Flours and the great all-purpose deception

A while back, I wrote about how to make your own self-rising flour, and it got me thinking of an old baker's rule of thumb for mixing cake and bread flours to substitute for all-purpose.  In a few of the professional kitchens I've worked in, this is actually a common calculation because the pastry department often has every flour but all purpose, as it seldom needs it, or has already standardized the calculation in the recipe itself, but on the savory side of the kitchen, someone is always coming in with a new recipe calling for all-purpose,  runs over to the pastry shop, only to be disappointed, then scrambles to figure out a substitution.  "60/40" is the ratio they are usually told, but before talking about it here, I thought I would be wise to double check, as rules of thumbs are not always correct.  Surprisingly, even finding reference to the 60/40 ratio on the internet was next to impossible - could it be that this old pastry rule of thumb is wrong?  Partly yes and partly no.  In fact, everybody's wrong, the whole stinking flour industry is wrong and all-purpose flour should never have been invented because it's impossible to standardize.  In truth, you can't even be sure about substituting all-purpose flour for all-purpose flour!  Here's why.

Generally speaking, different flours are used based on the relative protein content, which in turn will affect how much gluten develops as a recipe comes together.  Bread flour is hard flour and has lots of protein (12%-15%), cake flour is soft flour and has less (7%-9.5%).  Pastry flour is a blend closer to cake (7.5%-10%).  All-purpose is a blend as well, closer to bread and intended for general home use.  The problem is that somewhere along the line some knucklehead wanted to be different and depending on where you live, all-purpose can run below 10% or as high as 13% basically the full range from cake and pastry to bread.  Not exactly encouraging if you want consistent results.  But there's hope.  Generally, in North America terms, the Southern and Eastern regions will have the softer flour while the Northern and Western regions will have harder flour.  Supposedly this is because there's more biscuits and quickbreads made in the South and more yeastbreads in the North.  If you check the packaging on your flour, it should tell you the relative protein content for your region and you'll know if you fall into the harder or softer category.  Next you need to consider what you are making - is it a yeast or quickbread, chewy or tender?  Next, consider if you know the regional origin of the recipe - If you live in the North, and are making a recipe using all-purpose from the South, you may want to opt for a cake or pastry flour, and vise-versa.

So will the 60/40 ratio work?  and is it bread to cake or cake to bread?  yes - to both.  Depending on the strength of your bread and cake flours, the ratio can work either way.  Many cooks simply run it an even 50/50.  The important thing is to slightly soften your bread flour, more if it happens to be a strong one or the recipe using all-purpose is of a more delicate nature.  Being a stickler for details, I'll leave you with a few tools to math it out (using the metric system).  Obviously, it's easier to just have the right flour on hand, but sometimes you are just stuck and need to make things work.

 Flour                        weight                         protein per 100g       

bread flour              1 US cup = 127g                 12g - 15g
all-purpose flour     1 US cup = 125g                9.5g - 13g
pastry flour             1 US cup = 113g                7.5g - 10g
cake flour               1 US cup = 100g                   7g - 9.5g

 - if you know the strength of the all-purpose flour you need, then you know how much protein you want per 100g
 - check the protein level of your bread flour
 - check the protein level of your cake flour
 - play with the ratios  - example:  60g bread flour at 14% =  8.4g protein (60 x 0.14)
                                                    + 40g cake flour at 8%   =   3.2g protein (40 x 0.08)
                                                      100g AP flour at 11.6% - 11.6g protein

 - using the same math skills, you could also improvise your own pastry flour - I've even used them to calculate homo milk from 1% and half and half cream (I was in a spot, that's what I had and it worked)