The best source I've found online is Joy of Baking. This article gives you a good idea of the percentage of protein you need to have in your flour to get the desired results in specific recipes. It's a site primarily made for Americans, which means that they give you volume measurement equivalents to grams. The site basically gives you all the information you need to calculate how to blend flours yourself, should the country you are currently living in not have certain kinds of flours, e.g. AP Flour (All Purpose Flour).
I thought I'd write a post about this as people travel a lot these days. If you're a single working expatriate you may not cook, but if you are moving around with a family the person staying at home might be doing some baking.
I've heard time and again about how 'the recipe doesn't work with the local flour', but haven't you noticed that no matter where you are, there is that lady or man who doesn't seem to be having problems with baking and is churning out all these amazing things? Why doesn't my cake rise? Why does her cake rise? What is wrong with my cake? There is usually a good scientific explanation as to why one person failed and the other did not. There is no need to engage in any superstitious rituals and there is no need to import flour from your home country.
According to Joy of Baking:
All Purpose Flour: 10-12% protein content
Cake Flour: 6-8% protein content
Pastry Flour: 8-10% protein content
Bread Flour: 12-14% protein content
Now, the country you're in may not have flour categorized in this manner. In Japan for example you will be able to find 2 types of flour: Hakuriki and Kyoryoku. Although Hakuriki flour is generally known as 'cake flour' and Kyoryoku flour is known as 'bread flour' I sent an email to Nissin asking them about protein percentages. They gave me their numbers for their most popular brand 'Camelia':
Hakuriki Flour: 8%
Kyoroku Flour: 12%
Remember basic algebra?
You know that this is what you have and now you need to figure out in what proportions you should blend these two bags of flour to get the desired results.
All Purpose Flour: 10-12% protein content
We'll take the median or the average, which is 11%, even though if you wanted a high percentage AP Flour you could presumably use Camelia Kyoryoku Flour as it's within the range of AP Flour. I have found from past experience that since the Kyoryoku Flour was formulated not for making bread, but for making 'Udon', it's easier to handle when you mix in some Hakuriki Flour which was formulated for making cake and French style butter cookies.
Let X=1 *Let 1 portion of flour=100g
This means that you should mix 100g of Hakuriki flour with 116g of Kyoryoku flour to get a flour with an 11% protein content.
For a 10% AP Flour in Japan:
This means you should mix 100g of Hakuriki Flour with 100g of Kyoroku Flour to get a 10% AP Flour. This is the formula I use and so far I've had good results with this. However, I know that should I want more texture, I could increase the proportion of Kyoryoku to Hakuriki.
If you need a 12% AP flour, just use Kyoryoku Flour, although I've found that since it is formulated for making 'udon' it can benefit from a little 'cake flour' blended into it.
To get the desired results, I've found that blending these flours at a 1:1 ratio (10% protein content) works well for me.
As for pastry flour, the 10% blend can work, but if you feel you'd like the crust to be a little more delicate, you need to blend slightly more Hakuriki flour in proportion to the Kyoryoku flour.
Pastry Flour: 8-10% protein content.
For a 9% Pastry Flour
This means that you should blend 100g of Hakuriki flour with 83g of Kyryoku flour.
For an 8% Pastry Flour, just use Hakuriki flour.
I have however found that the 9% blend gives the desired results.
Remember that each manufacturer in each country has formulated their flour to meet the demands of their consumers and you are a minority as a foreigner. If you find Japanese cakes to be too soft, well, unfortunately, this is the way the Japanese like their cakes to be. But this doesn't mean that you have to suffer eating these cakes. Just blend your flours a bit, using the formulas I've provided you with, and you'll get a cake that's more to your liking.
If you want to take this one step further, write your manufacturer back home and ask them for the exact percentages of protein they have in that specific brand of flour you used. I've already done that bit for you on the Japanese end so you can recalculate everything to make sure your blended flour will have the exact same percentage as the flour you were using back home.
If you don't live in Japan, you'll have to do the homework on both ends, but I think I've provided you with enough of a basic guideline so that you can manage to calculate the right proportions no matter where you are in the world.
Note 1: I've found that when I'm in Spain and I blend their regular flour (AP Flour) with their Cake Flour to make Pastry Flour, I need more water for the dough to come together. I am however not sure whether this is due to the protein content or whether their Cake Flour absorbs more water.
Note 2: The most common flour in Germany is Cake Flour. This could be due to the fact that in the past few decades (at least), the Germans bought their bread whereas they baked cake in industrial quantities at home. This means that a lot of foreigners who thought their most common flour was AP flour didn't have enough protein in their flour and ended-up baking different types of things with what's known as Cake Flour in America.
Note 3: When blending your own flour, it's easier to calculate ratios in grams rather than by volume. Doing this by volume means using a more complicated mathematical equation and I'm just not that good at math!