I like cool lye, room temperature oils and individual molds to make salt bars.
It helps to know that, while the initial temperature your oils and lye is important, for salt bars you need to keep an eye on anything that will cause the batch to heat up too quickly, or retain the heat, or add to the heat.
The extras:
Additional heat can come from:
Oven processing (most people here recommend against CPOPing salt bars for a good reason - the added heat can easily trigger a volcano)
Melting ingredients, such as butters (hint: melt these separately, and mix into the batch oils and let the whole lot get as cool as possible before you start)
The season (making salt bars in Summer can provide enough added heat to trigger overheating, even in individual molds).
Accelerating ingredients (anything that speeds up saponification will cause a rapid increase in heat)
Rapid mixing (which again will cause a rapid increase in heat due to the increased rate of saponification,).
Retaining heat
Larger mold sizes (I posted on the
effect of mold sizes here, but the basic premise is that thermal mass holds heat)
Insulation (this becomes dependant on your mold, batch temperature and ambient temperature; personally I don't insulate these soaps)
Mold materials (even something as simple as using a wooden mold can act as insulation for the batch, being aware of this is useful)
"Does effect the batter if it's too warm?"
Your batter can feel like it's "too warm" just before you pour it into the mold, however the very act of pouring it will cool the batter slightly.
If you are concerned that the batter is too warm, please know that you can do something about it (see below).
My most recent CP salt batch was made in a slab mold (retains heat), with a butter (melting fats added heat), honey (additive added heat) and beeswax (required melting).
As you can imagine, adding all of these ingredients and using a slab mold was a combination well outside of anything I would recommend you do (it did want to volcano), but it does bring us to an important point ... heat reduction!
Heat reduction (after you've poured your soap):
Remove from any source of heat (including the bench underneath soap! Moving the mold to a cool spot on the bench is sometimes enough)
Remove insulation (if you have used any, take it off)
Raise off a solid surface (I use a commercial cake rack to allow air flow under larger batches)
Air movement (anything that moves the hot air away from the soap helps; cover with fine netting to avoid dust if outside or near a window)
Water/ice bath (this is a method of last resort, but is extremely effective at stripping heat out of a batch - for wooden molds, place in a water-tight, open top bag first, and don't submerge past the top of the mold)
