yeast move faster than you think?

I just had to share this. I try real hard to remember to get a sample for an O.G. measurement. I do all-grain, so usually at that point I am three beers into it so I have forgotten it several times. I ferment in a 6 gallon bucket with a bottom spigot. Last weekend I once again forgot to do it until after I had sprinkled a pack of dry yeast on top of the wort in my 6 gallon bucket, put on the top and an airlock. I am sure not 3 minutes had gone by when I realized I didn't capture a sample for O.G. So I figured, there was no way any of that yeast had propagated down (at least a foot?) to the bottom of the bucket, and I could draw off my OG sample out of the bottom spigot and all would be well. Then yes, I could have taken a reading right away since I had already cooled the wort. But I am in the habit of letting my samples sit (mainly because the first sample is usually pre-boil and needs to cool down anyway) to read later when the smoke has cleared. Anyway, many hours later I took my reading only to find out that my O.G. was lower than my pre-boil G, which of course is not possible since I had added no additional fermentables during the boil. Being confused about this I determined that the best course of action would be to have another homebrew, which worked reasonable well. Anyway the next night the sample had so much foam in it I couldn't measure anything and dumped it. My conclusion is, those yeast move really fast. Am I right?

 

They can move fast insomuch as reproducing then fermenting. Re-hydrated or starter yeast can start visible fermentation in a couple hours. But regardless, they do get To metabolizing those simple sugars right away.