Moisture: Dry / Wet Basis
Convert a food's moisture from wet basis to dry basis, Xdb = Xwb/(1 − Xwb), where Xwb is the water fraction relative to total mass (wet basis) and Xdb relative to dry mass. The dry basis is preferred in drying calculations because the denominator (dry mass) does not change during the process, unlike the total mass. Confusing the two bases is a common and serious error. Enter the wet-basis moisture (fraction).
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Umidade: base seca / úmida
Há duas formas de expressar a umidade de um alimento, e confundi-las gera erros graves. A base úmida (Xbu) é a fração de água em relação à massa total (água + sólido seco) — é a que o consumidor entende ('a melancia tem 92% de água'). A base seca (Xbs) é a fração de água em relação à massa de sólido seco apenas: Xbs = Xbu/(1 − Xbu). Por que a base seca? Porque na secagem, a massa total diminui à medida que a água sai (a base úmida, com denominador móvel, complica as contas), mas a massa de sólido seco permanece constante — então a base seca dá uma relação linear e estável para modelar a cinética de secagem. Os engenheiros de alimentos quase sempre trabalham em base seca; rótulos e o público, em base úmida. A diferença é enorme em alimentos muito úmidos: 80% base úmida equivale a 400% base seca (4 kg de água por kg de sólido)! Informe a umidade em base úmida.
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Constant-Rate Drying Period Time
Computes how long the constant-rate period of a tray drying run lasts, t = m_s × (X₁ − X_c) ÷ (A × N_c), that is, the mass of water to be evaporated divided by the surface evaporation rate. Moisture contents are on a dry basis, in kilograms of water per kilogram of dry solid, and N_c is the evaporation flux measured while the surface is still fully wet, in kg per square metre per hour. While this period lasts the surface behaves like an open pool and the rate does not depend on the material, only on the air; it ends at the critical moisture X_c, when internal water can no longer reach the surface as fast as it evaporates. Enter the dry solid mass, the initial and critical moisture contents, the exposed area and the constant evaporation rate.
Falling-Rate Drying Period Time
Computes the duration of the falling-rate drying period under the model where the rate drops linearly with free moisture starting at the critical moisture: t = m_s × X_c ÷ (A × N_c) × ln(X_c ÷ X₂). Moisture contents go in as free moisture on a dry basis, that is, with the equilibrium moisture already subtracted, which is why X₂ can never be zero — drying down to equilibrium would take infinite time, exactly what the logarithm says. Compared with the constant-rate period this is the expensive stretch: every kilogram of water removed costs far more time than in the previous stretch, because internal transport now sets the pace. Enter the dry solid mass, the critical moisture, the final free moisture, the exposed area and the constant rate at the critical moisture.
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 (%).
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Gear Base Diameter
Calculate the base circle diameter of an involute gear, d_b = d·cos(φ), from the pitch diameter d (mm) and the pressure angle φ (degrees). The base circle is the circle from which the INVOLUTE tooth profile is generated — the standard profile of modern gears. The involute is the curve traced by the tip of a string unwinding from a cylinder: that cylinder is exactly the base circle. The entire active tooth profile (the part that actually transmits force) is ABOVE the base circle; below it there is no involute profile. The base diameter is fundamental in gear geometry because it defines the involute profile and, with it, key properties: the LINE OF ACTION (the line tangent to both base circles of the mesh, along which tooth contact travels, always in the same direction — why involute gears transmit uniform motion), the base pitch and the contact ratio. The relation d_b = d·cos(φ) shows that the pressure angle is the angle between the line of action and the tangent to the pitch circles. It is an essential parameter in designing and manufacturing (generating) involute gears. Enter the pitch diameter and the pressure angle.
Potential Alcohol from Brix
Estimate the potential alcohol of a must (wine, beer, kombucha) from the sugar content in degrees Brix, %ABV ≈ Brix · 0.55, assuming complete fermentation of the sugars. Brix measures the soluble solids (mostly sugar) of the must; fermentation converts that sugar into alcohol and carbon dioxide. It is a quick estimate used by winemakers and brewers to predict the final strength. Enter the content in degrees Brix.
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.