Face it, making beer can make you paranoid. Everything has to be spotless and sanitary. The boil has to be watched carefully to ensure that the new brew isn’t scorched or doesn’t boil over. Hops have to be added at just the right time. Temperatures have to be monitored so that the delicate new yeast can catch hold, grow and thrive. We worry about oxygen levels. The temperature needs to be consistent. Sunshine is the enemy.

So, after cleaning, sanitizing, boiling, cooling, oxygenating and pitching, we find a warm, dark, safe spot for the immature beer, and we lovingly seal it away hoping that all is well. At this time, the thing most likely to horrify us is the thought of bacteria, because we know that bacteria are evil little freeloaders who have a sadistic desire to get into and destroy our delicate, helpless beer

After the brewing is done, after the pots are scrubbed and the cooking tools put away (and after we check the airlock even though we know nothing is happening yet), we sit back, relax, and have a home brew. We check the airlock (again) before going to bed and feel relieved satisfaction to see the beginning stages of fermentation. But the next day, when we get out of bed and check our fermenter, our cautious satisfaction crumbles. We experience a moment of stunned disbelief when we see that krausen has crawled out of the bucket! The lid has blown off of your fermenter (or the airlock has shot out of the top) and there is a gaping hole between the safe confines of the fermenter and the bacteria infested air.

We immediately assume that at some time while we were sleeping, bacteria climbed into our fermenter and is now merrily slaughtering the yeast and altering the taste of our beer. We become frantic to find a way to save our beer even though we are secretly convinced it is doomed.

You already have all the facts regarding this particular fiasco, you just haven’t realized it. Now is a good time to take a deep breath and review the basics (right after you frantically snap the lid back on the fermenter). Your beer is going to be fine.

yeast + sugar = alcohol & carbon dioxide.

When carbon dioxide is being produced at a rapid rate, it sometimes pushes the top of the fermenter off or blows the airlock out of the lid, but just because there has been a breach in fermenter security does not mean that the yeast has stopped doing its thing. The yeast is still munching away, growing, thriving, multiplying and most importantly (at this point) producing more carbon dioxide. That means that there is still a light but persistent push away from your beer and out of the fermenter. Most of the time this is sufficient to protect your beer. Why? Because bacteria floats, and the carbon dioxide breeze moving away from your beer is a very effective barrier.

Also, it’s important to remember that yeast and bacteria are natural competitors; they both eat the same things. Bacteria generally multiply at a much faster rate than yeast which is why protecting against bacterial exposure is especially critical in the beginning stages of the process. But if the yeast has managed to blow off your lid or airlock, you can be confident that at this time the yeast is strong, healthy, well established and multiplying like crazy. Billions of yeast have a pretty good chance of making sure that a couple of stealth bacteria cannot establish themselves sufficiently enough to affect your brew.

So if you discover that the top of your fermenter (or the airlock) has blown off, try not to worry too much. It’s unlikely that any spec-ops bacteria have managed creep past the defensive barrier of air-flow and carbon dioxide. Even if a couple of particularly diabolical bacteria have managed to use ninja skills and avoid the carbon dioxide barrier, you can comfort yourself knowing that the yeast has effectively claimed your beer as its territory and it won’t be taking kindly to strangers.

One final note: Just because your yeast may have managed to discourage the growth of bacteria in this instance, do not assume that your beer is safe forever more. Once high krausen is a thing of the past, bacteria can easily invade and overtake your brew. Your yeast has partied hard and will again become too weak to protect itself so continued protective measures (ie sanitization) remains critical.