No Original Gravity Reading

Not necessarily. you know what you mashed and you know the expected attenuation of your yeast so you could get a pretty good idea if you were at terminal gravity. This of course depends on whether your efficiency is consistent.

If you brewed with extract you could have an extremely good idea

 

A reading now would tell you what the attenuation is now. A reading three days from now would tell you whether fermentation is complete--ie, if it hasn't changed in three days, it's done, and it's ready to bottle.

Also, I would suggest: never, ever be in a rush anything in brewing. Especially not bottling.

 

If you have a refractometer as well as a hydrometer, there is math that could get you back to your OG. But it's not trivial. If not, you'll never know what your OG was, but you'll still know when attenuation is done. Gravity readings that don't move tell you that attenuation is done. Just knowing your current amount of attenuation does not.

 

Bottle when gravity has stabilized.

 

I have occasionally blown off the OG reading on a recipe I make many times per year, which involves a beer that starts out well below 1.050. That said, I never blow off final gravity readings, which are all you really need to know if the beer is ready to bottle.

 

I've skipped OG a number of times (not nearly as many times as I've forgotten the Irish Moss, but that's another story). As VikeMan said, a refractometer combined with a hydrometer will give you the OG.

 

At this point I would not even worry about the OG, at least as far as determining whether the beer is finished fermenting. Use you hydrometer or refractometer to determine this. If you post your recipe, we could give you an idea of what your OG was.

 

Fwiw, OG is not necessary to know if fermentation is complete. Once the gravity stops changing, it's done, no matter what the OG was. It's only necessary to calculate the ABV. I wouldn't sweat it.

 

I've forgotten the OG more than once. It's not that big a deal unless (1) you're way off in the first place, or (2) you're anal about collecting data. Stabilized readings over successive days indicate completed fermentation. OG helps calculate stuff, but not that. No matter what the readings, don't even think about doing anything with your beer till it has been in primary for at least two full weeks.

 

If you have the FG and an average of the apparent attenutaiton value in your brew shed...you could come up with a reasonable estimate of the OG.

 

That's why all my bottles are floating in mid air...

 

This must have something to do with you living in the mountains and being farther from the planet's center of gravity than we lowlanders. Good thing you are not nanobrewing, as some of the laws of physics get a little screwy
at that spatial scale.