Starbucks needs to do everything it can to improve its image as a purveyor of premium coffee. The move towards pre-grinded coffee beans and automatic espresso makers left it vulnerable.This is a little surprising. Historically, it's not unusual for irregular/strong verbs to move toward using the regular/weak pattern, which consists of whacking a -d/-ed ending onto the stem. (And no sound change.) We use this pattern in new verbs pretty much without exception. And we see it when a traditionally irregular verb is used in a new way that is sufficiently different to cause users to "forget" that it has an existing irregular past tense. (Examples frequently cited, including by me, are to fly out; to grandstand.) You can sense when verbs are teetering between irregular and regular, as I've noted before: what's the past of to troubleshoot? What about of to cheerlead?
What's surprising about grinded here is that the usual past tense -- ground -- is in constant use even in this context. People talk about fresh-ground coffee and about dumping the grounds. But perhaps that pre- threw off the writer; if we give him the benefit of the doubt here, he's analyzing to pre-grind as a new verb (to pregrind, let's say), and new verbs always take -d/-ed.
It's a mistake, from a purely editing perspective, but it's one that follows a rigid pattern, so to speak. If a body is going to get the past tense of to grind wrong, odds are that they'll get it wrong in exactly this way.
So, Google. The search grinded +coffee yields
Grinded still sounds odd to me, but to quite a few people, apparently it does not. (Is it more prevalent in writing than in speech? That's a question that we here are not equipped to research, alas.) Let's check back in 20 years, see how things are developing.
Update (5 June 2008): Found this in a blog today: "While there was some discussion of how to fix the problems, it got overwhelmed by grinded axes swinging wildly against certain personalities in Microsoft India leadership."