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MagicalMedic

Overcooked agar or liquid culture

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People often talk of 'caramelising' the sugars in agar or liquid cultures if you overdo them in the PC, and indeed if you do put them in too long the liquid or agar can go brown. It is often assumed or directly stated that this is bad and will destroy the agar / solution. I've also read however that dextrose / glucose is the main nutrient required by the mycelium in LC's - if this is true it seems odd that caramelisation would be a problem because the temperature for glucose to undergo pyrolysis (caramelisation) is 160 degrees C (as it is for sucrose and maltose) which cookers don't reach. For fructose(the most abundant sugar in most honey)the temperature is 110 degrees C, so it would caramelize in the cooker, but when sucrose undergoes pyrolysis it turns into fructose and glucose.

I read this all on wikipedia [https://en.wikipedia.org/wiki/Caramelization#Effects_on_caramelization], and I'm an amateur, so I could be way off re. the nutrient thing.

So what is actually degrading / decomposing when someone overcooks their agar and why is it bad?

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caramelisation may take place at 160 deg c at ambient pressure but remember that pressure cookers run at increased pressure hence why they are called pressure cookers. Pressure has a big effect on chemical reactions and a reaction that takes place under pressure will not have the same parameters as without pressure.

So what is degrading depends upon what you are putting into your agar and it is bad because the fungi your trying to culture can't make use of it.

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Sugar carmelization

With Karo and Honey, if you PC for too long your solution may turn yellowed. This is called caramelization and is over-baking of the sugars which may result in little or no growth at all. If this happens you can still try and grow a culture in the caramelized sugar jar, but if you are pressed for spores it is best to just start over. This is something you want to avoid. Liquids don't take very long to sterilize so you don't get any benefit from PCing for longer than 15-20 minutes max.

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a reaction that takes place under pressure will not have the same parameters as without pressure.

 

There it is! Thanks man my bad, I totally overlooked that.. forgetting my chemistry :drool2:

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More for interest's sake, but worth adding, you can actually overcook agar. If you heat it up too high or for too long you can hydrolyse the agar and it won't set. Back in the day agar was generally sterilized by successive cycles of heating with steam, then cooling, then heating etc (called Tyndallization). This also eliminates the possibility that any sugars will be caramelized.

Autoclave/pressure cooking is much faster though :)

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With LC using distilled water will really help to keep it from caremlizing.

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i use rice malt extract for liquid cultures it seems to be able to handle the high temps and stays pretty much crystal clear i ad some colloidal silver and h202 when i can see a little growth

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