🍎 Falling number (α-amylase activity) in wheat, rye and flours — the Hagberg-Perten method
In short
A suspension of 7 g of flour (at a moisture content of 15 %) in 25 ml of water is gelatinised in a viscometer tube in a boiling bath, stirred for 60 s with a stirrer (2 strokes/s); the total time from the immersion to the fall of the stirrer in the gel liquefied by the α-amylase is the falling number in seconds. The test is performed according to PN-EN ISO 3093:2010; Test portion: 7 g of flour or meal at a moisture content of 15 %; a table of corrections 6.10–8.00 g for moisture contents of 5–23.8 %. The procedure comprises 8 steps (about 1 min in total); it is used for: Assessment of the baking value of wheat and rye flour and of the suitability of grain for consumption purposes, Detection of sprouted grain at collection (deductions or rejection of a batch of milling wheat), The choice of blends of flours of various α-amylase activity and of „improvers" in baking.
At a glance
- Standard: PN-EN ISO 3093:2010
- Category: Food chemistry
- Procedure steps: 8
- Total time of stages: 1 min
- Test portion: 7 g of flour or meal at a moisture content of 15 %; a table of corrections 6.10–8.00 g for moisture contents of 5–23.8 %
- Water: 25 ml distilled, 20 ± 5 °C, added with a pipette
- Stirring: Start 5 s after the immersion, 60 s, 2 strokes/s; the stirrer 25 ± 0.05 g
Overview
The standard specifies the determination of the α-amylase activity of cereals by the falling number (FN) method according to Hagberg-Perten; it concerns cereal grain, in particular wheat and rye and the flours from them, durum wheat and semolina, and it is not suitable for determining low levels of α-amylase activity. The falling number is the total time in seconds, counted from the immersion of the viscometer tube in boiling water, needed to set the viscometer stirrer in motion in a defined way and for it to fall a defined distance in a gel of flour or meal and water which is being liquefied as a result of the action of the α-amylase. By converting into the liquefaction number (LN) one can estimate the composition of blends of grain or flours of known falling numbers. The fourth edition ISO 3093:2009 is a minor revision of the edition of 2004; the standard draws attention to a patent concerning the falling number apparatus (Perten Instruments AB). The description is based on the preview of the standard (the scope and the definitions) and on the instructions for the Polish automatic apparatus conforming to PN/ISO 3093.
The falling number is a measure of the activity of α-amylase, which in grain properly ripened and harvested in dry conditions occurs in small amounts; at a moisture content of the cereal above 15 % in unfavourable weather conditions (sprouting, germination in the ear) the enzyme becomes active and damages the starch, and doughs from such flours have unfavourable properties and do not guarantee good bread. The lower the falling number, the higher the activity of the amylases: for wheat flour below 80 s (for rye flour below 70 s) means a very high activity and unsuitability for direct baking, 170–200 s (125–200 s) — a medium activity, suitable for baking, and above 300 s (250 s) — a low activity. Drying the grain after the harvest stabilises its condition, but does not repair the enzymatic damage that arose in the field.
In the breeding of varieties resistant to sprouting, use is made of the difference of the falling number between a control sample and a sample after induced sprouting, and of Weilenmann’s falling number index; in the studies of IHAR the falling number of the control kernels of 20 varieties of winter wheat fell within the range 233–432 s, and the induction of sprouting lowered it by 82–100 s.
Method principle
The grain is milled into flour in a laboratory mill (a milling conforming to the requirements of the standard affects the result) and a test portion is weighed out corresponding to 7 g of a product with a moisture content of 15 % — the mass is corrected according to a table from 6.10 g (a moisture content of 5 %) to 8.00 g (a moisture content of 23.8 %). The test portion is transferred into a viscometer tube (internal diameter 21 ± 0.02 mm, external 23.8 ± 0.25 mm, internal height 220 ± 0.3 mm), 25 ml of distilled water at a temperature of 20 ± 5 °C are added with a pipette, it is closed with a stopper and shaken (10 s in a shaker or 20 times by hand), after which the stirrer is put in (a mass without the stopper of 25 ± 0.05 g, stainless steel), scraping the suspension off the walls with it. The tube is immersed in the boiling water of the bath; after 5 s the drive begins to stir at a rate of two strokes per second (one movement up and one down), and after 60 s the stirrer is released in the upper position and falls through the gel. The total time of the stirring and of the fall is the falling number in seconds. The result is the arithmetic mean of two determinations, whose difference must not exceed 10 % of their mean.
Applications
- Assessment of the baking value of wheat and rye flour and of the suitability of grain for consumption purposes
- Detection of sprouted grain at collection (deductions or rejection of a batch of milling wheat)
- The choice of blends of flours of various α-amylase activity and of „improvers" in baking
- Selection of cereal varieties resistant to sprouting (the difference of the falling number, Weilenmann’s index)
- A quality requirement in specifications for cereal grain and flour
Key parameters
| Parameter | Value |
|---|---|
| Test portion | 7 g of flour or meal at a moisture content of 15 %; a table of corrections 6.10–8.00 g for moisture contents of 5–23.8 % |
| Water | 25 ml distilled, 20 ± 5 °C, added with a pipette |
| Stirring | Start 5 s after the immersion, 60 s, 2 strokes/s; the stirrer 25 ± 0.05 g |
| Viscometer tube | Internal diameter 21 ± 0.02 mm, external 23.8 ± 0.25 mm, internal height 220 ± 0.3 mm |
| Result | Seconds; the mean of two determinations, the difference ≤ 10 % of the mean |
| Interpretation (wheat flour) | < 80 s a very high α-amylase activity; 170–200 s suitable for baking; > 300 s a low activity |
Standard
- Standard number
- PN-EN ISO 3093:2010
- Title (PL)
- Pszenica, żyto i mąki z nich uzyskane, pszenica durum i semolina — Oznaczanie liczby opadania metodą Hagberga-Pertena
- Title (EN)
- Wheat, rye and their flours, durum wheat and durum wheat semolina — Determination of the falling number according to Hagberg-Perten
Step-by-step procedure
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Preparation of the apparatus
Set the apparatus on a stable table in a room at a temperature of about 22 °C, fill the reserve tank with distilled water, bring the bath to the boil (the ready message).
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Milling
Mill the grain tested into flour in a laboratory mill in accordance with the requirements of the standard; test flour and semolina directly.
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Test portion
Weigh out 7 g of flour (the test portion for a moisture content of 15 %); at a different moisture content weigh out the mass from the table of corrections (for example 6.60 g at 11 %, 7.45 g at 19 %).
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Suspension
Transfer the test portion into the viscometer tube, add with a pipette 25 ml of distilled water at 20 ± 5 °C, close it immediately with the stopper and shake for 10 s in a shaker or 20 times by hand with an up-and-down movement until the suspension is homogeneous; take the stopper out.
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Stirrer
Put the stirrer into the tube, scraping into the suspension with it the flour adhering to the walls.
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Measurement
Place the tube with the stirrer in the holder and immerse it in the boiling bath, lock it with the catch and start the drive. After 5 s the drive stirs the suspension for 60 s at a rate of 2 strokes/s, after which it releases the stirrer in the upper position; the apparatus counts the time until the stirrer falls and displays the falling number in seconds.
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Repetition and result
Carry out a second determination; the difference must not exceed 10 % of the mean. Give as the result the arithmetic mean of both determinations in seconds. The regularity of the stirring is the most important condition of a correct determination — its absence leads to considerable differences.
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Cleaning
Take the tube out, clean it and the stirrer of the gel under running water or in a laboratory washer and wipe them dry.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Falling number apparatus | A water bath of 1600 ml maintaining boiling, a reserve tank of 5 l with a pump, a stirrer drive with a 60 s countdown, a display of the falling number; the type SWD-automat (ZBPP Bydgoszcz) conforming to PN/ISO 3093 | — |
| Viscometer tubes with stoppers | Glass, 21 ± 0.02 mm × 220 ± 0.3 mm internally | — |
| Viscometer stirrer | Stainless steel, calibrated, a mass without the stopper of 25 ± 0.05 g | — |
| Laboratory mill | For example WŻ-2 (ZBPP) or Mill 3100 — the milling conforming to the standard | — |
| Laboratory balance, 25 ml pipette, shaker | A mechanical shaker or mixing by hand (20 movements); a 500 µm sieve | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Distilled water | — | 25 ml per determination, 20 ± 5 °C; also for filling the bath (avoiding scaling) |
Health and safety (OHS)
- The boiling water bath — introduce the tube in the protective holder, the perspex screen closed; a risk of scalding by steam
- A 1000 W heating device supplied from the mains with an earth — do not leave it unattended, do not touch the plug with wet hands
- Flour dust from the milling — ventilation, if necessary a dust mask
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 3093:2010 — “Wheat, rye and their flours, durum wheat and durum wheat semolina — Determination of the falling number according to Hagberg-Perten”.
How does this method work?
The grain is milled into flour in a laboratory mill (a milling conforming to the requirements of the standard affects the result) and a test portion is weighed out corresponding to 7 g of a product with a moisture content of 15 % — the mass is corrected according to a table from 6.10 g (a moisture content of 5 %) to 8.
What is the measuring range and accuracy?
Test portion: 7 g of flour or meal at a moisture content of 15 %; a table of corrections 6.10–8.00 g for moisture contents of 5–23.8 %; Water: 25 ml distilled, 20 ± 5 °C, added with a pipette; Stirring: Start 5 s after the immersion, 60 s, 2 strokes/s; the stirrer 25 ± 0.05 g; Viscometer tube: Internal diameter 21 ± 0.02 mm, external 23.8 ± 0.25 mm, internal height 220 ± 0.3 mm.
How long does the test take?
The times given for the individual stages add up to approximately 1 min. The procedure comprises 8 steps.
What equipment is required?
Falling number apparatus, Viscometer tubes with stoppers, Viscometer stirrer, Laboratory mill, Laboratory balance, 25 ml pipette, shaker.
Where is this test used?
Assessment of the baking value of wheat and rye flour and of the suitability of grain for consumption purposes; Detection of sprouted grain at collection (deductions or rejection of a batch of milling wheat); The choice of blends of flours of various α-amylase activity and of „improvers" in baking; Selection of cereal varieties resistant to sprouting (the difference of the falling number, Weilenmann’s index); A quality requirement in specifications for cereal grain and flour.
What safety precautions apply?
The boiling water bath — introduce the tube in the protective holder, the perspex screen closed; a risk of scalding by steam; A 1000 W heating device supplied from the mains with an earth — do not leave it unattended, do not touch the plug with wet hands; Flour dust from the milling — ventilation, if necessary a dust mask.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 3093.