Some good, some bad, but on balance a great idea
I have been looking for an easy way to make starter wort in advance to simplify the process. I looked into using canning jars, but that required a pressure cooker and related canning equipment that I don't have. I thought about using canning jars without a pressure cooker, but was too concerned about a possible infection. While it was available, I used the FastPitch canned wort which was great, but it is no longer available. Then I discovered these bottles and thought I would give them a try.. I bought two for starters (pun intended) and made my first batch: mix DME with water in measuring cup, pour into bottle, add fermacap to prevent boil over, place in microwave for 6-7 minutes until it boiled, remove from microwave (use oven mitts), cap and place in refrigerator. Voila, ready to use starter wort. When it was time to make a starter, I just removed the bottle from the refrigerator and let it warm up to room temperature before using.
I made starter wort with my two bottles a number of times without any problems or infections. However, a few weeks ago, I was making a new starter wort when the bottle exploded after I put the cap on. I had microwaved the starter wort as usual, however, this time, I had a slight boil over in the microwave. I removed the bottle from the microwave, put it in the kitchen sink, put the cap on and then ran some water over the outside of the bottle to rinse of the boil over wort. BOOM! The bottle shattered into 6-8 large pieces. I know it was probably foolish to rinse the hot bottle off with tap water, but I expected it to be able to withstand the temperature change. Live and learn.
Despite the explosion, I ended up buying 2 more bottles and just finished filling them with starter wort without any problems. The convenience is worth the risk in my opinion. However, I will never run tap water over a boiling hot bottle again, even if it is borosilicate.