I am new to homebrewing and am getting help from an experienced brewer. So far I think everything has gone OK. I am doing all-grain brewing on a stovetop. I have done 2 brews. I am doing the mash and boil in a 15 gallon kettle. As far as the mash, I have had no problem hitting my target saccharification rest temp and can hold it there (within about
+- 3°) for 60 minutes. However when attempting the boil I have run into somewhat of a problem. I can't quite reach a rolling boil. I can only hit about 210° with the lid off. And over the length of the boil, the temp slowly decreases to about 205°. If I leave the lid on, I can hit a nice rolling boil. For future brews, I plan on having a smaller amount of liquid in the kettle and will leave the lid on. Once I noticed I can get a much better boil with the lid it was too late to brew that way because I had about 6.8 gallons in my kettle and needed some of it to evaporate so I can get down to about 5.5 gallons.
So my question is this: What are the chemical, taste, etc. consequences of doing a "weak" or "light" boil at about 210° ? Will I taste a difference? Would an experienced brewer taste a difference? Was it not 100% sterilized?