by Jennifer Beazer, MPH, RD, LDN — Registered Dietitian
Estimating the protein content of the yeast in a sourdough starter is challenging. Traditional bread, like Brenda’s Sandwich Bread, contains commercial yeast as an ingredient in the starter (the yeasty mixture that gives the bread rise and texture). In contrast, sourdough bread starter has two ingredients at the outset: flour and water. The starter then grows what is called naturally-occurring yeast through a process of “feeding” (adding flour and water) and “discarding” (removing mass) from the starter.
As both a dietitian and scientist, I began by reviewing the existing research. I found limited data on the protein content of naturally occurring yeast. This meant that Cook for Love had to make an estimate of protein and phe based on the best-available data. We consulted dietitians and experts in food science and metabolism. Together, the Cook for Love Nutrition and Food Science Committee worked to determine the upper estimate for protein content in a sourdough starter.
Definitions:
- Commercial yeast refers to packaged baker’s yeast (like active dry or instant yeast), which has a known and consistent nutritional profile.
- Naturally-occurring yeast develops over time through fermentation in a sourdough starter, cultivated from flour and water exposed to ambient air and microbial activity.
While the phenylalanine (phe) content of naturally-occurring yeast is expected to be similar to that of commercial yeast (on a mg phe/g basis), its actual contribution to a starter’s protein content can vary due to several factors, including:
- The age and activity of the starter
- Temperature and humidity during fermentation
- Frequency and method of feeding and discarding
- The type of flour used
- Overall microbial composition and pH of the starter
Because of these variables, our Nutrition Validation Committee would like to share the following assumptions that informed the estimate of the pro/phe content of the starter used in the Cook for Love Sourdough Bread recipe.
- The phenylalanine content of naturally-occurring yeast is assumed to be similar to that of commercial yeast.
- The maximum estimated amount of naturally-occurring yeast present in the starter is 20g. This is based on the difference in starter weight over time, accounting for regular feeding and culling.
- At most, 60g of un-metabolized flour remains in the 140g of starter at the time of recipe use.
The value for the protein & phe in the starter used in the Sourdough recipe represents the committee’s best estimate; each starter will be unique and may vary somewhat from these estimates. As with any new food in your diet, checking your blood levels can help you determine how that food best fits your diet.
Making your own starter
If you cannot get an established starter, this is how you would go about making one.
- Day one: Take a glass mason jar. Add 100 gm of flour and 100 gm of warm water. Stir well. To gauge the amount of rise, place a rubber band around the jar at the height of the mixture. Cover and store in a warm place (80 degrees ideal).
- Day two: Discard the content of your jar to 75 gm. Add 100 gm flour and 100 gm warm water. Mix well. Cover and store in a warm spot for 24 hours.
- Day three: Discard the content of your jar to 75 gm. Add 100 gm flour and 100 gm warm water. Mix well. Cover and store in a warm spot for 24 hours.
- Day four: At this point you should start to see some fermentation bubbles scattered on top. Now you will refresh your starter twice a day. Discard to 75 gm, add 100 gm flour and 100 gm warm water, mix, cover, and store in a warm spot for 12 hours. After 12 hours repeat again. Let it rest overnight.
- Days five and six: Repeat the same instructions as day four. Fermentation activity should increase more and more.
- Day seven (and onward): In the morning, discard the contents of the jar down to 20 gm. Add 100 gm of flour and 100 gm warm water. Cover and store for 12 hours. In the evening, repeat and let rest overnight.
If you are not making bread every day (which I do not), simply store your starter in the fridge. Take 20 gm ripe starter with 100 gm flour. Add 80 gm room-temperature water and mix. Cover and let sit on the counter for one to two hours, then place in the fridge for a week. To revive, let the starter sit on the counter for two hours to warm up. Stir, then begin the normal feeding cycle again (discard to 20 gm, add 100 gm flour, 100 gm water). Place the jar in a warm spot and let it sit for 12 hours.