I've got the same problem. I guess it's *really* common with twins. As someone said to me, if you'd had to share everything with someone for your entire life, you might want to bite them too!
Your kids are a bit older than mine, so I would definitely talk about it a lot. I have found that I am able to tell when Henry is in a "biting mood." During those times I stay really close and catch him before he bites her. I also break up roughousing or even hugging and kissing before it turns into a bite. I wish I didn't have to, since the hugging and kissing is SOOOO cute, but I've been burned enough times that I'm going to be careful for now!
As for the tobasco and the lime juice, I wouldn't do it. That's a form of physical punishment, and unless you put the stuff on her arm (and I *don't* recommend that!) it won't be a direct consequence. It will just teach him that physical punishment is an appropriate response to something you don't like. My 14-month-old is able to understand that biting is a no-no, he just doesn't have the impulse control yet. When he does it, I comfort DD, then I get right down in his face, make him look me in the eye, and tell him very seriously that biting *HURTS* his sister, and that he shouldn't do it. Sometimes if he's still riled up (biting moods are usually kind of hyper, riled-up moments) he'll laugh, but then I'll tell him again how serious it is. He will usually shake his head "no" when I'm telling him. I found that the biting got much better when he started shaking his head no--he was finally understanding.
With an almost-two-year-old, I would think you could stress the empathy angle more--"hurts sister--makes a boo boo." Henry's a little young for that right now (though I do it, with words and signs), but what I do when he bites me (yup, he bites us too) is to put him down squarely and uncerimoniously and walk briskly away, saying "I don't like to play when people bite me." That's a natural consequence for biting--not having the bitee to play with anymore. As he gets more verbal (if it doesn't stop by then, please goddess!), I will talk to him about what he was trying to communicate when he bit and give him words or signs to help him figure it out. Today he was trying to initiate play with an older child and was pulling her hair. I gave him suggestions as to how he might tell her he wanted to play with her and he actually followed one of them (give her a toy to play with)! Try to figure out what he's trying to *say* with the bite and then help him say it appropriately, either verbally or non-verbally.
Finally, is he teething? We get a new bout of biting whenever Henry is cutting a new tooth (and when Eleanor's teeth are getting really bad, she often joins in and bites back!). Maybe he's getting his 2-year molars? We do use painkillers with our kids, and we have started to take biting as an indication that they're in pain. Perhaps you can add to your firm talk about it a question about whether his mouth is hurting and then give him choices about how to deal with pain in his mouth (tell mommy so she can give you tylenol, chew on a teething toy, eat an apple, etc.).
Good luck to you with this. Biting is one thing that can drive me up a wall faster than anything else, so I hear ya sister!