Why does chickpea flour need to rest for several hours?

Question

Many traditional Italian recipes make use of chickpea flour (e.g. farinata and cecina). Before cooking the recipes suggest to mix the flour with water and make it rest for several hours (in some recipes they suggest 6/7 hours).

What happens from a chemical point of view? Does such a long time really makes a difference?

Answer 1

Chickpeas are high in phytic acid.

• This is good, because it's a nutritional anti-oxidant, helps prevent kidney stones, and has other health benefits.
• But it can be bad because humans don't produce phytase, the enzyme that digests phytic acid, which will bind to other nutrients, such as iron, zinc, and calcium, making them nutritionally unavailable.

Long slow cooking, or long soaking will break down most of the phitic acid, leaving enough for the benefits while removing most of the detriments.

A closer look at phytic acid Phytic acid, or phytates, is the stored form of phosphorus found in seeds, nuts, legumes, and unprocessed whole grains (concentrated in the outer bran layers). The amount of phytic acid in these foods varies widely even within the same food, based on the seed type, environmental conditions, climate, and soil quality. Phytic acid can have health benefits due to its antioxidant properties. Laboratory and animal studies show that it can protect against DNA damage and cancer cell growth. The chemical name for phytic acid, inositol hexakisphosphate or IP6, is very actively studied in cancer research and, though research is still early, IP6 has become a popular over-the-counter supplement. Phytic acid can also prevent kidney stones from forming by inhibiting the buildup of calcium crystals, a component of kidney stones.

However, phytic acid is also labeled an antinutrient because humans lack the phytase enzyme needed to break it down. As it passes through the gut, phytic acid binds to minerals like iron, zinc, and calcium so they are not well-absorbed in the intestine. This will occur only when phytic acid is eaten with foods containing these minerals at the same meal. The average Western diet usually has enough nutrients and variety to protect from a true deficiency, especially with the inclusion of some animal proteins (e.g., lean pork, poultry, shellfish) that are rich in zinc and heme-iron, a well-absorbed form of iron. A nutrient deficiency more likely occurs in developing countries where a variety of food choices is limited, the risk of malnutrition is higher, and legumes or whole grains are staples that are eaten with every meal. Also at risk are those who eat a vegan diet (which not only consists of plenty of seeds/nuts, legumes, and grains but these foods contain poorly absorbed non-heme iron), or those who already have an iron or zinc deficiency due to medical reasons.

How you prepare foods high in phytic acid can reduce the overall amount. Cooking, soaking overnight in water, sprouting (germination), fermentation, and pickling can all break down phytic acid so that the phosphorus can be released and absorbed by the body. Some natural bacteria in the colon contain the enzyme phytase and can also help to break it down.

— Are anti-nutrients harmful? | The Nutrition Source | Harvard T.H. Chan School of Public Health

Answer 2

As chick pea is not a chemical, it is hard to say. 2 options come to my mind:

1. It is possible the hydration at natural pace at room temperature provides better results. Direct boiling and related protein denaturation may affect the hydration.
2. Legume frequently contains insoluble polysacharides like inulin(an analog of starch, based on fructose), which are not digestible by humans, but as consumed by bowel bacteria, causing flatulance. Long term soaking probably activates Inulinase, what is an enzyme hydrolyzing inulin to fructose.
3. About phytic acid (inositol hexakisphosphate), read the Rays answer. Note that according to its chemical structure, it does not seem to have antioxidant properties.