Why Freezing Your Sourdough Bread Makes It Even Better

FoodEducation
Written By Dr. Bill Schindler

A few weeks ago, we shared the exciting news that the Modern Stone Age Kitchen is now using 100% organic flour for all our gluten-containing products. This week, I want to take things a step further: explaining not only how sourdough transforms bread into a safer and more nourishing food, but how freezing it makes it even healthier.

Understanding Glycemic Index (GI)

Before we dive in, a quick note on glycemic index—or GI: it’s a measure of how quickly carbohydrate-containing foods raise your blood sugar.

Foods on the low end of the GI scale (55 or below) deliver energy steadily and support balanced blood sugar, while high-GI foods (70 and above) can trigger rapid spikes followed by crashes, leading to cravings, inflammation, and metabolic stress.

This context is important, because it’s exactly where sourdough—especially when frozen and toasted—shifts the needle in your favor.

The Power of Genuine Sourdough

Whole grains, straight from the field, are poorly suited to human digestion. Their nutrients are locked inside tough cell walls and bound up by natural compounds like phytic acid and lectins, which make minerals and proteins largely inaccessible to us. Without proper processing, our digestive systems cannot fully access or safely handle the nutrition grains contain.

But with sourdough, a partnership of wild bacteria and yeast:

  • Deactivates phytic acid, unlocking vital minerals.

  • Activates proteases, breaking gluten into more digestible amino acids.

  • Lowers dough pH, creating an inhospitable environment for pathogens while supporting beneficial microbes.

  • Consumes starches, as wild bacteria and yeasts feed on them, transforming them into acids and gases—and leaving behind fewer starches to spike blood sugar.

Sourdough doesn’t just give you bread—it creates a more deeply nourishing, flavorful food your body can actually use.

Dr. Bill shaping sourdough at the MSAK

A loaf of frozen rye in our freezer!

How Sourdough and Freezing Work Together

The sourdough process alone already transforms bread dramatically. Conventional white or whole-wheat bread typically scores around 71 on the glycemic index (GI)—squarely in the “high” category, comparable to eating candy. But when those same grains undergo a long, wild sourdough fermentation, the GI drops to about 54, placing it firmly in the “low” category alongside foods like yams and green peas. That’s a shift that turns bread from something that spikes blood sugar into something that fuels steadier energy and balance.

And then it gets even better. Once baked, sourdough bread can be frozen and reheated to lower the glycemic response even further. Freezing changes the structure of starches in the bread, turning a portion into resistant starch—a form that resists digestion in the small intestine and instead becomes food for the beneficial microbes in your gut.

Here’s what research shows:

  • Fresh bread produces the highest blood sugar response.

  • Freezing and defrosting lowers that response by about 30%.

  • Freezing and then toasting can reduce it even further, sometimes by as much as 40%.

Put together, this means sourdough bread that starts out with a low GI becomes even more blood-sugar friendly after freezing and reheating—delivering not just fewer spikes, but extra prebiotic benefits for your gut.

Best Practices for Freezing Sourdough

To get the most out of this:

  • Freeze soon after baking, ideally in slices so you can use just what you need.

  • Store airtight to preserve freshness.

  • Reheat before eating—toasting frozen sourdough doesn’t just restore the crust and crumb, it maximizes the resistant starch effect.

  • Three days of freezing is enough—longer storage doesn’t increase the effect.

  • Use genuine sourdough—commercial loaves with additives won’t yield the same advantage.


By the Numbers

For those who want to see the data, here are a few highlights:

  • Regular white bread: GI ~71 (high)

  • Genuine sourdough bread: GI ~54 (low)

  • Frozen and defrosted bread: ~30% lower glycemic response than fresh bread

  • Frozen and toasted bread: up to 40% lower glycemic response than fresh bread

  • In one trial, fresh bread yielded a blood sugar peak of 132 mg/dL, while frozen and reheated bread reduced that to 120 mg/dL.

Why This Matters

At Modern Stone Age Kitchen, our approach blends ancestral wisdom with modern science to help you eat better—without sacrificing flavor or convenience. Freezing sourdough isn’t a shortcut—it’s a carefully considered, science-backed step that enhances an already nourishing food.

So next time you pick up a loaf, remember: slice it, freeze it, and make every meal not just nourishing, but intentionally more healthful.


Further Reading:

Sourdough & Glycemic Index

Freezing, Toasting & Resistant Starch Benefits

Understanding Glycemic Index & Bread

Dr. Bill Schindler

Dr. Bill Schindler, author of Eat Like a Human, is an anthropologist, chef, and global leader in ancestral foodways. As the Founder of the Food Lab and Executive Chef at Modern Stone Age Kitchen, he transforms ancient techniques into modern practices for nourishing, sustainable eating. Bill’s research and teaching empower people to reconnect with traditional diets and improve health through fermentation, nose-to-tail eating, and other transformative methods.

https://modernstoneage.com
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