Hen egg white lysozyme is a hydrolytic enzyme effective at preventing the growth of Gram positive bacteria by degrading the bacterial cell wall to a point of cell lysis. Investigating lysozyme as a processing tool in wine to control the growth of lactic acid bacteria and malolactic fermentation has significant commercial interest. In this project, the interactions of lysozyme with wine components and wine was evaluated along with the efficacy of lysozyme in preventing malolactic fermentation (MLF) in Oregon Pinot Noir and Chardonnay. The information from this work, together with results from similar projects, will allow the development of guidelines for lysozyme use in commercial wine. Interactions of lysozyme with wine components were evaluated by measurement of enzymatic activity in the presence of wine acids, ethanol, and phenolics. Enzyme inhibition was observed, to various degrees, with all wine components. Crude grape tannin altered the availability of free enzyme by complexing to lysozyme and forming a precipitate. In a model wine system, lysozyme activity was reduced by 50% when tannin was present. Lysozyme addition to red wine resulted in a reduction in pigmented compounds and detectable sensory differences. Wine trials evaluated the efficacy of lysozyme in completely preventing malolactic fermentation (MLF) and terminating MLF midway through fermentation in Oregon Pinot Noir and Chardonnay. Vintages from 1993 and 1994 were treated without SO₂, with SO₂, with SO₂ plus a starter culture of Leuconostoc oenos. Each lot was divided into 0 ppm lysozyme (control), 250 ppm lysozyme, 500 ppm lysozyme, and 1000 ppm lysozyme. Lactic acid bacteria were enumerated monthly, for ten months. Lysozyme prevented malolactic fermentation in all wines at the treatment levels of 500 and 1000 ppm. In the 1993 Pinot Noir, 250 ppm lysozyme prevented MLF but only delayed MLF in the 1994 vintage. Lysozyme effectively terminated MLF at a concentration between 200 and 300 ppm in both Pinot Noir and Chardonnay. / Graduation date: 1996