I have lots of beginner questions

I just got a home brew kit for Christmas and I finally had a chance to start my first brew. I am totally lost when it comes to science, so I have a few basic questions First: What the heck is gravity and what does it tell me about the brew? Are there any other Stats that I should be keeping track of?

Second: When I was trying to put the bubbler thing on my fermenting bucket, the plastic gasket fell into the batch. I reached in with my hand to get it. Will this mess up the beer? How will I know if my beer is contaminated?

Finally, how important is it to prepare the yeast in warm water? I just put the yeast on the top of the wort for ten min then stirred it in.

Thanks for your help.


IPA

All simple questions asked and answered a thousand times just last year alone I am certain, but...

Q: What the heck is gravity and what does it tell me about the brew?
A: Water has a gravity of 1.000. Any sugars (malt is sugar) added to the water produce gravity. The more sugar, the higher the gravity. When you brew a batch of beer you'll (generally) use between 5 and 8 lbs of malt. each pound adds gravity, but this is relative to the amount of water present. The less water the higher the gravity. The more water the lower the gravity. For example, (these numbers are for quick math purposes) you may get an OG reading of 1.040 on your hydrometer. After you add yeast and the wort ferments your gravity may be 1.010. If your attentuation of your yeast is 75% then you have beer...1.040/75%=1.010 (or 40/75=10).

Q: Are there any other Stats that I should be keeping track of?
A: Too numberous to list here. Your input will vary from others. Take many notes especially of everything you do or add to the pot.

Q: ...the bubbler thing on my fermenting bucket, the plastic gasket fell into the batch. I reached in with my hand to get it. Will this mess up the beer? A: Depends, did you wash you hands after last taking a leak, or ...

Q: How will I know if my beer is contaminated?
A: Tough question to answer as some yeast produce a lot of sulphur...think farts. It'll smell bad, but it's all good.

Q: Finally, how important is it to prepare the yeast in warm water? I just put the yeast on the top of the wort for ten min then stirred it in.
A: With dry yeast it really doesn't matter. Stirring is not necessary.

Thanks for you help. How do you find the alcohol content using the gravity? Is there any other information about my beer that the gravity will tell me?

someone can correct me if i'm wrong...but i believe you can get a good indication of your alcohol by volume (abv) by substracting the final gravity reading after fermentation from the original gravity reading (before you pitched the yeast)....so if the OG was 12% (on the hydrometer) and the FG is 5%, then you can approximate that you have 7% abv...again, i'm new too but i believe this is what the instructions said that came with my hydrometer....and...be sure you correct your reading for the temperature which you took it at...a good chart for this conversion can be found at...

http://www.howtobrew.com/appendices/appendixA.html

Abw = 76.08(og-fg)/(1.775-og).

*edit* wow that looks confusing..

Using the same numbers...

OG 1.040
FG-1.010

40 - 10 = 30

30 x 105 = 3.15% ABV (alcohol by volume)

3.15 x 1.25 = 3.937% ABW (alcohol by weight)

Thanks for all you help guys. I will let you know how it turns out!