Biochemical processes involve biological catalysts at near ambient temperature and pressure in aqueous media. Understanding the physical and chemical properties of process streams requires specific analytic techniques. The relatively low concentration of analytes and products in water is a challenge for developing analytical methods. In situ methods are basically restricted to temperature and pH measurements. Ultrasensitive ex situ methods are available for liquid analysis, and optimization of biological catalysts (enzymes and fermentation organisms) is facilitated by DNA sequencing.Biochemical catalysts are often engineered to rework reactants like lignocellulosic sugars or syngas into products with high conversion efficiency and minimal byproduct formation. However, biochemical processes tend to be very sensitive to impurities, and titers are often limited because the products are often toxic to the biological catalysts if the concentration is just too high. Biochemical studies of the consequences of toxicants on organelles, cell extracts, or purified molecules, although often not considered to be in vitro systems, are actually the last word in vitro technology.