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Thread: How many days can you keep yeasts in a broth before they die

  1. #1 How many days can you keep yeasts in a broth before they die 
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    Uh, ive isolated this yeast culture from soil and the broth i used to cultivate it in is a glucose yeast peptone broth in a 1 Litre EFlask- i was wondering if anyone could tell me how long i should keep it in the broth, or how to cultivate it using a broth medium. i was planning on just adding a certain amount of broth each day; someone help please :P, i dont know when to tell if the yeast cells are dying out. they formed a sort of biofilm on the sides of the flask after three days...how do i know if the yeasts are dead?


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    Forum Professor marcusclayman's Avatar
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    I don't know how scientists do it, but I'm a hobbie baker

    yeast is dead when it nolonger proofs

    to proof yeast mix some with 90 degree(f) sugar water, wait 5 minutes for it to foam


    I don't know how to get yeast from soil, but unless your doing something with soil specific yeasts, it may be easier to get from sourdough starter.


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    how much does it foam? i tried putting some sugar water before, and it sort of bubbled after a few hours. my problem is knowing how long to keep it sitting in the broth(culture mix)- i dont know when to tell if the yeasts have consumed the nutrients/start dying. i added 200mL of the broth the other day and it started smelling like fermented bread after a few hours.
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    They're sturdy buggers. On solid media they survive for months. Try making some agar plates or slants. I'd be more concerned about bacterial contamination, meself.

    http://brewery.org/library/YstCult.html
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    my professor is aking me to cultivate them in broths for wort fermentation and im scared that the increasing turbidity might mean theyre multiplying too fast/not getting enough food. i include 1mL of 1% antibacterial per 100mL so i wouldnt worry about bacterial contaminations. ive kept the yeasts in the broth for about 5 days now... how do i know theyre not dead? XD
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    Forum Professor marcusclayman's Avatar
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    that smell is a good sign that they are alive and feeding

    if you don't smell anything, and nothing is foaming; either they are dead, or they are dormant

    either use a microscope to see what's going on, or a litmus paper to measure alcohol content... eventually, with too much alcohol(waste from feeding) they will kill themselves off; and if you do the maths, you may be able to figure out how much alcohol is equivalent to how much food consumption, and determine how much food is left.

    note: different yeasts can withstand different alcohol contents before dyeing
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