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IB Biology IA idea · Microbes and antibiotics (school-safe only)

IB Biology IA idea: how much salt is too much for rising dough?

Salt flavours bread and also slows the yeast. Find out how much it takes to stall the rise.

  • Microbes and antibiotics (school-safe only)
  • SL ideal
  • HL good
  • Lab

By Photon Academy · Updated 13 November 2026

These ideas are starting points, not an IA to copy. Never copy an idea blindly: make the question, method and analysis your own, and check your plan with your teacher.

Example research question

To adapt, never to copy

How does salt concentration in the dough water (0, 0.5, 1, 2, 3 and 4 %) affect the rate of dough volume increase (cm³ h⁻¹) in measuring cylinders over 3 hours at 28 °C?

Change the system, the range or the method so the question is yours. Check it against the research question checklist in our Biology IA guide.

Variables

You change
salt concentration in the dough water, 0 to 4 percent, 6 or more values
You measure
dough volume increase in a clear cylinder, cm3 per hour
You keep the same
  • same flour, yeast and water amounts
  • same starting temperature and kneading
  • same container shape
  • same room temperature

Method

Mix small equal batches of dough with different salt amounts, press them into measuring cylinders and mark the height at set times over 2 to 3 hours. Photograph the cylinders with a ruler beside.

Data analysis

Rise rate against salt percent, mean and standard deviation (n of 3), curve fit; link to osmotic stress on yeast. Measurement uncertainty from reading the top of a soft dough.

How it works

You change Salt concentration (%) and measure Dough rise rate (cm³ h⁻¹) in Small flour and yeast doughs, keeping Dough mass, Flour type, Temperature, Starter amount the same. Expect a graph of Rate of dough rise / cm³ h⁻¹ against Salt concentration / %: Strong salt stresses the yeast, so the rise should slow.

Make it yours

Use sugar in place of salt, or compare fast-acting yeast with a sourdough starter.

Safety

Do not eat dough made in the lab. Keep surfaces clean.

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