I just tried to clean out a 6.5 gallon carboy that I had used for primary fermentation. First, I hit it with hot water and dumped it out. Then, I put about a half-gallon of hot water with some dish soap. No more than five seconds after I began scrubbing the carboy with an angled brush, there was a loud explosion, and the carboy broke into four pieces in the sink. The temperature of the beer was around 60°F, and the temperature of the water was about 125°F. What, if anything, did I do wrong? Was it just a bad carboy or did I commit a fundamental mistake? What is the proper way to clean a glass carboy?
I think that any rapid change in temperature can explode glass.
The same can happen to a drinking glass that you pull out of a hot dishwasher then add cold beer. It can crack and possibly explode.
I am not saying that all glass does this but in some cases it can.
I have to say, I am surprised by this. I'm glad you brought it up.
I think the temperature gradient could have been the problem. The bottom with the water was rather hot and the top was cool causing stress over the long length of the bottle.
On the other hand, I'm surprised that the gradient caused by hot tap water and cool but not cold air temperature would have been enough of a shock. I wonder if there was already a crack or something.
On the other other hand it's been my observation that many glass carboys these days are somewhat thin in relation to their size these days and so are not as robust. I compare this to glass cooking bowls that are thicker and smaller than a carboy and so are able to withstand boiling water being dumped in them. Also, the glass in cooking bowls is possibly of higher quality.
Something to watch out for as I bottle my weisbier and clean my 6.5 gal. glass carboy. :-(
Here's a possibility: I remember in physics labs some students would wrap especially large glass flasks and glass thermal bottles in fiber reinforced tape so that if there is breakage at least the mess and the danger was somewhat contained. In our case it might spoil the look of our beer in the carboy but it might be worth it. Or maybe there is a plastic web sleeve or sock we could get (google carboy shield).
I bought a glass carboy for the same reasons as you. however I quickly discovered I can buy about 6 buckets for the price of 1 carboy and they are WAY easier to clean. My glass carboy is now filled with about 4 strands of blinking colored Christmas lights and sits on top of my fridge on the patio. As soon as my Keezer is done (hopefully this weekend) it will have a new home :)
Never clean glass or plastic carboys with hot water and soap. Use a proper cleaning agent like Straight A or PBW (Powdered Brewery Wash). I have a no scrub method where I use PBW in my carboys and soak them overnight or longer. You can use PBW repeatedly without it losing effectiveness so generally I leave it in the carboy until I'm ready to use it again and then transfer it into the next carboy that needs cleaning. All the hop material and yeast that form a ring around the top of the carboy falls out and the carboy is ready for use after properly sanitizing it. No scrubbing or carboy brush is necessary.