What is the usual procedure for measuring gravity? Is it typical to just take an original and final gravity measurement or should measurements be taken throughout? I've heard people talk about taking readings throughout the process to dictate where the beer is at; do they just drop their hydrometer into their carboy and leave it there throughout the brew or do they risk contamination by taking samples out? Also, do I need to record/account for exact temperature when I take readings?
I don't take readings throughout fermentation but some people do. There is an increased risk in collecting samples, but if your sanitation practices are good, the risk is low. I don't recommend dropping the hydrometer in. It will hard to find among the krausen, will be very difficult to read accurately, and the reading will be slightly off due to co2 that is dissolved in the beer during fermentation. For an accurate reading you should know the temp within a few degrees. My procedure:
- Sanitize a turkey baster
- Fill a Glass or mug with wort/beer using the baster.
- Pour wort/beer between 2 glasses to remove dissolved co2 (I don't always do this but it will make readings slightly more accurate)
- Pour into hydrometer test jar.
- Take temperature reading.
- Take gravity reading
- Take 2nd temp reading for an average temp.
- Correct gravity reading for temperature.
- Sample beer, do not add back to Carboy/bucket
You can take measurements throughout fermentation to find out how fermentation is going. I would recommend a wine thief.
Just sanitize it before you stick it in your fermenter.
I generally just check gravity readings when I'm racking from primary to secondary and from secondary to keg so that I can just siphon into my hydrometer tube - whatever you call those things.
If you obsessively check, you risk contamination, and I'm not sure that the extra information is really telling me anything aside from, "Yep. Not done fermenting, yet." and you can usually tell that by eye.
I also suggest getting a hydrometer with a thermometer built into it so that you can just check gravity and temperature readings at the same time. They're not the most accurate things, but they're close enough for the inexact science of calculating gravity.
Finally, if you spin your hydrometer in the tube while you're measuring gravity, it'll shed any CO2 that may be lifting it for a few moments so that you can get a fairly accurate reading. No need to totally de-gas the liquid.
My friend @ruinationpress recently asked me about another solution. Austin Homebrew has a "specialized" Wine Thief that has been altered (so they say) to allow a hydrometer to sit inside. This allows you to put a sanitized thief in the carboy (assuming you're using a carboy), check the gravity, and pull it out, without removing wort / beer at all.
I don't know if this is actually a good idea or not, but I didn't think asking a question about this product itself would be worth it. So, here's another answer for measuring gravity.