pH, a scale of measurement of the concentration of the effective, active acidity in a solution and an important statistic, of relevance to how vines grow, how grapes ripen, and how wine tastes, looks, and lasts. (The technical definition is that pH is the negative logarithm of the all-important hydrogen ion activity or concentration.) Low values of pH indicate high concentrations of acidity and the tart or sour taste that occurs in lemon juice, for example. Values near 7 are effectively neutral; drinking waters have pH values near 7. Values between 7 and 14 are found in basic or alkaline solutions such as caustic or washing soda. Grape must and wine are acidic, with pHs generally between 3 and 4. The scale is logarithmic so a solution with a pH value of 3 has ten times as much hydrogen ion activity as one whose pH value is 4.