Lactose Intolerance


Intestinal gas—not a very pleasant thought! It can be a big problem for those individuals who lack the enzymes to digest certain foods. Do products that advertise that they eliminate these problems really work?


  • Enzyme

  • Disaccharide
  • Monosaccharide


Some individuals produce insufficient quantities of lactase, an enzyme that breaks the bonds in lactose (milk sugar). Lactose is a disaccharide sugar (i.e., it is composed of two simpler sugars—glucose and galactose). Lactose intolerance is the condition in which lactase is not produced so that lactose is not able to be broken down into the two simpler sugars. With this condition the lactose from milk and various other milk products remains undigested and causes an increase in the osmotic pressure in the intestinal contents. Consequently, water is “drawn” from the tissues into the intestine. At the same time, intestinal bacteria may act upon the undigested lactose and produce organic acids and gases. As a result, the person may feel bloated and suffer from intestinal cramps, diarrhea and gas.

Researchers at Lactaid, Inc., discovered a way to mass-produce the enzyme lactase. Lactase converts lactose into glucose and galactose, both easily digestible monosaccharides. The mass-produced lactase is formulated into the tablet product—Lactaid. The enzyme units in Lactaid are eaten by the lactose-intolerant person before or simultaneous to ingesting lactose. The Lactaid breaks down the lactose and then the person’s system can utilize the resulting glucose and galactose.

An external method to test the effectiveness of Lactaid is to find an organism that will only digest the simple sugars and not lactose. In this experiment, yeast is used as a test organism.

Yeast does not produce lactase and therefore, cannot digest lactose. (It is lactose intolerant!) Yeast can, however, digest glucose very efficiently. When it digests glucose, the yeast breaks down the glucose and produces CO2 gas as a waste product. This production of gas can be easily monitored. The absence or presence of CO2 gas production will be used as evidence of digestion by the yeast.



(for each demonstration)
Baker’s yeast, 12 g*
Galactose, 5 g*
Glucose, 5 g*
Lactaid™, ½ tablet*
Lactose, 10 g*
Water, 500 mL
Balloons, 4*
Erlenmeyer flasks, 125-mL, 4
Mortar and pestle
Water bath, 35–40 °C
*Materials included in kit.

Safety Precautions

Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information. 


Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. All solutions can be disposed of down the drain with an excess of water according to Flinn Suggested Disposal Method #26b.

Prelab Preparation

  1. Obtain all materials needed to perform the demonstration. The water bath is key for having the dramatic balloon expansion occur during the 50-minute class period. The demonstration will work without a water bath but at a much slower rate. A clear glass baking pan with hot tap water works nicely for this demonstration.
  2. Weigh out dry ingredients prior to the demonstration setup.
  3. Grind ½ tablet of Lactaid in a mortar with a pestle.


Review the summary diagram and then follow the steps after Figure 1:

{10337_Procedure_Figure_1_Summary of demonstration setup}
  1. Label each flask clearly as shown in the diagram.
  2. Place the dry sugars into each flask.
  3. Add 125 mL of warm (30–35 °C) tap water to the sugar in each flask.
  4. Swirl each flask until all the sugar has dissolved in the water.
  5. Add 3 g of yeast to each flask. Swirl each flask slightly to mix in the yeast.
  6. Add pre-ground Lactaid™ tablet to one flask containing 5 g Lactose, as shown in Figure 1.
  7. Place a balloon securely over the lip of each flask. (Be sure each balloon is flexible and not stuck together. Inflate each balloon at least once before placing it on the flask.)
  8. Place all four flasks in a water bath (35–40 °C).
  9. Observe the flasks for 20–30 minutes, checking each for the production of gas as observed in the balloons.
  10. Discuss the results and the effectiveness of Lactaid in the experiment.

Teacher Tips

  • This kit contains enough chemicals to perform the demonstration seven times.

  • Yeast does not have the enzymes necessary to digest lactose nor galactose, but it does have the enzyme to digest glucose. Therefore, the balloon in Flask B will inflate very effectively. The Lactaid will effectively digest the lactose in Flask D into glucose and galactose and then the yeast will digest the glucose to produce CO2 and inflate the balloon in Flask D. Flasks A and C should reveal no activity and the balloons should remain uninflated for the duration of the demonstration.

Correlation to Next Generation Science Standards (NGSS)

Science & Engineering Practices

Analyzing and interpreting data

Disciplinary Core Ideas

MS-PS1.A: Structure and Properties of Matter
MS-PS1.B: Chemical Reactions
HS-PS1.A: Structure and Properties of Matter

Crosscutting Concepts


Performance Expectations

MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.

Sample Data

  • This demonstration illustrates the functioning of Lactaid in a very unusual way. It answers some questions and raises many more. The demo can serve as a springboard for lab project extensions. How much lactose can a Lactaid tablet digest? Is it used up? Can it serve as a catalyst for a long time? What can speed up the reaction? What can slow down the reaction?

Next Generation Science Standards and NGSS are registered trademarks of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.