Predicting OG in Beersmith

[Tricky Dicky]

I'm a partial BIAB brewer with limited experience and wanted to know the best way to estimate OG for a recipe. I use Beersmith to create and verify recipes and have noticed that speciality malts are contributing to the estimated OG. My understanding is that speciality malts don't have much in the way of fermentables to offer so why do they increase the estimated OG (in Beersmith) when added to a recipe? Should I zero out their Potential OG when including them ?

 

[W.stephaner]

Deleted as talking bollox

 

[MHB]

Mostly wrong - sorry but learn before posting, if you don't know ask....
O.G. is short for Original Gravity, it is a simple statement that the something has an apparent density X times that of water. If I said the OG was 1.050, 1L of that wort would mass 1.050 times as much as 1L of water or 1.050kg/L.
That's all it is saying, nothing about fermentability.

Any malt toasted/kilned past about 20-25 EBC will have all the enzymes in it denatured (killed), so it wont contribute to the ability of the malt to convert starch into soluble sugars (among other processes).
A definition of a base malt is a malt that has enough enzymic power to convert itself (most have way more) Dark Munich is about the cut off at ~20EBC its barely able to convert itself.

The colour in malt comes mainly from Milliard Reactions, these are heat caused joining of proteins and sugars, Milliard products are generally pretty un-fermentable but remain soluble, so they contribute to the OG, and will remain in the beer contributing to the FG.
When we start lookin at really dark roast malts a lot of the colour comes from burned starch just like burnt toast, even burnt coffee beans, go too far and it tastes pretty bad but a bit of toasting add interesting flavours.
As a rule the darker you toast the malt (or barley), the less soluble material there will be (down from say 80% before roasting to 65% after). The amount of the potential extract that is fermentable will also go down, by the time you get to Roast Barley/Black Malt (say over 1,000EBC) the extract will be pretty much totally un-fermentable (food colouring),

Anything soluble will add to the OG, the part of that, that is fermentable will get consumed by the yeast and so we get a lower FG.
If I added some Lactose, it would add to both the OG and the FG as it is soluble but unfermentable.
The same amount of Sucrose would add the same to the OG, but as its fully fermentable it wouldn't be part of the FG (the alcohol made from it would).

I imagine a partial BIAB brewer is a minimasher who uses extract/sugars and a very small BIAB mash to make up extra flavour.
Mark