prac class

[lainyv]

I have a year 11 class that are trying to do an experiment on alchohol fermentation. The one that I sat up isn't working as well as we hoped has anyone out there got one that they have used and know for sure it works...thanks for your input....lorraine

[rp]

Hi
Did you use a sealed side-arm conical flask in a waterbath with tube going into limewater?
Rhonda

[lada]

Just doing one now.
25g glucose
80ml water
2-3g yeast
few crystals of citric acid

Place in 500ml conical flask with rubber stopper with glass tubing going into Ca(OH)2
Leave in incubator at 30oC or warm place for a few days.

From time to time replace the lime water with fresh lot.
Good luck
Lada

[Xenon]

Old yeast can be a problem. I use the 7g packets for Coopers home brew; high turn-over means its usually fresh, plus its not too fussy if it gets a bit hot.

[smiley]

After a few misses I always sterilize everything with Sodium Metabisulfite every time.

[Labbie]

After a few misses I always sterilize everything with Sodium Metabisulfite every time.

I have heard of this before, which strengh 0.1M or more do you use? Do you recycle it, or disposal of it straight away? I do not have any here, but remember using it in the other school.

[smiley]

Sodium Meta... is always at its best when purchased fresh. So I get a small amount each time from the Home Brew shop. There are instructions on the side of the packet/bottle usually, but its really bucket chemistry. A few tablespoons in a big bucket of hot water, and submerge the items. Soak for a while, then drain and discard the solution immediately.

Works really well for sports bottles too. I do all my daughter's sports bottle about once a month - well maybe every 6 weeks.

[sunray18]

We have had good results this year - I use bleach solution to sterilise everything.. then rinse with distilled water. Make sure the yeast isnt out of date, and we just use the yeast and sugar .. We use buchner flasks - with the side arm, and plastic tubing which goes into a beaker of limewater.. I use parafilm to seal both the top of the flask and the beaker.We set them up using the lamps we use with Junior microscopes. This worked really well..

[MariaC]

Hi Guys, when you do this prac do you weigh the flask before and after fermentation to record loss due to CO2? We try this every year and the mass always increases not sure why, maybe the limewater gets refluxed up the tube when we take it off the heat and it all cools down. Any tips/ success with this prac? MariaC

[Ross]

We have found that to get the best results you use fresh boiled tap water. Boil the water and let it cool (or put it in ice bath to cool faster) to about 20 to 25 degrees before use. I have done data logging of the temperature rise when you have everything in a thermos flask and had a temperature rise of about 5 to 10 degrees. You can weigh the flask before and after and you should have lost a bit of mass.

[lada]

Maria, you are right. The lime water can be sucked back in to the flask.
We have it bubbling into lime for the one lesson, soon as it goes milky, remove it and stopper flask just with cotton wool. Use fresh yeast,
Lada

[Xenon]

You can check progress of fermentation with a hydrometer. A typical home-brew beer starts at about SG 1040 and finishes about 1010, and % ethanol can be calculated by finding the difference between these figures and applying a fudge-factor.
Of course, the brewer doesn't run the air-lock into limewater.

[ellice]

We put air locks (with limewater) on top of the flask. The air locks can be purchased from the home brew shops. Weigh the whole set up before and after.
Ellice.