Understanding Phytic Acid in Sourdough and Whole Grains

Phytic acid in sourdough and whole grains

I’ve been getting some questions about the phytic acid in whole grains and sourdough, and thought it would be a good idea to go into detail about how this works, and why you don’t need to be alarmed about it.

Along with a bunch of good stuff that is not in refined flours, phytic acid is present in whole grains. If phytic acid is not broken down by the phytase enzyme by soaking, sprouting, or fermenting, it can bind to the iron, zinc, magnesium, and calcium in the grain, making it so these nutrients in the grain are not absorbed by your body when you eat the grain.

During sourdough fermentation, the enzyme phytase is activated. Phytase breaks down phytic acid. As sourdough ferments and gets more acidic, phytase is more active. Phytase converts phytic acid into phosphorus, making it beneficial for bone health.

Phytic acid also has anti-inflammatory properties, and helps to stabilise blood sugar.

A longer sourdough fermentation will reduce the phytic acid by up to 90%, compared to less than 30% for yeast breads, and less than 50% for soaking whole grains. Sprouting will reduce phytic acid in similar amounts to sourdough fermentation.

In A Year in an Off-Grid Kitchen I wrote about my approach to this issue: if you are relying on a lot of grains and not eating much in the way of mineral-rich foods such as bone broth, red meat, and dairy, it’s probably best to always soak, sprout, or ferment your grains and legumes. If you are eating plenty of nutrient-dense animal foods, then you can get away with baking unsoaked whole grain cookies, muffins, and other treats every now and then.

I have not bought flour for over seven years, I also don’t have the setup to reliably dehydrate sprouted grains, so if we want to make a favourite recipe that isn’t soaked or fermented, we just make it from the fresh milled flour that we mill ourselves, enjoy it, and that is that.

For our bread, which we eat every day, we make 100% whole grain sourdough.

How to reduce phytic acid as much as possible:

• Slow down your fermentation. Reduce the temperature or the amount of starter in a recipe, to make fermentation take longer.

• Cold proofing (also called retarding) is probably the most reliable way to reduce phytic acid, because the phytase enzyme is more active in the acidic environment of fermented dough. To cold proof, simply follow your recipe up until it’s time to proof the dough, then move it to a place below 8ºC (46ºF) for up to 24 hours. Make sure to cover it with something airtight if you’re proofing it in a fridge.

• You can also retard the dough during bulk fermentation. This may not be quite as effective as cold proofing, but it will still make a big difference, and can be a great way to make bread if you want to mix the dough at night and then have dough that’s ready to bake any time the next day.

• Using larger amounts of sourdough pre-ferment will start the dough off more acidic, so although the bulk fermentation time is faster than it is for a loaf with only a tiny amount of starter, the increased acidity at the start of fermentation means that phytase is more active from the very start.

• Add some rye flour. Rye is high in phytase.

• Just bake sourdough! I use pre-ferments, cold proofing, and cold fermentation at different times of the year, in order to make recipe timings that work with my schedule in seasonal conditions.

Why not just eat white flour instead?

The phytic acid in the whole grains is binding to the minerals in the whole grains. These minerals aren’t present in white flour, so you’re not getting any nutritional benefit by using white flour instead of whole grains.

Whole grains can be stored for many years, whereas flour of any sort will not keep long. If you want to grow your own grains in the future, the grains are not going to transform into white flour on their own, so it’s good to get used to baking with 100% whole grain flours now.

Free whole grain sourdough discard cookbook

Reduce phytic acid in whole grains the easy way with this free cookbook of fermented flour recipes