A method of preparing a coagulated plant protein fraction with a medium molecular weight of between 14 to 97, by providing fruit juice in aqueous solution; precipitating a high-molecular-weight plant protein fraction whose bulk has a molecular weight of from above 100 to 600, by adjusting an acidic pH and/or a temperature above room temperature, and mechanically separating the fraction precipitated thus; precipitating a medium-molecular-weight coagulated plant protein fraction under warm conditions by treating, at pH 2 to 7, and between 60 to 90.degree. C., the solution obtained after separation of the high-molecular-weight plant protein fraction and mechanically separating the medium-molecular-weight coagulated plant protein fraction with a molecular weight of between approximately 14 to 97, with the bulk of the molecular weight distribution being between 20 to 60. The plant protein fraction is usable as foodstuff, food additive, additive in pharmaceuticals, animal feed, in cosmetics, as industrial protein, as adhesive.