I'm getting tired of repeating myself on "Pretzel-Related" threads where discussion of "Lye" is concerned and I always have to resist the temptation to turn the whole discussion into a Chemistry lecture. I decided a few days ago to do a little "Kitchen Science" and do an incomplete, but slightly more detailed explanation of what alkalis are all about
What I wanted to do was examine some of the claims I've read here, and on many other pretzel-making/baking/soap-making sites. I got tired of reading YahooAnswers, where someone says "If you can't get Sodium Carbonate (Na2CO3), use Sodium BI-Carbonate, because they are very similar chemicals..." This is a true, but totally vapid and rather stupid statement. Common Salt, Sodium Chloride, (NaCL) is also a 'similar chemical' to Sodium BI-Carbonate, (NaHCO3) and similar to Caustic Soda, (NaOH) because they all have only one sodium ion, per molecule, when in solution...It doesn't mean they will perform similar chemical reactions on your bread or noodle dough, however
Understanding pH in detail isn't that straightforward or easy, but as a guide-line, pH7.0 is completely 'neutral' (or in balance) and it's the measurement you should get from pure distilled water. Lower numbers are found with sour, acidic foods, such as lemon juice and vinegar, around pH3-4. Numbers above 7.0 indicate a 'basic' or 'alkaline' property. Any liquid you test will be either acidic, [low pH, well-under pH7.0]; neutral [pH7.0 or pretty close to it]; or alkaline [pH higher than 7.0]
The problems arise when people fail to realize that the pH scale is "logarithmic" [or negative logarithmic] in the same way that dB [deciBels] are in electronics. This is an "engineering solution" to dealing with ridiculously big numbers. What this means is that the difference between one point on the pH scale represents a difference of a power of ten: pH8.0 is about TEN TIMES more alkaline than pH 7.0; a solution of pH9.0 is 100 times more alkaline; pH10 is 1000 times more alkaline, and so on...A tap-water reading in many cities around the world could be as high as pH8.5, which is also the most-often quoted pH figure for Baking Soda. Caustic Soda, or 'Pretzel Lye', on the other hand (one of the strongest known alkalis), is at least 5pH points higher, meaning that it is at least 100,000 times stronger than baking soda. It is this which allows the alkali to attack the surface starch of your pretzel dough quickly and that gives the brown color and the perfect crust that many pretzel fanatics love!
What I did was make solutions using 'Aqua Purificata', the nearest thing you'll find to pure, ion-free, distilled water at a reasonable price. I measured 3g each, using my most accurate scale, of Baking Soda, Kansui Powder (the ingredients of Chinese Lye Water) and Caustic Soda (or 'Pretzel lye') and mixed the powders with 100g of purified water. I mixed each solution for two minutes in brand-new plastic containers, rinsed with the pure water and dried with heavy paper towels. I measured the pH using an $80 pH meter that is fairly well-calibrated. After 3 minutes in each solution, I took photos of the meter readings. I now think I should have delayed the photography until 5 minutes had passed, but the pics I have will give you an idea of the differences among the three main chemicals I tested
I hope this is clear enough and useful to somebody,