Decimal Reduction Time (D-Value)
Compute the decimal reduction time (D-value) of a microorganism, D = t/(log N₀ − log N), the time needed, at a given temperature, to destroy 90% of the population (a one-log reduction). It is the fundamental parameter of thermal death kinetics in food processing: the larger the D, the more heat-resistant the microorganism. Enter the heating time and the initial and final populations.
Result
—
Tempo de redução decimal (valor D)
A morte de microrganismos por calor segue uma cinética logarítmica: numa temperatura constante, cada intervalo de tempo igual destrói a mesma fração da população, não o mesmo número. O valor D = t/(log N₀ − log N) é o tempo para reduzir a população a um décimo (90% de morte, um 'ciclo log'). Se D = 2 minutos, então em 2 min sobra 10%, em 4 min sobra 1%, em 6 min sobra 0,1%, e assim por diante — a esterilização nunca chega matematicamente a zero, apenas a probabilidades cada vez menores (daí o conceito de '12D' para o botulínico: 12 reduções decimais, garantindo segurança esmagadora). O D depende fortemente da temperatura (mais quente, D menor) e do microrganismo (esporos são muito mais resistentes que células vegetativas). É o tijolo da engenharia de processos térmicos de alimentos. Informe o tempo e as populações inicial e final.
Related Tools
z-Value (Thermal Resistance)
Compute a microorganism's z-value, z = (T₂ − T₁)/(log D₁ − log D₂), the temperature change needed to alter the D-value (decimal reduction time) by a factor of 10. The z measures the microorganism's temperature sensitivity: the smaller the z, the more the destruction accelerates with heating. It is the basis of converting between processes at different temperatures (F₀, pasteurization). Enter two temperatures and their corresponding D-values.
Microbial Lethality
Compute the lethality rate (L-value) of a thermal process, L = 10^((T − Tref)/z), the factor indicating how many times faster (or slower) microbial destruction at a temperature T is than at the reference temperature. Integrated over time, the lethality gives the process F-value. It is the basis of the general-method sterilization calculation, which sums the lethality over the product's actual thermal history. Enter the temperature, the reference temperature and the z-value.
Food Water Activity
Compute a food's water activity (aw) from the equilibrium relative humidity, aw = ERH/100. Water activity — the 'free water' available for reactions and microorganisms — is the most important conservation factor: below aw 0.6 no microorganism grows; bacteria stop at ~0.90, molds at ~0.70. Unlike total moisture, it explains why honey (moist but with low aw) does not spoil. Enter the equilibrium relative humidity (%).
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.