:

• Bacteria – shiny, wet, or greasy-looking colonies
• Mold – usually fast, fuzzy, or pigmented growth
• Yeast – creamy, pasty, or dull colonies

A single LC contamination test on agar can save an entire batch of grain bags, time, and money.

What You’ll Need

You don’t need a lab to test mushroom liquid culture — just a simple, clean setup and a few reliable tools.

• Agar plates – Standard nutrient recipes like MEA, MYA, or SYA work great for LC testing. You can browse all pre-poured options in our Agar Plates Collection.
• Your liquid culture (LC) – store-bought, homemade, or gifted
• Sterile 10 cc syringe (with or without needle)
• Clean workspace – a still air box (SAB) or flow hood
• Gloves, 70% isopropyl alcohol, and paper towels

Step-by-Step: How to Test LC on Agar Plates

1. Prepare Your Workspace

Start by wiping everything down with 70% isopropyl alcohol — your SAB, working surface, and any tools you’ll be using. Let your still air box settle for a few minutes, or let your flow hood run so you have consistent, clean airflow. Position your plates and LC so you aren’t reaching over them during the process.

2. Label Your Plates

Before opening anything, label each agar plate with:

• LC name or batch ID
• Date
• “LC Test”

Good labeling makes it easier to compare plates, track batches, and spot patterns over time.

3. Open the Plate Carefully

Use the classic clam-shell technique: hold the plate in one hand and gently lift the lid just enough to work, keeping it angled downward. Avoid fully removing the lid — the goal is to minimize exposure to open air while you test your liquid culture.

4. Add a Small Drop of LC

This is where a lot of people overdo it. When you test LC on agar, you only need a tiny drop.

• If using the syringe with a needle attached, gently push out the smallest drop you can.
• For better control, remove the needle and lightly squeeze the sides of the syringe barrel — this makes it easier to release a single clean drop onto the agar without flooding the plate.

Too much LC can run across the agar surface and hide early signs of contamination, making it harder to tell if your liquid culture is truly clean.

5. Close and Seal the Plate

Once you’ve added your drop of LC, close the lid and seal the edges for better stability and protection during incubation.

You can wrap your plate using:

• Parafilm – the classic lab sealing film used for agar plates.
• Laboratory Polyfilm – a budget-friendly alternative that works extremely well.

Both options help prevent drafts, limit exposure, and keep your results clean and consistent while your LC test incubates.

6. Incubate the Plate

Store your plates.

Ideal temperature range: 68°F–74°F. Keep your plates in a dim, stable place away from direct light and heat sources.

7. Observe the Growth

Most LC tests will start showing growth within 24–72 hours, depending on the species and temperature. This is where you can clearly see whether you have a clean liquid culture or a contaminated one.

Signs of a clean LC on agar:

• Bright white mycelial growth
• Smooth, controlled, circular expansion from the inoculation point
• No strange colors, wet halos, or greasy spots

Signs of a contaminated LC:

• Greasy or wet-looking bacterial spots
• Fast, fuzzy, or colorful mold growth
• Yellow or brown discoloration around the drop
• Growth appearing in random areas away from the inoculation point

How Many Plates Should You Test?

Using just one plate can give you a false sense of security if contamination doesn’t happen to land on that specific plate. For a more reliable LC sterility test, it’s a good idea to use two to three agar plates per batch of liquid culture.

That way, if one plate looks good but another shows contamination, you’ll know the LC is not fully clean.

What to Do After Testing Your Liquid Culture

If the LC Is Clean

If your plates show strong, white, consistent mycelial growth with no odd colors or slime, you can confidently move forward. A clean LC can be used on:

• Grain bags or jars
• More agar work (transfers, expansion)
• Long-term storage methods

If the LC Shows Contamination

If you see clear signs of contamination, it’s best to treat that LC as dirty:

• Discard the LC rather than risking multiple bags
• Retest if you want to confirm the result
• If the LC was purchased, reach out to the vendor with photos of your plates

Advanced growers may sometimes transfer a clean leading edge from the plate and rescue the culture, but for beginners, it’s usually easier and safer to start fresh.

Final Tips for Reliable LC Testing

• Always test new liquid culture on agar before using it on grain.
• Remember: clear LC does not always mean clean LC.
• Avoid low-nutrient agar when testing LC — bacteria are easier to see on richer recipes like MEA, MYA, or SYA.
• Keep simple notes on each LC batch and how it tested.
• When in doubt, test again on fresh agar plates.

Recommended Agar Plates for LC Testing

If you’re ready to start testing your liquid culture, we offer a range of pre-poured plates that make the process fast and beginner-friendly:

• Light Malt Extract Agar (MEA) – Pre-Poured Plates
• Malt Yeast Agar (MYA) – Pre-Poured Plates
• Sorghum Yeast Agar (SYA) – Pre-Poured Plates
• Or browse all options in our Agar Plates Collection.

 

 

LC on Agar – Frequently Asked Questions

How long does it take LC to show growth on agar?

Most clean LCs will show visible mycelial growth within 24–72 hours, depending on strain and temperature. Some slower species may take a bit longer.

Can I test LC on low-nutrient agar?

You can, but it’s not ideal for spotting bacteria. For LC contamination tests, richer recipes like MEA, MYA, or SYA usually make contaminants easier to see.

Do I need a flow hood to test LC on agar?

No. Many growers successfully test LC using a still air box (SAB). A flow hood is nice to have, but not required for basic LC-to-agar testing.

How many agar plates should I use to test one LC?

Using 2–3 plates per LC batch gives more reliable results than just one plate and reduces the chances of missing contamination.

Is my LC bad if it looks clear?

Not necessarily, but also not guaranteed clean. Clear LC can still be contaminated. That’s why testing liquid culture on agar is so important before moving to grain.

Ready to test your LC? Grab pre-poured plates from our Agar Plates Collection and start building a clean, reliable workflow today.