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.
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Valor z (termorresistência)
Enquanto o valor D descreve a morte microbiana numa temperatura fixa, o valor z = (T₂ − T₁)/(log D₁ − log D₂) descreve como o D muda com a temperatura. Especificamente, z é o quanto a temperatura precisa subir para o D cair a um décimo — ou seja, para a destruição ficar 10× mais rápida. Um z pequeno (ex.: 7 °C, típico de células vegetativas e leveduras) significa que a morte acelera dramaticamente com pouco aumento de temperatura — a base da pasteurização rápida (HTST). Um z grande (ex.: 10 °C, esporos bacterianos) significa que é preciso subir bastante a temperatura para acelerar a morte, exigindo a esterilização a 121 °C. O z é o que permite construir o F₀ e converter processos entre temperaturas: graficamente, é a inclinação da 'curva de morte térmica' (log D vs T). Informe duas temperaturas e seus valores D.
Related Tools
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.
Food Specific Heat (Choi-Okos)
Compute a food's specific heat by the Choi-Okos equations, cp = 4.18·Xwater + 1.55·Xprotein + 1.71·Xfat + 1.42·Xcarbohydrate + 0.91·Xash (kJ/kg·K), from the component mass fractions. Since water has a very high specific heat, wetter foods heat and cool more slowly. It is essential in computing the heat loads of cooking, refrigeration and freezing. Enter the water, protein, fat, carbohydrate and ash fractions.
Zeldovich Number
Computes the Zeldovich number of a flame, β = E_a·(T_b − T_u) ÷ (R·T_b²), the activation energy made dimensionless by the temperature rise across the flame front. It measures how sensitive the reaction rate is to a small temperature change: a high β (typically 8 to 12 for hydrocarbons) means the reaction is concentrated in a very thin layer near the flame temperature, which justifies the large-activation-energy assumption of asymptotic flame theory and the extinction and cellular-instability criteria. The universal gas constant R = 8.314 J/(mol·K) is adopted, with activation energy in J/mol and temperatures in kelvin. Enter the activation energy, the burned gas temperature and the unburned gas temperature.
Cheese Yield (Van Slyke Formula)
Estimates how many kilograms of cheese come out of 100 kg of milk using the Van Slyke formula: 93% of the milk fat is added to the casein content, 0.1 point is discounted as loss to the whey, the sum is multiplied by 1.09 to include the salt and ash retained in the curd, and all of it is divided by (1 minus the cheese moisture). The result is the theoretical yield, the reference against which the real plant loss is measured: a gap above half a point between the theoretical figure and the vat balance is almost always fat escaping into the whey or curd cut at the wrong moment. Note that moisture sits in the denominator and dominates the result — the same milk yields 11.2 kg in a soft cheese at 45% moisture and only 9.5 kg in a hard cheese at 35%, and that difference is water, not solids, so a high yield on its own does not mean a better process. The classic Van Slyke form was adopted, with the 0.93 fat retention coefficient and the 1.09 factor; dairies usually recalibrate both numbers for their own process, and for milk standardised by ultrafiltration the formula underestimates the yield. Enter the milk fat, the milk casein and the target cheese moisture.
Cold Room Heat Load
Compute the product cooling heat load in a cold room, Q = m·cp·ΔT, from the product mass, its specific heat and the desired temperature change. It is the sensible-heat portion to remove to lower the product temperature — one of the components of the room's total load (which also includes wall transmission, infiltration, lighting, motors and people). It defines the refrigerating capacity needed. Enter the mass, the specific heat and the ΔT.
Rail Thermal Force (CWR)
Calculate the axial thermal force in a continuous welded rail (CWR), F = E·A·α·ΔT, from the steel elastic modulus E (Pa), the rail section area A (m²), the thermal expansion coefficient α (1/°C) and the temperature change ΔT from the neutral temperature (°C). In CWR — where rails are welded into hundreds-of-metre or kilometre strings, removing joints — thermal expansion is PREVENTED by track fastening, so a temperature change, instead of changing length, generates a huge internal axial force: compression in heat (risk of track buckling, which misaligns the rails) and tension in cold (risk of rail or weld fracture). Since the force does not depend on length (only section and ΔT), it can reach hundreds of kN. So CWR is installed at a neutral (stress-free) temperature chosen mid-range, minimizing compression and tension extremes. This is essential to modern track safety and to set the laying neutral temperature. Enter the elastic modulus, section area, expansion coefficient and temperature change.
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