Technologies K–10 · Years 5–6

Why bread dough rises: yeast and temperature

Living World (NSW Science and Technology K–6, 2017, food production); Design and Technologies: Knowledge and understanding, Technologies context: Food specialisations (ACARA v9)

PracticalMedium risk

School laboratory, not for home

In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

The idea

Yeast ferments sugar in dough and gives off carbon dioxide that makes the dough rise, and it works faster in warm conditions, which is why bakers prove dough somewhere warm.

Safety card

Medium riskA teacher supervises

Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

Hazards

Scalds from hot water used to warm the baths
Wheat and yeast allergy
Slippery flour on the floor

Controls

An adult tops up the water baths; baths no hotter than 40 °C
Check allergy plans; nothing is eaten
Sweep spills at once

Note

Heat is involved: record the activity on Primary School RiskAssess (riskassess.com.au).

What you need

25 g plain flour and 1 g sugar per group
30 mL of yeast suspension per group (7 g of dried yeast stirred into 450 mL of warm water, made by the teacher)
1 × 250 mL measuring cylinder and 1 × 50 mL measuring cylinder per group
Water baths at 20 °C, 30 °C and 37 °C (large containers topped up with warm water by an adult) and a thermometer
Beaker, spoon, a wide funnel; timer; graph paper

How to do it

Mix the flour and sugar in the beaker, add the 30 mL of yeast suspension and stir to a smooth, pourable paste.
Pour the paste into the 250 mL cylinder through the funnel without touching the sides, and note the volume.
Stand the cylinder in your group's water bath and record the temperature.
Record the volume every 2 minutes for 30 minutes.
Plot volume against time and put every group's line on one class graph.
Explain which temperature a baker should use to prove dough, using the graph.

What you should see

The dough rises fastest at 37 °C, more slowly at 30 °C and slowest at 20 °C, so the 37 °C line is steepest. The Royal Society of Chemistry notes that after 35 to 45 minutes the gluten network breaks and gas escapes, so the volume stops rising. The learner knows it worked when all three lines rise and their order by steepness matches the temperatures.

What changes

What you change: water bath temperature (20, 30, 37 °C)
What you measure: dough volume every 2 minutes
What you keep the same: 25 g flour, 1 g sugar
30 mL of the same yeast suspension
the same size cylinder
the same time of mixing

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Yeast is a chemical powder (it is a living microorganism).
Hotter is always faster (very hot water kills yeast).
Dough rises because it absorbs air (the gas is carbon dioxide made by the yeast).

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science and Technology K–6 Syllabus (2017), NESA. The syllabus taught in 2026; the 2024 syllabus replaces it from 2027. Code read from the official syllabus document (DOCX) on 2026-09-22.ST3-5LW-T ST3-2DP-T
Science and Technology K–6 Syllabus (2024), NESA. Implementation from 2027, so this code describes the future syllabus. Code read from the Stage 3 content page on 2026-09-22. Skill outcome only: neither Stage 3 focus area has a food or fibre content point; the entry is a fair test with the variables it lists.ST3-PQU-01
Australian Curriculum v9AC9TDE6K04

Sources

The pages the author read to write this activity.

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