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Oven-Bag Pasteurization Pictorial

A great way for the pasteurization of straw/compost/dung.

This method was first brought to my attention by our fellow member, 6Tango. It is a great way for the pasteurization of straw/compost/dung. I have noticed that unlike the conventional method of "cooking" your bulk substrates in a pillowcase submerged in water, there is no strong odor, no loss of nutrients and no excess water drainage. The best is that you will not have to wait a few days to inoculate, due to the time for your pillowcase to drain all its excess water!!

When you pasteurize your straw/compost/dung in submerged water, you will notice that the resulting water is brown. This is most of the nitrogen and other nutrients which are flushed out from the substrate, not to mention your pot is pretty dirty and brown afterwards.

So here is the full pictorial of how using an oven-bag, and baking your compost/straw/dung in the oven to achieve full pasteurization.

Oven, oven safe bags, bulk substrate, water, tape (or string), meat thermometer.


1) You will first want to pre-heat your oven to about 300F.

Here is a picture of the oven bag. You might want to get that ready!

2) Next, load your oven bag with the desired amount of bulk substrate. In this pictorial I will be using the ©MycotaPro compost. It is comprised of aged cow dung, wheat straw, barley and other cool things. Make sure that your straw/compost/dung has been thoroughly dried before loading. This gets rid of some of the harmful bacteria, and is more likely to achieve full pasteurization.

Now if you wish, or if you have very fine compost, (like the MycotaPro compost) you will want to add some vermiculite. I dont believe it will be wanted with wheat straw. It is basically there to hold a little more water within the substrate, as well as keeping it fluffier and less dense. You can add 10%-30% vermiculite. Its also a good way to add volume to your bulk substrate.

3) Next, it is time to add water to your substrate. What is great about using oven bags, is that you will not have excess water from submerging a pillowcase into water. You will only add the amount of water that you need. However, it is recommended that you add tad bit more water due the evaporation during the baking time.

Water is the key ingredient into your substrate. You will want enough to keep it hydrated through a few flushes, yet, you do not want it overly wet so it doesn't cause any sort of contamination. As noted in "The Mushroom Cultivator" by Paul Stamets, a "field consistency" is the optimum water ratio into the substrate. It is a little more wet than damp. When you take a handful of the substrate, and you squeeze your fist as hard as you can, and a little trickle of water runs out of your fingers, you know you have added enough water.

Here is the consistency you are looking for:

4) Now that you have your straw/compost/dung all hydrated, all you need to do now is to tie off the top of the oven bag and then place a thermometer through the top, like so:


During the baking process, you will need to attend to your oven to check the thermometer for about the first hour. It is very important that you do not allow the temperature inside the bag to get above 185F! Once your thermometer has reached the temperature of about 170-180, turn down the oven to about 190-200F.

Due to the fact that this is dry heat, and the process of pasteurization will be slightly slower, you will need to bake your bag for about 2-3 hours. I would recommend 3 hours, and 2 if you are really restricted on time.

After your 3 hours are up, you will want to carefully (with oven mitts) take the bag out of the oven, take out the thermometer and tie off the top completely. Allow to cool for about 6-10 hours, or however long it takes for your bag to cool down. Once it is cool, you are able to get back to work and spawn with grain or grinded BRF cakes! No waiting 3 days for the water to drip out of your pillowcase!

As this is a work in progress, I encourage any questions you may have.

LOL........... after AngryS mentions my name. I gotta say something.

I believe the bags he appears to be using are high quality "autoclave" bags, about 5 liter in size . However, an oven bag will work fine, if handled carefully.

You can also "skin the cat" two (2) other ways:

If (BIG IF), if you have filter/patch bags....... or if you have plain autoclave bags, or oven bags.....and............. (BIG AND)..............

you have either milipore (micro/porious) surgical tape (which WILL withstand autoclave temps).....or transpore (micro/porious) surgical tape (which will NOT withstand autoclave temps). Either of which you can find at top notch medical supply stores.

You can load a bag(s) (as AngryS shows), then PC it for 90 minutes (unsealed, with the top folded over & held in place & closed with two (2) rubber bands.

Then allow the bag(s) to cool over/night in the PC (without opening it).
The following day, have grated cakes, or WBS jars ready to use as spawn. If using jars, spray the outside of them with lysol (to make sure the outside is clean of contam's), then spoon out a quart jar (or 2) into a bag, then squish it around to mix the spawn into the substrate, throughly.
If filter/patch bags (?), seal with an impulse sealer.
If not (?). Cut a slit a half inch wide, 3 inches long & remove the center, at the top of the bag, cover the slit BOTH inside & out with transpore or milipore tape (you just created a filter/patch), then tape the bag closed (with the same tape), or seal with an impulse sealer (if you have one handy).
Then, drop the bag(s) in a cardboard box, place the box in a safe, dark place arounf 80 to 84 F.......... AND LEAVE IT ALONE FOR A WEEK.
Don't take it out, to handle, fondle, breath all over it & eyeball, like it was something you want to have immediate sex with.

A watched pot ...... doesn' boil quickly...................
Nor, does fondling a green apple make it turn red & ripe.......faster

Here is an example of a couple PC'ed bags, left alone for a week.
They happen to be filter/patch, but are sealed with Transpore tape (just testing it).

After ther bags are fully colonized, dump into a CLEAN tray, squish flat & cover the tray with loose tinfoil & reincubate for about 3 days (so the substrate can knit back togather). Then, add casing mixture over the top, let it colonize a bit (until a good spread of mys crops out), then throw it in a fruiting chamber & initiate pinning.

6T (aka Mycota)

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