Is it normal for a beer to evaporate 1/2-3/4 gallon during primary fermentation?

I brewed an extract beer last week, an Imperial Rye IPA, and went to rack it into the secondary and then dry hop it. However, after racking it into the secondary, I saw that I had only 4 gallons of beer having left the yeast mass and other fermentation debris at the bottom of the primary (all of which added up to about 1/4 gallon). The OG was 1.080 and prior to racking it into the secondary it was 1.016.

Would it be bad to top it off with water in the secondary?

For reference the recipe I followed is here: http://beerrecipes.org/showrecipe.php?recipeid=1290

The "loss" could be due to thermal contraction, of you measured the volume when warm. If you lost that much to evaporation, you were doing it wrong and your yeast would be dead.

You can add sanitized (boiled and cooled water), but it's not worth the contamination risk. I would take what you got and move on.


Mylo

Thanks for the tip. I think the yeast is still alive though because I am still getting activity in the secondary. I'll just keep an eye on it. Thanks.

Depending on what you are using to measure your volumes, a 1/2 gal could easily be lost in measuring or marking errors. If you had any blow out that would contribute to loss, and technically you are losing some mass as the CO2 that is being generated (and as you mentioned the water vapor carried with it), though I doubt that would contribute volume-wise. I figure take what you can get and go with it.

Thanks everyone for the feedback. My friend and I let it just finish out on it's own and finally drank some on Friday. Came out well so I can't complain. As for measuring, the bucket we were using is premarked so that was what we using to gauge volume. However, I hear what you are saying regarding 'I figure take what you can get and go with it.' It's better to have 4 gallons of good beer then mess it up and have 5 gallons of crap.

Don't trust the measurements on those pre-marked buckets. I've found most of them to be off by a bit. I've remarked all mine and all my carboys. Add a measured gallon at a time and mark with a permanent marker. I also went back and put a half gallon mark in between the gallon markings.

For my glass carboys I use a paint marker since the "permanent" markers will eventually wash off. The paint pens I got from Home Depot worked great for this. Some of those were marked over 4 years ago and still are quite readable.

Keep in mind that there is about a 4% difference in volume of the wort between room temperature and boiling.

Wayne

Not that boiling water should go in buckets or carboys...