In some markets, the different available flour varieties are labeled according to the ash mass that remains after a sample is incinerated in a laboratory oven (typically at or , see international standards ISO 2171 and ICC 104/1). This is an easily verified indicator for the fraction of the whole grain remains in the flour, because the mineral content of the starchy endosperm is much lower than that of the outer parts of the grain. Flour made from all parts of the grain (extraction rate: 100%) leaves about ash or more per dry flour. Plain white flour with an extraction rate of 50–60% leaves about .