Could by any of a number of causes -- maybe all of which you have run through
- -- but they fall into two categories: a) The paddle isn't moving the
ingredients around sufficiently, or b) you're weakening your yeast or it is
If the Hitachi will run with its top lid open, start the machine without any
ingredients and reach down with a rubber spatula and try to resist the
turning of the paddle. It may be that your clutch is slipping and that is
just won't agitate a mass of goop. On some models, similarly, the paddle
couples to the motor shaft with a pin or key that could wear or break. In
that case the paddle would appear to turn, if simply observed, but would slip
when it met any serious resistance.
Our experience with Fleischman's yeast hasn't been all that great and we buy
ours now in bulk from a health food store, store it in the fridge in a
tightly sealed glass jar and don't even bother to let the one or two
teaspoons full reach room temperature before putting them into the machine.
You might want to 'proof' a bit of your yeast by sprinkling a little over
luke-warm water to which you have added a dash of sugar (for food). It should
become foamy within 10 minutes.
The King Arthur Flour folks caution that salt will weaken the action of the
yeast, so we make sure that the salt and water go in first, then the flour
and other ingredients, and the yeast last (or the other way about, if your
machine calls for reverse order). The middle ingredients serve as a buffer,
keeping the salt away from the yeast until a bit later in the mixing cycle.
A long shot, but a high level of chlorine in the water will weaken or even
kill yeast. This seems to be more of a problem with the wild yeasts so
important to the sour doughs, but it may also affect the commercial brands.
If your water works admits to adding a lot of chemicals to your water, you
might want to try the bottled kind.
Hope one of these helps.