Risograph

What is a Risograph?

The risograph is a yeast activity testing instrument that studies dough development and gas release during a proofing process. It measures the production of gas by yeast during fermentation and the maximum height reached by dough while recording the total gas released during proofing.

The risograph helps bakers to:

• Adjust yeast levels in dough for optimum volume according to type of baked good
• Classify yeast forms according to end application
• Predict yeast performance during fermentation and proofing
• Adjust proofing and fermentation conditions (e.g. temperature, humidity)

Origin

The risograph testing instrument was developed and commercialized by National Manufacturing Co., a division of TMCO (Total Manufacturing Company) located in Lincoln, Nebraska which specialized in supplying laboratory equipment to universities and federal cereal chemistry research organizations.

How does it work?

The risograph method determines the total gas production of yeast, expressed in volume (mL), at standard barometric (atmospheric) pressure over time. This instrument uses sealed chambers containing dough or yeast slurry samples to measure outgassing. The outgassing is beneficial in determining yeast activity and dough properties.  The risograph comes with a computer software that charts all relevant data from the test.

The risograph permits comparison of gassing activity among various samples of yeast and provides a means to monitor yeast fermentation performance. The risograph can be used to evaluate any commercial yeast form, including:

• Compressed yeast (CY) with approximately 30% solids
• Active dry yeast (ADY) with approximately 92% solids
• Instant dry yeast (IDY) with approximately 95% solids

Formulas containing 0, 8, and 20% sugar (based on flour weight) can be used for different tests. Dough formulations must be calculated so that equal weights of dough contain equal weights of yeast solids (0.70 g of yeast solids per 100 g of dough).

Application

The AACC Method 89-01 describes a procedure for using the risograph. This method allows the  use of any suitable instrument for measuring gas pressure or volume evolved during dough fermentation. The test consists of the following steps for compressed and active dry yeasts:¹

• Pretreatment of yeast
  • For CY: 5 min before mixing, weigh 0.01 g of compressed yeast and crumble it into a beaker and soak in distilled water at 70°F (21°C) to allow  the yeast to rehydrate. See formulas in Table I.
  • For ADY: in a warm to room temperature environment and for at least 30 min before use, prepare a 3% sugar solution with water for yeast rehydration (see formulas) in a beaker (rehydration water is 4–5 times weight of yeast). Then, weigh 0.01 g of dry yeast and add to sugar solution with initial mild hand stirring. Rehydrate at 110°F (43°C) for 10 min with sufficient stirring to obtain uniform suspension of yeast.
• Mixing of dough
  • Weigh all dry ingredients except yeast and place into mixer bowl. Temperature circulator should be set to desired temperature, about 86°F to bring dough to a temperature of 86 ± 2°F (30 ± 1°C).
  • Add yeast suspension to mixer bowl. Use the rest of water for dough hydration to rinse in yeast (see formulations). Mix dough to full development and to 86 ± 2°F (30 ± 1°C).
  • Give dough 5-min bench rest while measuring temperature.
• Determination of gas production
  • Place dough piece (of proper size) into each chamber of gas-measuring device. Permit 5-min period for temperature equilibration. Then start gas measurement at 86 ± 2°F (30 ± 1°C). Measure gas evolution over 90-min period.
  • Report total volume of gas (evolved after 90 min) per hour. If pressuremeter is used, values must be converted to volume of gas at standard barometric pressure.

Table I. Dough formulas for compressed and active dry yeast

Relevant considerations

• Yeast activity in terms of gas production is greatly affected by processing conditions (e.g. temperature) and formulation (water, salt, sugars, nutrients, acidity).
• All formulations are based on 100 g of flour and may be scaled up or down. The water absorption levels can also be modified according to user needs. Formulas must always use  0.70 g of yeast solids per 100 g of dough.
• Adjust dough weight to permit easy handling for internal volume of gas measuring device.
• The risograph is not intended to predict performance of a given yeast in the bakery as variations in formulation and processing conditions may be different in high-speed production.

References

1. AACC International. Approved Methods of Analysis, 11th Ed. Method 89–01. Yeast Activity, Gas Production. Final approval October 26, 1994; Reapproval November 3, 1999. Cereals & Grains Association, St. Paul, MN, U.S.A.