Yeah, I'm going back-and-forth on this one. I was going to say that I would use the plural in your second example, and, certainly, it would not be considered "incorrect" by any style book or grammar pedant, as "bratwurst" isn't a mass or collective noun.
Or is it? I started to think about it. I have heard constructions like "Is the bratwurst on the grill" used in a collective sense. I think the more prescriptive types might have an issue with it, but, in my experience, the word is used in both countable and non-countable senses. That said, with the modifier "several," in your example, my natural inclination would be to use the noun with the standard plural marker, i.e. "bratwursts," just like I wouldn't say "I put several meat* on the grill."
On the third hand, I can see "bratwurst" being internalized as an irregular plural by some speakers, which I think would be the correct analysis if speakers do find constructions like "I put several bratwurst on the grill" to be grammatical.