Using a Hydrometer

How do you extract a sample during the fermenting process to take a hydrometer reading? Is it ok to pop the lid at any time during fermenting to take a quick sample or will this contaminate the beer? I've read some people use a Turkey Baster or something like a 'Wine Thief'. I'm just not sure when/how to use these??? Any help??

Opening the lid is fine. Keep as much sanitized as you can (I keep a squirt bottle filled with starsan solution for just this purpose). No need to stir, just open up and pull your sample.

I like my wine thief but have used a baster in the past. They both work.

You will want to calibrate your hydrometer anyway, so fill whatever tube you're going to use with distilled water and test your hydrometer. After you remove the hydrometer, mark the level with a sharpie or something so you know how full the jar needs to be. I use this jar from Northern Brewer:
.
because it is very easy to clean and it costs less than $5 Use your baster or wine thief to fill the jar to the mark and you won't have any spillage or extra waste.

Oh...and I just store my hydrometer in that tube under the sink. I haven't broke one yet.

It's ok to take a sample whenever you want to, or need to, as long as the utensil is sanitized before sticking it in your beer.

I usually don't take an SG until at I'm planning on doing something with that reading. What I mean is, if I'm going to let it sit for another week, no matter what the reading, then I don't bother taking a measurement. If I want to check the SG to see if it's ready to bottle in a few days, or ready to rack, then I go ahead and take a sample. You want harm the beer by opening it and taking a reading.

Thanks guys. Exactly what I was looking for. I won't plan on taking a reading until I'm checking if it needs to be bottled.