Why do some powders clump in hot water?

Question

Why do some powders like flour or green tea causes lumps in hot water while other powders like sugar or cocoa readily dissolve?

Asked by Chloe

Answer

Water is a great solvent for polar molecules. Sugar, table salt, and other small polar molecules are water soluble. When you put them into water, you get a sugar resp. salt solution.

Other molecules are not soluble in water. Most organic molecules with a carbohydrate tail are insoluble (unless they have a strongly polar active group, like the shorter alcohols). Starch and cellulose are not water soluble. Most plant matter is made mainly from starch and cellulose. (The exception are fruits, which can have more fructose than starch, but still lots of cellulose).

When you put non-soluble powder into water, you are not making a solution. You are making a colloid known as sol (solids dispersed in a liquid). If you wet salt, the water will dissolve the first layer, and the second layer will be exposed. If you wet a random non-soluble powder, the water will have to wash away the first layer before it reaches the second layer, so it is hard to make the suspension without vigorous stirring.

There are some special molecules which absorb water and swell. Starch, some proteins (gelatin) and some polysaccharides (xanthan gum) are common such molecules in the kitchen. When you wet them, the water gets absorbed by the first layer. This changes the viscosity of the layer, making it thick and clingy. This forms a clump. In the core are the dry layers of powder. They are held together by a bubble of the water-swelled substance. Outside of this bubble is the water. It can't wash away the bubble, because it is so viscous, it doesn't flow into the water. And the bubble protects the core of the clump from contact with water. This happens with starchy powders like flour, or also real cocoa powder. Tea powder is mostly dried cellulose, so it is also hard to dissolve.

You mention cocoa as easily solved in water. In fact, cocoa is very hard to dissolve, so I think you are speaking of a cocoa flavored drink. A cocoa flavored drink is a mixture of dextrose, cocoa powder, and other things (but mostly dextrose). In such a mixed powder, the water dissolves the soluble molecules (the dextrose), and the insoluble particles (the cocoa powder) which were suspended in the dextrose are now suspended in the water. No neighbouring cocoa particles to cling to. So, no clumps, but an instantly homogenous drink.

Answered by rumtscho

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alternative leavening agents other than baking powder, and their ratios of substitution

Question

Please provide a list of alternative ingredients to baking powder, and how much of the substitute to use in place of baking powder.

Answer

I must confess, I can't give you straight substitution amounts -- all of these leavening agents behave somewhat differently, so in most cases a straight substitution for baking soda isn't appropriate.

Ye Olde List of Leavening Agents:

Biological Cultures (Wikipedia, plus kefir whey I've seen recipes for)

• Yeast - norm is 1 tsp/pound flour for 1-2 hour rise time
• Sourdough - uses 1/2 to 1/4 of final flour mass, rise time varies
• Kefir whey - similar to sourdough, unknown rise time or measurement
• Buttermilk - no clue what substitution ratio, but wikipedia lists it. Probably acts similar to kefir whey and sourdough.
• Yogurt -- wikipedia lists this as a leavening agent too, but I'm skeptical.
• Beer (unpasteurized, with live yeasts)
• Ginger beer (same deal)

All of these share the common ability to ferment flour, when handled properly.

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Chemical Leaveners (Pulled straight from On Food and Cooking)

• Pearlash and potash (mostly potassium carbonate). Purely historical leaveners, these were derived from wood ashes, and were the predecessors to baking soda.
• Hartshorn AKA baker's ammonia (mix of ammonium carbamate and ammonium carbonate). Not used much anymore. It was once made from deer antlers, ergo the name. When heated, this produces both ammonia and carbon dioxide. Because of the ammonia, this cannot be used as a straight substitute for baking powder, due to the changes in flavor and smell it causes.
• Sodium bicarbonate (baking soda), basic component of baking powder, reacts immediately with acid
• Cream of tartar (tartaric acid) -- Acidic component, reacts with bases immediately
• Monocalcium phosphate -- Acidic component, common in baking soda, reacts immediately
• Sodium aluminum pyrophosphate -- Acidic component, reacts slowly with base after mixing
• Sodium aluminum sulfate -- Acidic component, provides the "double" in most double-acting baking powders. Reacts slowly under heat.
• Sodium aluminum phosphate -- Acidic component of double-acting baking powder, acts during early cooking at 100-104F/38-40C
• Dimagnesium phosphate -- Acidic component of double-acting baking powder, reacts early in baking @ 104-111F/40-44C
• Dicalcium phosphate dihydrate -- Acidic component of double-acting baking powder, reacts late in baking @ 135-140F/57-60C

So, basically you need an acid + baking soda, or one of the heat-activated compounds (hartshorn, or one of the last four salts). In many cases a dough can provide its own lactic acid.

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