SOP: Total Ash in Spices and Condiments

GIFSQ — Global Institute for Food Safety & Quality

Principle

The sample is carbonized and ignited in a muffle furnace until all carbon is removed; the mineral residue remaining after ignition is the total ash. Spices whose ash resists burning white are leached with hot water to remove soluble salts before re-ignition; mustard flour, which chars stubbornly, is treated with nitric acid between ignitions.

Apparatus required

• Flat dish
• Muffle furnace
• Bunsen burner (for charring)
• Quantitative filter paper
• Steam bath
• Desiccator

Procedure

Spices and condiments except ground mustard or mustard flour:

Weigh 2 g of the sample into a flat dish

↓

Place the dish at the entrance of the muffle furnace until the sample is well carbonized — do not allow the sample to catch fire; alternatively, char over a bunsen burner, taking care not to ignite the sample

↓

For most spices, ash at 550 to 600 °C for 2 hr — for nutmeg, mace, ginger and cloves, ash at 600 ± 20 °C

↓

If carbon remains, leach the ash with hot water, filter through a quantitative filter paper, wash the paper thoroughly and transfer the filter paper along with the residual ash to the original dish

↓

Dry and ignite in the muffle furnace at 600 °C until the ash is white, cool the dish, add the filtrate, evaporate to dryness on a steam bath, and heat in the muffle for 30 min

↓

Cool and weigh

Ground mustard or mustard flour:

Ash the sample at 600 °C for 2 hr, leach the ash with hot water, filter, and wash thoroughly with hot distilled water

↓

Transfer the filter paper and contents to the original dish, dry and heat in the muffle furnace for 30 min

↓

Remove the dish, allow to cool, add 5–10 drops of HNO₃, evaporate to dryness, and heat in the furnace for 30 min

↓

Repeat the treatment with HNO₃ and heating, if necessary, until the ash is white

↓

Cool in a desiccator and weigh

Calculation

Ash % = (Wt of ash × 100) / Wt of sample (g)

Where,

• Wt of ash = weight of the residue remaining after ignition
• Wt of sample (g) = weight of the sample taken

Precautions

• Do not allow the sample to catch fire during charring.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.