Grain jars not colonising: wet spot and bacterial contamination

A jar that isn’t moving is not always contaminated. A jar that isn’t moving and smells sour when you open it is, and the smell is the diagnostic that matters — bacteria announce themselves in a way that molds don’t.

Do not open a suspect jar to check unless you’ve decided you’re prepared to throw it out. Once you break the seal you can’t unbreak it.

What you’re looking at

Wet spot shows as grey to grey-brown patches in the grain, wetter and glossier than the kernels around them. The grains in the patch clump into a gluey mass rather than staying loose. Your mycelium advances toward it and then simply stops, leaving a clean line where the two meet.

The smell is the confirmation: sour, sharp, like fermenting apples or a neglected dishcloth. Healthy colonising grain smells faintly of mushroom and bread. If your reaction to opening the jar is to pull your head back, that’s wet spot.

Bacillus forms endospores that survive normal boiling. That’s the entire reason grain needs a pressure cooker and straw doesn’t.

Telling it apart from a jar that’s just slow

Three things are commonly mistaken for contamination:

Grain that’s too dry. Under-hydrated grain colonises slowly and unevenly and looks stalled. It smells of nothing. The fix is prevention next time — hydrate to field capacity before sterilising.

A cold room. Below about 65°F most cultivated species crawl. The mycelium looks healthy, just barely moving. Warm the room and it resumes.

A slow or tired culture. Repeatedly transferred cultures lose vigour. The growth is even and white, just unhurried.

None of those smell sour. The smell is the line.

Can it be saved?

No. Not with grain, not ever.

Grain is nutrient-dense and enclosed, which is exactly the environment Bacillus wants. There is no treatment that reaches the interior of a jar, and there’s no version of this where you separate the good grain from the bad — the bacteria are throughout the substrate well before the discoloured patch is visible.

Spawning contaminated grain to bulk transfers the bacteria to the bulk, where they will do the same thing on a larger scale.

Getting it out safely

Wet spot doesn’t aerosolise the way a sporulating mold does, so this is less fraught than disposing of Trichoderma. Still:

1. Keep the lid on. Take the jar outside before opening it.
2. Empty it into the trash, not the compost, and not near your grow space.
3. Wash the jar in hot soapy water, then run it through a sterilisation cycle before reusing it.
4. Wash your hands before touching other jars.

What caused it

In rough order of likelihood:

The pressure cooker didn’t do its job. This is the cause most of the time. Grain needs 15 psi for 90–120 minutes, and the clock starts when the gauge reaches 15 psi, not when you turn the burner on. Common failures:

• Timing from the moment the stove went on
• A jiggler valve that never settled into a steady rhythm
• Jars packed so tightly that steam couldn’t circulate
• Running at 10 psi because that’s where the gauge sat

Grain too wet. Excess free water in the jar gives bacteria a medium to move through. After hydrating, grain should be dry to the touch on the outside of each kernel — no water pooling in the bottom of the jar, ever. If you can tip the jar and see liquid move, it’s too wet.

Cracked or damaged kernels. Split grains release starch into the free water and give bacteria an easy start. Rinse and skim floaters before hydrating.

Contamination at inoculation. Less common for Bacillus specifically, since it usually arrives inside the grain rather than through the air, but a compromised filter patch or a badly-sealed lid lets it in later.

Old grain. Grain stored warm and damp arrives with a higher spore load than grain that’s been kept dry and cool.

Preventing the next one

The pattern: wet spot is a sterilisation failure, not a technique failure. If you’re getting it repeatedly, the pressure cooker is where to look before anything else.

• Time from pressure, not from heat. Set the timer when the gauge holds 15 psi.
• 90 minutes for pint jars, 120 for quarts. Longer doesn’t hurt.
• Leave space between jars for steam to move.
• Hydrate to field capacity, then let the grain surface-dry before jarring.
• Add a little gypsum at around 5% of dry weight — it keeps kernels separate and buffers pH.

If several jars from one cook go down, suspect the cook. If one jar out of twelve goes down, suspect that jar’s lid or filter.

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Sour smell, gluey grey patches, mycelium stopping at a clean line. Three things, all pointing the same way. Bin it and check your pressure cooker.