What is an Agar Dish?
An agar dish is a growth medium used in laboratories to culture small organisms. This same technique is used by hobbyists to grow mycelium. The agar dish contains nutrients in a solid gela tinous form that allows mycelium to grow faster.
What is the purpose of using agar dishes?
Well, the first reason we use agar dishes is to provide every chance for a starting culture to succeed. The medium in the dish is a sterile environment fully reserved for the mycelium. It is like an all-you can-eat buffet every day.
The second reason the hobbyist uses an agar dish is to test a syringe of live culture. Before using a live culture on grain jars, or before making ten or more dishes from a liquid culture, it is in fact good practice to make only one or two dishes with that liquid culture and then wait a week. This method is used in order to know and see if a liquid culture is clean or contaminated. If the culture is not clean, then the hobbyist will clearly see the contamination and no more resources, and time will be spent on a contaminated liquid culture.
Once the hobbyist is satisfied with the mycelium developed in a dish, more options present themselves.
The agar with mycelium can be cut into pieces using a sterilized scalpel and transferred into multiple agar dishes, which allows for the multiplication of good mycelium and creating backups.
The agar with mycelium can also be placed into grain jars. This also allows for the multiplication of the mycelium, but on grains that can later on be used to inoculate wheat straw or sawdust, which takes the hobbyist one step closer to producing actual fruit body. In theory, grains are used to make more grains or to inoculate bags, but it is possible to use grains on agar dishes, or to create liquid culture, but the risk of contamination is much higher.
The agar can also be cut into pieces and turned into liquid culture, which can then be used to create agar dishes, inoculate grains or create more liquid culture.
Ideally, a waiting time of two to four weeks, depending on the strand or mycelium, before using an agar dish is about right. This allows for mycelium to expand on agar, and also allows contamination to show. Contamination is usually visible after a few days, but if after a week there is no contamination, chances are there will be no contamination in that dish.
Preparing agar is a straightforward process. There are many recipes on the internet, on forums and Facebook groups, so we are not going to provide agar recipes, simply because it is a matter of personal preference and depends on the items we have at hand. The recipes that most people use are based on water, dextrose and malt, but again, it is a simple matter of personal preference and what the hobbyist has on hand. Some boil potatoes and use that water as the basis for preparing an agar dish. We prefer to stick with water, malt and dextrose. like a lot of aspects of this hobby, this is a matter of what best works for you.
Once a recipe is chosen by the hobbyist, it must be prepared in a jar. When preparing liquids, it is important not to go beyond 50% capacity, because once that jar goes into the pressure cooker, the liquid content will boil violently and will have the tendency to come out of the jar and spill in the pressure cooker, which in turn will contaminate other things we have in the pressure cooker.
In addition, the hobbyist should never completely tighten the lid. We want to allow steam to escape from the jar; otherwise, the jar may crack or simply explode in the pressure cooker due to steam buildup in the jar. The hobbyist should cover the jar lid with aluminium foil before putting it in the pressure cooker. This will stop excess water or steam from getting into the jars, and change the content that was prepared.
From this point on, the jar goes into the pressure cooker for 30 minutes at 90 PSI. It’s important to start counting once the pressure cooker hits 15 PSI.
Once the pressure cooker can be opened, the hobbyist takes the jars out to allow them to cool down. If the agar is poured into dishes when hot, there will be a lot of condensation in the dish, which is basically excess moisture, and in turn could result in contamination. Therefor, the hobbyist must allow the agar to cool down, but not too much; otherwise, the agar will solidify in the jar and become useless.
Stacking the dishes on top of each other will reduce condensation.
After the agar dish is prepared and cooled at room temperature, it can be sealed and kept in storage. The correct product to seal dishes is called parafilm. Some hobbyists use electrical tape, but Parafilm is the product for sealing dishes. It’s important not to use parafilm on hot dishes; since Parafilm is a type of wax, it melts and becomes difficult to remove later on.
Allowing the dish to sit for few days will allow the hobbyist to detect contaminated dishes, and not spend time and resources on them, and simply discard them and use the ones that are free of contamination.
Another method of preparing agar is the “no pour” agar, which consists of pouring the agar directly into small 125ml jars. These jars then go into the pressure cooker and get sterilized. It is no longer required to pour agar after sterilization, which could become contaminated while pouring. We still prefer to pour sterilized agar into glass dishes.
The agar is made in a larger 1L jar and then poured into the smaller 125ml jars, which is the same process as a Petri dish, except that every small jar will end up in the pressure cooker and get sterilized.
Please see our other blogs covering more specific subjects about the fun world of growing mushrooms.