Thermal Kinetics & Altitude Compensation.

Core Relations

At 121.1°C (sea-level reference), L = 1.0. Every degree below that reference reduces the lethality rate by a factor of 10^(1/10) ≈ 1.26 per degree. Every minute of hold accumulates L minutes of equivalent F₀.

Altitude Context — Longmont, CO (4,984 ft)

At 4,984 ft, atmospheric pressure is approximately 84.4 kPa (~12.2 PSI) versus 101.3 kPa at sea level. A standard 15 PSI gauge autoclave cycle reaches an absolute pressure of ~204 kPa — producing a saturation temperature of approximately 121°C rather than the sea-level equivalent of ~127°C. The net effect: plateau temperature is similar to a lower-PSI sea-level cycle, not a true 121.1°C reference.

Our logged chamber plateau sits consistently at 118–119°C. At 118.3°C, L ≈ 0.53 — meaning each minute of hold accumulates roughly half a reference F₀ unit. Hold times are not comparable to sea-level documentation from equipment vendors or online guides. Timer parity with sea-level workflows is explicitly rejected.

Each product class has a different F₀ target derived from its contamination risk profile, density, and thermal lag characteristics. They are not interchangeable.

LC Broth & Agar — F₀ Target ≥ 20

Liquid culture broth and agar are low-density, aqueous-phase media. Heat penetrates quickly and uniformly — there is minimal thermal lag between chamber and core. The F₀ ≥ 20 target reflects the lower bioburden risk profile of these formulations relative to solid grain or substrate.

At altitude, accumulating F₀ = 20 from plateau hold alone (L ≈ 0.53/min) requires approximately 38 minutes of continuous plateau time. Ramp-phase contribution shortens this. Published hold windows account for both. The logged certificate F₀ is the authoritative verification; hold times listed on the Manifest Card are derived from actual thermal integration, not a schedule.

Grain (3 lb Red Winter Wheat) — F₀ Target ≥ 60

Dense particulate grain presents moderate thermal lag. Kernel geometry and packing density slow heat penetration to core material. The F₀ ≥ 60 target provides a significant safety margin over the theoretical minimum for endospore destruction, accounting for worst-case lag profiles and the elevated contamination risk inherent in high-starch grain substrates.

Altitude compensation at 4,984 ft: achieving F₀ = 60 from plateau alone requires approximately 113 minutes of continuous chamber hold at 118.3°C (60 / 0.53). With typical ramp contribution, actual total cycle time is substantially longer. The Kineticist calculator models this with lag-compensation. Grain is never cycled to a schedule — only to verified F₀.

Substrate (5 lb Masters Mix) — F₀ Target ≥ 120

Masters Mix substrate at 5 lb is the highest-density, highest-thermal-lag product in the lineup. The hardwood pellet and soy hull matrix retains heat poorly and conducts it slowly to the geometric center of a fully hydrated block. Core temperature lags chamber temperature by the widest margin of any product class.

The F₀ ≥ 120 target is the most conservative in the lineup by design — it is the product most vulnerable to under-sterilization and the one most commonly operated on inadequate schedules in field workflows. At altitude, achieving F₀ = 120 from plateau alone requires approximately 226 minutes of chamber hold (120 / 0.53). Ramp contribution is factored in. Extended hold windows derived from empirical run logs with temperature loggers at block core are the only accepted basis for schedule design.

Thermal Plot Publication Status