Written by Mirco Rossetti, Application Specialist | July 17, 2023
Microwave ashing procedure for determination of inorganic
ash in food samples
The ashing test on food samples is
commonly used for evaluation of mineral
The minerals constituents include
potassium, sodium, calcium and
magnesium, which are present in larger
amounts as well as smaller quantities of
aluminum, iron, copper, manganese or
zinc, arsenic, iodine, fluorine and other
elements present in traces.
Determination of ash content is very
important for several reasons. Mineral
content in food play an important role from
a physicochemical and nutritional point of
Ash content analysis is also an accepted
index of refinement of foods, such as
wheat flour or sugar production, since the
ash test is a reliable indicator of efficiency
of which the separation of bran and germ
from the rest of the wheat kernel.
Traditional tools like electrical muffle
furnaces, have their own set of limitations –
long ashing time, long cooling, high power
consumption and low aspiration efficiency.
Milestone PYRO system incorporates all of
the benefits of a microwave system
working with special fast heating/cooling
crucibles while making the ashing
application fast, easy, effective, and in
The new Milestone PYRO is an advanced
microwave muffle furnace, suitable for food
It is equipped with a full stainless-steel
door and the cavity has a volume in excess
of 70 liters, thus allowing the use of a large
muffle which in turn enhances the sample
PYRO system is equipped with two 950
Watt magnetrons for a total of 1900 Watt
making it the most powerful microwave
muffle furnace system available in the
The system additionally employs a rotating
diffuser that evenly distributes the
microwaves throughout the cavity,
assuring a uniform temperature improving
PYRO enables the analysts to perform the
ashing test of a wide variety of samples.
A unique ceramic muffle allows microwave
radiation to pass through and rapidly raise
the temperature of a silicon carbide plate.
Sample crucibles are placed on a large
clean quartz plate and an airflow is induced
by a built-in exhaust system.
Any type of crucible (metal, porcelain,
quartz, etc.) can be used and for this test
we have used the Milestone UltraFAST
crucibles (Picture on the right).
The UltraFAST crucibles are made of an
innovative material that, although
chemically and thermally resistant, allows
the samples to be surrounded by a
constant airflow which accelerates the
ashing process. Furthermore, just 30
seconds are enough for the UltraFAST
crucibles to go from 1000°C to room
We have weighed accurately 4 g of Wheat
flour and 1 g of BCR-380R (Milk powder) in
UltraFAST crucibles (see details in Table 1).
The crucibles were initially preconditioned
at constant weight (preconditioning step
time is reduced thanks to the short cooling
time of UltraFAST crucibles).
Crucibles were here placed into PYRO
microwave ashing unit and ashed with the
RESULTS AND DISCUSSION
The samples were completely ashed,
obtaining a white residue of inorganic
material. The crucibles were weighted and
percentage of residue was then
recalculated. Results are reported in the tables on the left.
Milestone’s PYRO microwave ashing offers
the big advantage to run all samples in only
one step ensuring full of operations and
Due to its higher muffle capacity, faster
heating and UltraFAST crucibles, the
sample processing throughput is higher
than conventional electrical muffle system.
The results shown in this report are very
reproducible thanks to the great
temperature homogeneity across all the
muffle while the recoveries on certified
standard material are in compliance with
the certificate value.
This application report demonstrate how PYRO is a great tool to perform
ashing of food samples.
The use of microwave heating for dry ashing applications has been represented a breakthrough in the process and quality control of samples like polymers, petroleum, food and feeds, pulp paper and pharmaceuticals.