Can you turn all-purpose flour into self-rising flour?

YES! I am Queen of substituting ingredients. It is just baking powder. I can’t even get self rising flour where I live. There are several ways to do it.

From Wiki answers:
a simple method and although it is an estimate,
1½ teaspoon of baking powder and ¼ to ½ of a teaspoon of salt to every 1 cup of all-purpose flour.

Ingredients
Here are a few versions of making SR Flour:
• 500 gm. plain flour + 2½ tsp. baking powder + a pinch of salt
• 500 gm. plain flour + 20 ml. cream of tartar + 10 ml. bicarbonate of soda
• 1 cup plain flour + 1½ tsp. baking powder + ¼ tsp. salt
• 225 gm. plain flour + 2 level tsp. baking powder
• 450 gm. or 16 oz. plain flour + 1 oz./25 gm. baking powder
• 1 cup plain flour + 1¼ tsp. of baking powder.

Some cooks suggest a half teaspoon of baking powder per cup of flour as the easiest way.

• To make baking powder : Place 3 tsp. bicarbonate of soda and 4 tsp. cream of tartar in a jar and shake them well together. Store in a cool place.

Just a note to add to @cazzie ‘s excellent answer:

The ingredients added to flour to make it “self-rising” behave a little differently than the baking soda/tartaric acid combination will in terms of when they release their CO2. Baking soda/tartaric acid produces CO2 as soon as moisture enters the mix. Commercial self-rising flour produces Co2 under the influence of heat.

This makes a difference in a couple of ways. First, the homemade version can’t be stored for long. Humidity will eventually rob the flour of its leavening potential. Second, because the homemade begins foaming when moisture is added, some of that CO2 will be lost as further mixing collapses the foam structure of the dough/batter. The commercial version will wait to react until the dough/batter is in the oven and not being manhandled anymore. Less CO2 is lost.

The best substitutions are the ones using double-acting baking powder rather than baking soda/tartaric acid. This has both a moisture-triggered component and a heat-triggered component.

(Doesn’t everyone know that if you use baking soda, you can’t stir it endlessly, but just a quick mix and pop it in the oven?) If, not, then, yes as @thorninmud points out. If you use baking soda in ANYTHING, do not over mix. That is basic baking knowledge.

But what I wrote was to add cream of tarter to it. Baking soda + cream of tarter = baking powder. Organic chemistry lesson:

Adding acid salt (cream of tartar and/or sodium aluminum sulfate) to Sodium bicarbonate (backing soda) creates a weaker, but two stage reaction and a more stable reaction. The batter can sit on the counter now 15–20 minutes before baking.

Why use baking soda at all if it is so much more touchy than baking powder? The ‘umph’ of baking soda is needed for formulas… (oops) recipes with an acidic ingredient, like: vinegar, citrus juice, sour cream, yogurt, buttermilk, chocolate, cocoa (not Dutch-processed), honey, molasses, brown sugar, fruits and maple syrup.

You know why ‘Devil’s Food Cake’ got it’s name? Back in the day, when making chocolate cake with baking soda, because of the chemical reaction between the cocoa and the baking soda, it turned the cocoa a tinge of red, giving the cake a ‘reddish brown’ colour and they didn’t have the chemistry knowledge to know what was going on… so ‘Devils Food’ was legend. (some people say it was the use of beets in the recipe, but I can’t really find any stories of beets being used that go back further than the baking soda sources, so I think the beets came after.) ANY acids in cake turn the cocoa a reddish colour. Red Velvet cake originated from this as well.

When baking a cake, don’t skip the step of sifting the flour. This step really helps the levening agent (the baking powder or baking soda) create nice uniform airiness. Even if you are baking from a ready made mix, sift it before adding the wet ingredients and you will see a very pleasing difference.

Hope this helps. I love baking and this type of food chemistry. (does it show?)

Baking soda + cream of tarter (which is a weak form of tartaric acid) = single acting baking powder.

Double acting baking powder doesn’t use cream of tarter as the acid mostly because most people are not very good at not over-mixing. Instead, they use a combination of sodium aluminum sulfate and calcium phosphate as the acidifiers. Calcium phosphate behaves a little like cream of tarter, but it reacts more slowly; sodium aluminum phosphate really doesn’t become avilable for reaction until the mixture is heated.

All of this delay business is really about buying extra time for people to mess with the batter/dough without paying a penalty in leavening power.

The baking soda/cream of tarter works better than just the baking soda alone.

We’re trying to help the OP find substitutes that they can find at the grocery store or they already have in the pantry. If they don’t have baking powder, baking soda and cream of tarter works pretty good. I don’t even have sodium aluminium sulfate or calcium phosphate in my mad lab downstairs.

Actually, they don’t add aluminium sulfate to baking powder here in Europe any more. It is used as a preservative for some products containing eggs and it is used in candied fruit, from what I can gather, but there was some issue about putting aluminium salts in food. Most all calcium phosphates are not allowed in our food, so which E number were you referring to? E540, 542 543 and 544 and not allowed in our food.

On the back of my baking powder box is dinatriumdifosfat (E450i) and hydrogenkarbonat (E500). So…. there you go. I like simple answers.

Right, and I was just saying that if the OP had the choice he’d be better off using the double acting baking powder instead of the soda/cream of tarter combo.

I would argue that those are unnecessary chemicals to be cooking with.

OK, but if the OP’s interest is in duplicating the action of self-rising flour (which does have those chemicals) then…

Thank you, @thorninmud and @cazzie, for your responses! Good to know that I don’t even have to keep baking powder around, either. Thank you for that information. I usually end up throwing out my can of baking powder by the expiration date, and it’s still mostly full! Now I know that I can sorta re-create baking powder by using cream of tartar + baking soda.

Baking powder has an expiration date? :O

Baking powder and baking soda can both lose their effectiveness over time, especially if not kept in an airtight container.

Yes, baking powder has an expiration date. It’s marked on the can. I understand that the acid and the base in it eventually neutralize each other, and it loses its effectiveness because it can no longer create bubbles.