if yeast and sugar make alcohol and carbon dioxide, what else is left behind?

Question

i just find it hard to belive that sugar(solid) and yeast(solid) mixed in water(liquid) will produce carbon dioxide(gas) and alcohol(liquid).....
just seems like something else should be left in the equation? i'm not a chemist... just seems it cant be that easy... is it?

what do you mean sort of? it IS really that simple or is it a 3 year course in chemistry?

Answer 1

Richard already answered the question, but maybe this will add something.

Here's what a chemist of 150 years ago would have done.

Weigh some water, yeast and sugar into a container that won't let the water evaporate. Put a balloon over the container and capture the gas that comes off. When your fermentation is over, weigh the gas in the balloon and send it out for analysis (our 150 year-old chemist would have had to do it himself). It will be carbon dioxide. Warm the fermented liquor and capture any gas that comes off below, say, 60C. It will be carbon dioxide with a little alcohol and a little water. Heat the liquor until it just starts seething and capture the gas that comes off by cooling it back to a liquid. It will be alcohol and water for a while, eventually becoming just water. Filter the water that did not distill and weigh the dried solids on the filter paper. It will weigh about as much as the yeast you put in. Analyze the filtrate for sugar. If there is more than a trace, distill the remaining water to leave a syrup residue.

Since the reaction of sugar to make alcohol and CO2 consumes some sugar, the leftover sugar will weigh less than the sugar you added, by just enough to account for the alcohol and CO2 you recovered.

Then you've accounted for all the starting materials and products and the weights of everything you started with will equal the total weight of the products. That's how the proof was worked out.

One more thing...it is a simple as that, but understanding and controlling it could take a lot more than 3 years of chemisty to achieve.

Answer 2

Sort of that easy.

The yeast provides the enzymes which promote the rapid conversion of glucose (the sugar) to Carbon dioxide and ethanol. You will end up with yeast in the final solution (plus some dead yeast which will fall to the bottom of the container.

Baker's yeast will work, but brewer's yeast with withstand a higher alcohol concentration before it dies. If the solution is capped before it is finished, the solution will "bubble" upon opening. This is how "sparkling" wines and beer is made.

Commercially, the fermentation is done in a vat and the top solution is siphoned off into bottles, leaving the dead yeast in the bottom of the vat.

Answer 3

dead yeast is the sediment at the bottom of the container,
probably some sugar left over if you're making wine, etc.