NOVELTY - The method comprises providing biomass comprising 65-70 wt.%, carrying out, at low temperature, harvesting the biomass at the end of fermentation, washing and concentrating the biomass and optionally lysing the biomass, and carrying out, without low temperature stress, optionally, concentrating the biomass slurry, applying heat treatment, drying the biomass to obtain the product and adjusting the pH to 7 before or after the heat treatment. The heat treatment is a high temperature/short time heat treatment carried out for 30 seconds to 5 minutes at less than 100 degrees C.    USE - The method is useful for optimizing the downstream processing of a protein-rich microalgae biomass of Chlorella (preferably Chlorella vulgaris, Chlorella sorokiniana and Chlorella protothecoides) prepared by fermentation in heterotrophic conditions and in the absence of light (all claimed), preferably optimizing production efficiency, organoleptic quality and stability over time of a protein-rich microalgae biomass.    ADVANTAGE - The optimized process is capable of producing protein-rich microalgal biomass with high yield and stability and without undesirable odors.    DETAILED DESCRIPTION - The method comprises providing biomass comprising 65-70 wt.%, carrying out, at low temperature, harvesting the biomass at the end of fermentation, washing and concentrating the biomass and optionally lysing the biomass, and carrying out, without low temperature stress, optionally, concentrating the biomass slurry, applying heat treatment, drying the biomass to obtain the product and adjusting the pH to 7 before or after the heat treatment. The heat treatment is a high temperature/short time heat treatment carried out for 30 seconds to 5 minutes at less than 100 degrees C, and is ultra high temperature carried out at a temperature of 100-150 degrees C for 5-30 seconds. The step of washing the biomass is carried out with up to 6 volumes, preferably up to 3 volumes of water for 1 volume of biomass. The method comprises neutralizing the suspension of biomass at a pH of 7 by adding potassium hydroxide and sodium hydroxide. The step of lysing the cells of the biomass is carried out by crushing, preferably ball milling. The step of concentrating the biomass is carried out by centrifuging or evaporating. The effects of the treatment steps of the microalgal biomass on the quality of the product are also determined by parameters comprising measuring the dry weight of cells in the biomass, measuring the sugar content, determining the amount of protein, analyzing of volatile organic compounds, measuring enzymatic activity, preferably lipoxygenase activity, measuring of color or content of pigment, measuring metal content, preferably iron, copper or nickel, and determining oxidation degree.