Overshooting mash temp ? What's the result

With my relatively new HERMS system I built, I still have not got the PID sorted out and working properly.

The result is that I sometimes overshoot my 68 C mash temp target by 3 or 4 degrees for a short period of time - say ± 10 minutes during the mash.

My question is, will this result in the whole mash being denatured making the sugars and starches unavailable for fermentation or just of small percentage of the total available sugars ?

Bottom line is, is this a big deal ?

Any guidance appreciated

Should be okay as long as you are not 77+ C.

It might impart a bit more sweetness to the beer.

More info here: http://braukaiser.com/wiki/index.php?title=Starch_Conversion

So would it be better to undershoot then raise the temp slowly ?

Generally speaking, yes. While that may lead to a slightly drier beer, the effect isn't likely to be significant given the time periods involved.