>Roy thanks for your answer! It was very helpful. Would it be a correct
>assumption that active dry yeast need a "tepid" start with some of the
l>iquid,flour and perhaps a bit of sugar to activate it, whereas
instant
>doesn't (it's activated more readily)? The pack here desn't really explain
>anything or give instructions, so it just leaves you wondering... And how do

I had done many variations of the hydration procedures by the yeast
manufacturers. Some yeast are robust enough that it does not show any
difference whether you hydrate it with tepid water or just tap water at
25 degeee C, but others are sensitive to such. If I have not used a
certain yeast brand that I the way I do ,hydrate in tepid water.
It is not necessary to add sugar, but I add flour along with the yeast,
maybe one part yeast to 1-2 parts flour; but I have done many times
without doing so and the results is virtually the same.. The flour is
just an insurance that the yeast has a suitable substrate to
'chew' upon cell release on hydration.
Pre-activation is recommended for active dry yeast as the granules are
coarser and if you add it directly to the flour like instant yeast, you
will end up with undissolved granules of active dry yeast affecting the
dough fermentative activity .
.. Beside most active dry yeasts are dried differently from instant
yeast and that can also contribute a considerable percentage of dead
cells in the active dry than in the instant version.
If you just soak it in normal tap water, there will be an increase of
dead yeast cells due to cold shock where the cell membrane will rupture
leaching out its cellular components; hence will result in weakening
the dough resulting in less volume, flatter symmetry , some yeasty
taste.
The instant yeast could also have that cold shock effect therefore its
recommended that its be blended with flour so that during hydration the
flour particles will form a barrier between the yeast shielding them
from the shock.
The most preferred way of hydrating instant yeast is to follow the same
procedure as the instant yeast and there will be very minimal yeast
cell degradation resulting that your dough will rise optimally.
Therefore if you plan to use only 2/3 of the active dry yeast quantity
and get the same result as the full amount dry yeast, do the hydration
in tepid water.
In recent years the drying process of the active dry was done much
better and there is less residual dead yeast cells and the particles
size in some brands are almost the same as the instant yeast and you
can just add it directly to the flour as well.
In addition genetic modification of the yeast resulted in much improved
yeast performance that some are already on par with instant yeast in
activity.

>you use yeast quantity-wise in really hot weather? Thanks for your time!

In hot weather the bakers reduce the yeast to compensate for faster
fermentation rate at that elevated room temperature.
That is why you had to reduce it by a certain percentage in order to
get the same of a controlled fermentation and proofing rate.
But being too academic in your breadmaking sometimes make your prone
to mistakes; If I am just making bread at home and I don't need to
follow the hydration details and measurements to the letter and just
take it easy most of the time.
I am only strict with details if I am at work.
Roy