How to freeze Sourdough Starter

Suppose you also recognize yourself in this scenario and must put your Sourdough Starter on hold. In that case, you can choose refrigerated storage, which is suitable for storing the Sourdough Starter for 1 to 4 weeks, or for a more extended period (1 to 12 months), the option of Freezing the Sourdough Starter and storing it in the freezer turns out to be the only viable way. This type of storage slows down the yeast’s vital functions and allows it to hibernate naturally while remaining alive. Nature has provided yeast with natural “cryo-protective” substances such as Trehalose that help the yeast cell live in such environmental conditions. So, have no fear; your yeast will survive!

Preparing the Sourdough for storage in the freezer is a relatively simple operation and consists of refreshing the starter after the bath with the following proportions:

1Kg (4 1/4 cup) of Sourdough starter

2Kg (8 1/2 cup) of 00 Flour (W 360)

800gr (3 1/3 cup) of water at 30°C (86°F)

Once the ingredients are mixed, roll the dough to a thickness of 1cm, fold it into 3, and soaked in fresh water (at 19-20°C, 66-68°F); try to respect a 1:3 ratio of starter vs. water (1kg of yeast soaked in 3l of water). Once it has come to the surface, place it in the refrigerator at +4°C (39°F) for 24h and then in the freezer (better blast chiller for those with one) until completely frozen. Once frozen, wrap the Sourdough with a sheet of food-grade cellophane and store it for as long as necessary.

How to activate the frozen Sourdough

Reactivating the frozen Sourdough Starter takes time and should be planned at least 10 to 15 days before you want to use the starter in your recipe. This longer recovery time is obviously due to the yeast’s unusual weakness during the storage period in the freezer.

Protect the Sourdough Starter from extreme temperature shocks (e.g., going directly from -18°C in the freezer to the room temperature of +20°C) to avoid severe damage to the yeast cell. On the other hand, once it comes out of the freezer, the Sourdough Starter will need to stay in the refrigerator for 24 hours at +4°C (39°F) and then for an additional 24 hours at room temperature.

After 48 hours (24h in the refrigerator + 24h at room temperature), bathe the Sourdough in water at 38°C (100°F), where you will have added 4gr/l of sugar (or even better, fructose) to purify and oxygenate the yeast. Since your starter will be extremely weak, you will notice that it will tend to rise to the surface almost immediately once immersed in the water. This is normal; continue the soaking for 18 to 20 minutes and wring out the pieces of Sourdough thoroughly before continuing with the next stage.

When the yeast is ready, refresh it first, bringing in nutrients and oxygen to strengthen it daily. The proportions for refreshments are the standard ones, namely:

1Kg (4 1/4 cup) of Sourdough starter

1Kg (4 1/4 cup) of 00 flour (W360)

300gr (1 1/4 cup) of water at 30°C (86°F)

When everything is kneaded and has reached a fairly firm consistency, roll out the dough to about 1cm thick to oxygenate it and stimulate the production of yeast cells. After that, fold it into 3, soak it in cold water (19-20°C, 66-68°F), and place it at room temperature until it reaches the surface. From that time, estimate an additional 24 hours to allow proper acidification. If after 24 hours after refreshment, the yeast will still be at the bottom of the bowl, do not be afraid; it is just a sign that the sourdough is extremely weak and needs additional time to re-establish the correct balance of yeast and bacteria within its ecosystem. For the same reason, it is essential to give the Sourdough the time it needs (which cannot be predicted in advance) to reactivate properly without proceeding with the following refreshments until the first one has been appropriately concluded.

For excellent sourdough reactivation, you should feed at least 700gr (3 cups) of the starter for the first few days (so as not to dilute the yeast too much) and gradually decrease the amount to your liking the following days.

As I mentioned, schedule 10 to 15 days before using a sourdough you have frozen for several months!

• Here is a brief recap for properly reactivating frozen sourdough starter
• Remove from the freezer and place it for 24 hours in the refrigerator at +4°C
• Place the starter at room temperature (20°C, 68°F) for 24 hours
• Bath your starter
• Refresh the starter with a Yeast: Flour ratio of 1:1
• Roll out and soak in cold tap water (19°C, 66°F), respecting a starter vs water ratio of 1:3 (1kg of Sourdough in 3l of water)
• Wait for the Sourdough to rise to the surface (this can take more than 24 hours)
• Once afloat, let it ferment for an additional 24 hours
• Proceed with daily refreshments for at least 10-15days

Conclusion

Compared to refrigerated storage, which allows you to store Sourdough for short periods (1 to 4 weeks), storing Sourdough in the freezer is a must if you want to keep it for periods ranging from 1 to 12 months. In addition, it is undoubtedly a convenient option to manage your starter at home, where it is occasionally used, and an excellent way to ensure a “safety stock” to make up for any eventual accidents.

As we have seen, the steps are not technically complex, but time is the secret to ensuring the best result and getting the sourdough back to the right strength before it is used in your recipes.