Making a Hay Infusion

It is possible to enrich microorganisms such as ciliates by making a hay infusion. Generally one should be very careful when making a hay infusion, as the bacterial concentration can become very high. The procedure is presented here for educational purposes only. If the hay infusion starts to turn cloudy, then this is an indication of a high bacterial concentration. In this case the ciliates were not able to keep the bacterial count low.

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A hand full of hay, a large beaker, pond water, some milk


  1. Take a hand full of dried grass or hay (free from pesticides or herbicides) and cut the grass into smaller pieces
  2. Place the cut grass into the beaker and about 0.5-1 liter of water.
  3. Add 1-2 drops of milk. The water will turn slightly turbid. The milk is food for the bacteria and they will start to reproduce. The ciliates feed on the bacteria and will also reproduce.
  4. Let the beaker stand open for several days, protected from direct sunlight as this may result in overheating and the heat will reduce the oxygen concentration. Do make sure that the beaker receives sufficient light, though. Photosynthetic algae present in the pond water will produce oxygen.
  5. Keep adding 1-2 drops of milk when the turbidity disappears. Bubble some air through the water at regular intervals (using an air-pump from an aquarium) or agitate the water a bit to enrich it with oxygen.
  6. Replace the evaporated water.
  7. Take some sample from the surface of the water (where there is oxygen) for microscopic investigation. If the water is agitated, then the microorganisms are (of course) not able to collect beneath the water surface.


Problem: The water starts to smell.
Solution: This is normal. Bacteria are starting to decompose the hay and the added food. If bubbles start to appear though, then this is an indication that methane is formed anaerobically. This should not be and indicates that there is not enough oxygen in the water.

Problem: There are many bacteria but too few protozoa in the water.
Solution: Probably there was overfeeding. Add less milk and less hay. The bacteria multiplied too quickly and the protozoa could not keep up.

Problem: Nothing much seems to happen after a few days
Solution: Did you use chlorinated tap-water? Was the hay treated chemically?

Safety issue: You are cultivating unknown microorganisms. Potentially harmful bacteria could also be in the sample. It is therefore important to observe the rules of hygenics. Use this method at your own risk.

One thought on “Making a Hay Infusion”

  1. Thank you for this procedure for Hay infusion. I hope we’ll do great at laboratory today.:)

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