Making Bacteria Media from Potato

Many Excellent Media are Made from Plant Material

By Harold Eddleman, Ph. D.

We call the food for our microbes medium (plural = media). In the early days, only kitchen foods were available for microbiological media. Potato dextrose agar is the most widely used medium for growing fungi and bacteria which attack living plants or decay dead plant matter. This page suggests media that a student can make in his home lab from plant matter such as potato, tomato, flour, cabbage, ssuu. Many species of bacteria and fungi require vitamins or factors from plants.

Microbiological Media derived from Plant Materials

Potato, carrot, tomato, rice, hay, grace, sllices, plugs, liquid

hay infusion, this was b025 the meat page; revise it for plant matter.

Text below is being used to plan this page.

Media derived from meat and its products are very common in medical laboratories because much of our knowledge of medically important microbes is based on the meat media. Actually most organisms grow better on media made from milk, but milk is white and it is more difficult to see the growth of microbes in milk.

If ground meat is soaked in water, the soluble proteins are extracted. When meats are cooked or roasted in canning factories, the juices are often sold in various forms for flavorings. Such meat extract was used by the early microbiologists for convenience. Nutrient broth and nutrient agar made from such products is the most widely known media to teachers and students. However, media based on tryptone are more complete and support the growth of more species of bacteria.

General Comments


You will often see the word Broth as you read the literature of bacteriology. You may have heard of Nutrient Broth and Nutrient Agar. They are very similar to classic Broth, but bacteria grow better on the genuine Broth you prepare at home from fresh ground beef. Classic Broth is mainly used for growing organisms from intestine or decaying meat.

  1. Mix 1 volume of fresh ground beef with 1 volume of tapwater and let stand overnight in refrigerator or room temperature.
  2. Heat to boiling, with stirring, to coagulate proteins.
  3. Filter through cloth. Discard the meat. If you worked cleanly and used refrigerator temperature for the extraction, the discarded meat is safe for human food.
  4. Add 1% peptone and 0.5% table salt (sodium chloride).
  5. Adjust pH to neutral using dilute NaOH (1.0 Normal is suggested)
  6. Heat to boiling again and filter thru filter paper if perfectly clear Broth is wanted.
  7. Dispense into tubes, plug with cotton, and autoclave.

That is the way professionals have made broth for a century. Such broth was used mainly for growing bacteria from human feces. Ground veal was sometimes used as some species grow better on the richer veal broth.

E Broth

Eddleman Broth is simpler for your home micro lab and many bacteria will grow very well on it, but the scum, sediment, and other results of bacterial growth will differ somewhat from the results on classic broth. Some bacteria grow better if you omit the salt. Salt (5 grams per liter) is used added if we are growing bacteria from human gut or decaying meat, but the bacteria usually grow fine without the salt. We will omit peptone because you don't have it. Use ground beef, or ground liver, or any kind of meat you wish.

  1. Mix 1/2 pound of fresh ground meat with 1 liter of tapwater and let stand several hours in the refrigerator, stir occasionaly to aid extraction of soluble proteins.
  2. Heat to boiling, with stirring, until the meat is cooked to coagulate proteins.
  3. Filter through a white cloth which is thick enough to remove all particles. Discard the meat. If you worked cleanly (clean pans and clean cloth) and used refrigerator temperature for the extraction, the discarded meat is safe for human food.
  4. Chill the broth in refrigerator so that the fat forms a hard floating layer. Discard the fat.
  5. Adjust the volume to one liter by adding tapwater.
  6. Do not adjust pH because you do not have a pH meter or pH paper and most bacteria will grow fine. If you wish add a 1/8 inch crushed limestone pebble to some of the culture tubes to see if there is any difference in growth of bacteria, or use powdered limestone or calcium carbonate.
  7. Dispense into tubes, plug with cotton, and autoclave in pressure cooker at 15 pounds pressure for 15 minutes. Let tubes cool in pressure cooker.

E broth will not give the same results as classic broth, but commercial nutrient broth will not give the same results either. Do not worry that you are making an inferior medium. E broth is what I often use. You need not remove the meat. The meat particles will buffer the medium and some bacteria will grow better, especially proteolytic Clostridium species. See LP liver particles medium.

Some Kitchen Foods Useful for Microbiology

Gelatin or Jello - can be used in tubes or plates to solidify medium or to test gelatin liqufaction

Potato Slices - Potato slices can be used as solid medium for streaking and isolating bacteria which are capable of growing on them.

PDA - Potato Dextrose Agar - is the best medium for growing many fungi, and bacteria and some yeasts. cook potato in P cooker, filter thru cloth. add corn syrup to make a lliquid medim. Add agar for solid medium

A word about agar. Agar is a gel from seaweed.. 10 to 15 grams is enough to sollidify agar. Use 7 gram per liter for soft agar. Agar comes from seaweeds and the gelling temp varries form 27C to 49C and Bact grade gells at 37C.

Carrot puree or carrot water is good for phytobacteria dnd fungi.

Starch will serve as carbon and energy source for many fungi and bacteria.

Sucrose is a c and E dource for fungi, and the bacteria able to hydrolyze it.

Red Cabbage juice is a pH indicator red in acid. I do not rememer the point where it changes.

Bacteria and fungi require a nitrogen source.

  • B023 - Making media (food) for your microbes from common kitchen foods
  • Vinegar or battery acid or Muricatic acid can lower pH of medium.

    Sodium carbnate or bicarbonate can raise pH

    DUST falls

    If you remember that dust falls or is blown by wind, you will have fewer contamination problems. Thus a loose foil cover or lid will protect a container from contamination. .

    Some items to sterilize and have on hand

    Safety Now. Don't begin this experiment until you have read my general safety page and the special safety notes for these experiments at the bottom of this page. Become a student who always works carefully and safely.

    Tube your medium and sterilize it.

    Record the results

    Suggested Further Experiments

    Most advanced microbial experiments require the use of solid media for isolation of pure cultures and the use of sterile medium. Pasteur accomplished much using selective methods, but he and others began using sterile medium and then rapid advances began.

    move page LINK for moremedia and steiliar;ona

    sterile toothpicks tostart rotten apples

    tyddalize milk 3 days in a row save a conrtol

    Safety Rules for Microbiology

    Safety First. Do not sniff moldy items. There is a chance that the spores could get into your longs and begin to grow. Certain fungi can grow in our lungs and antibiotics do not help much. Death has a good chance of occuring if you get infected by such fungi. I will write about the fungi later. Actually, one cubic centimeter of air in homes commonly has 5,000 or 8,000 particles of dust and some of these are mold spores including the dangerous ones. Each good deep breath contains about 20 million particles.

    Rule #1. Don't waste too much time wishing for equipment you don't have. Spend your time thinking about things you can do with what you have.

    I love working with bacteria, yeasts, fungi, protozoa, algae, and bacterial viruses at home. The study of these things is called microbiology. The study of all of them uses approximately the same equipment. Therefore, this series of pages B020 => B024 will concentrate on the supplies and equipment for studying bacteria. Later, I will write pages about the equipment to study the other organisms.

    You should read these pages in the order listed.

  • I might be helpful to read the first four pages before you do anything. The begin some simple experiments and you will learn what you need. Later you may want to buy some supplies, but at first see how much you can do with items from your home, farm, and gifts of discarded items.

  • First installed January 1998      Revision #2 1998 Feb 3
    Written by Harold Eddleman, Ph. D., President, Indiana Biolab, 14045 Huff St., Palmyra IN 47164
    | Indiana Biolab | Home Micro Lab | Bacteria Evironmental Needs | Food Microbiology |

    Expt 3. Autoclaved Potato slices. You won't have lots of success with gelatin media because in a warm room, they melt. Yet, solid media are so useful, the search went on. Potato slices are a good medium for some bacteria and many fungi. Great strides in bacteriology began when solid media were developed. Potato slices are prepared in a professional lab by putting slices in glass petri dishes and autoclaving. You can make your own dishes in many ways: You could use glass jars with loose lids. Try putting 1/4 inch thick slices of potato in a jar and then place it in a pressure cooker. Autoclave (cook) it for 15 minutes at 15 pounds pressure. Fiveteen pounds is the normal pressure for home pressure cookers. Of course you put jar cover on loosely before you begin autoclaving. Beside the potato jar, you could autoclave a bottle containing some tooth picks. Later you can use he sterile tooth picks to tranfer bacteria from colonies. Let it cool in the cooker, then remove. Open the lid of the jar in any room and let unseen dust particles fall into the jar for a few minutes. Replace jar lid loosely, and leave jar at room temperature a day or longer. You should see colonies of bacteria growing. Yellow colonies are frequent and orange may be found. The yellow colonies are often Micrococcus bacteria or yeasts. The oranage may be yeasts. I believe most od hese colored colonies are safe and ones for the beginner to study.