Student Post-Experimental Advice

Przemko przemko at
Tue Feb 8 09:13:12 EST 1994

>My sons fourth grade science project is to test which sandwich spread will
>grow bacteria the best and we need some scientific advice.
>Materials and Methods
>The experiment is spread mustard, ketchup, mayo, jelly, peanut butter, butter,
>horseradish on a separate bread slice. The control is a bread slice without a
>spread. The experiment was done in triplicate one set was left at room
>temperature exposed to the air, one set was place in a ziploc then left at room
>temperature, and one set was placed in a plastic container then refrigerated.
>After four days we visually observed no bacteria, no fungus, nothing!
>We then sampled each spread by plated on LB agar plates. Only peanut
>and peanut butter(bag) developed bacterial colonies. No colonies were detected
>for butter or mayo? We expected positive results for butter and mayo.
>The question is what bacteriological test could we do to better detect
>bacterial growth?
>Any advice would be welcomed.
>Thanks DPSMITH internet:smith_dennis_p at

Very nice project. The scary part is that nothing grows probably
because it contains a lot of preservatives and other additives that
will prevent growth of anything.That reminds me an experiment
that I did at some point in the past. I compared milk from your local 
Jewel/Safeway?whatever-you have-locally to milk from a belgian
supermarket to milk from a farm.
The results were as follows:
milk from the farm got sour in 24h
milk from belgian supermarket got sour in 5 days
milk from an american supermarket got sour in 11 days and even then was
not really sour but something weird grew in it.
All this is probably due to different techniques used to preserve milk or
butter or mayo or whatever else you put on bread.
Try an organic spred with no antibiotics and other crap and then see the
You could even make your own mayo- a small science project on its own
(emulsions etc.)

Just my 0.02$


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