Sterilizer Load Calculator

Plan loads before you light the burner, not after.

Loads = bags in the batch ÷ bags that fit per load, rounded up. A barrel steamer only sterilizes what physically fits inside it in one cycle, and every cycle costs the same fixed overhead — come-up time and cool-down — whether it's packed full or half empty. This tool takes your barrel size, your block weight, and your batch size, and tells you how many loads you're actually running and how long the whole batch will take, so you can plan a sterilizing day instead of discovering at 9pm that you need a third cycle.

Everything runs client-side. Nothing is stored, nothing is sent — change any input and the result updates live.

Capacity, bags per load, and cycle time.

Capacity: gallons to pounds of substrate

Barrel makers publish surprisingly little in the way of hard specs — I could not confirm Bubba's Barrels' own load figures directly, and no source anywhere publishes propane or water use for these rigs. What circulates among growers are secondary, word-of-mouth numbers: roughly 200 lb of blocks in a 55 gallon barrel, and roughly 300 lb in an 85 gallon barrel. That works out to about 3.6 lb of finished substrate per gallon of barrel volume, which is the ratio this calculator uses to scale to 100, 150, or a custom barrel. Treat it as a planning starting point, not a spec sheet — weigh a real load in your rig once and you'll know your actual number.

Cycle time: hold + come-up + cool

Every cycle has three phases: come-up (the barrel and its contents climb to temperature), hold (the temperature that actually kills contaminants is sustained), and cool-down (safe enough to open and unload). The hold time is the one number you should treat as most provisional and most important — this tool auto-fills a typical default by method but makes it fully editable, because your load size, packing density, and burner all change how long a true hold actually needs to be. Come-up and cool overhead are typically shorter for pressure cooking (higher differential drives faster heating, and pressure vessels vent down faster) than for atmospheric steam.

When the standard number is wrong.

These capacities and cycle times are typical, not gospel — barrel makers publish surprisingly little, and I could not confirm Bubba's Barrels' own specs directly. Treat every output above as a planning starting point and verify it against your actual rig.

The hold clock starts at the core, not the barrel

Atmospheric steam only sterilizes once the bag core reaches roughly 210°F and holds there — a short hold timed from when the barrel itself comes up to temperature can leave the center of a tightly packed load still cold, and that load comes out contaminated days later. Time the hold from when the core is confirmed up to temperature, not the chamber. A data-logging probe pushed into a center bag on a full load pays for itself the first time it saves a batch.

Supplemented substrate needs sterilization, not pasteurization

Bran- or soy-hull-supplemented sawdust must be fully sterilized, not just pasteurized — the extra nitrogen that makes supplemented blocks so productive is exactly what gives any surviving contaminant, especially Trichoderma, a massive head start if the kill isn't complete. Atmospheric barrels run long holds precisely because they're capped near 212°F (100°C) at sea level and can't push past it the way a pressure vessel can — the only lever atmospheric steam has is time.

Propane and water aren't published — meter your own first cycle

Nobody publishes propane or water consumption for these barrel rigs, and it genuinely varies with insulation, ambient temperature, wind, and burner output — a bare steel barrel in a Vermont winter and an insulated one in Georgia summer are different machines. This tool won't invent a number here. Meter your own tank before and after a real cycle once, and you'll have a rig-specific figure worth more than anything a spec sheet could tell you.