Second and third grade fish sauces are made by adding salt water to cover the fish remains, letting sit for 2-3 months each time, then filtering before bottling. Finally, the fish remains are boiled with salt water, then strained out and discarded, to produce the lowest grade fish sauce; or they may be added to other fish remains from the first fermentation in the process of making second-grade sauce. Because flavor is substantially reduced with each fermentation, top-grade fish sauce is frequently added to the lower grades to improve their flavor. In fact, many manufacturers do not market top-grade, 100-percent fish sauce, saving it instead to mix with second and third grade sauces in order to produce larger quantities to sell that can still qualify as genuine fish sauce..