Based on baking science and traditional rye bread techniques, the "boiled sour" listed on the label is almost certainly a descriptive term for a specific type of scalded sourdough starter, known in German baking as Brühsauer.
It is not a chemical additive, but rather a natural pre-ferment created by a specific process.
What is "Boiled Sour" (Brühsauer)?
In traditional rye baking, "boiled sour" refers to a method where a portion of the rye flour is "scalded" (mixed with boiling water) before being allowed to ferment with sourdough culture.
The Process: The baker pours boiling water over rye flour. This creates a hot, porridge-like paste.
The Fermentation: Once this "scald" cools down to a safe temperature, the sourdough culture (wild yeast and bacteria) is added to it.
The Result: The mixture ferments to create the "boiled sour" ingredient, which is then added to the final dough.
Why do they use it?
This technique is a hallmark of high-quality, "old-school" rye breads (like the Russian or German styles Bruno's emulates) because rye flour behaves differently than wheat flour.
Natural Sweetness: Boiling the flour converts some of the starches into sugars. This balances the harsh acidity of the sourdough with a mild, earthy sweetness.
Moist Texture: The scalding process gelatinizes the starches, allowing the bread to hold significantly more water. This is why good rye bread is dense and moist rather than dry and crumbly.
Shelf Life: The increased moisture retention and acidity help the bread stay fresh for much longer without artificial preservatives.
Summary
The "boiled sour" on the label is a scalded rye sourdough starter. It is a natural ingredient made from water, rye flour, and live cultures that gives the bread its signature moist crumb, slight sweetness, and complex sour flavor.
"Boiled sour" on the ingredient list made me think of a scald in a Baltic rye. But the scalds usually include a rye malt, which results in a dark rye. But this could have a scald that's rye flour only. I asked Google Gemini AI about the "boiled sour" - the response below seems plausible.
Some of the Baltic rye Formulas here Bread Formulas have scalds, always with rye malt and sometimes with some rye flour as well. If you don't want dark rye, try using rye flour instead of rye malt in the formula. The book "The Rye Baker", by Stanley Ginsberg is a great resource and is available as an e-book.
From Google Gemini:
The term "boiled sour" in the ingredient list for Bruno's sour rye is likely a translation for a key component in the sourdough process known as a scald or a porridge sour.
Here is a breakdown of what it is and why it's used:
🌾 What is a "Boiled Sour" (Scalded Mash)?
In rye bread baking, a scald (or boiled sour) is made by:
Boiling or scalding a portion of the rye flour (often coarsely ground or cracked rye) with hot or boiling water.
Allowing this mixture to cool and then fermenting it with a sourdough starter.
This initial cooking/scalding step is crucial because it gelatinizes the starches in the rye flour.
🧪 Why is the "Boiling" step important for Rye?
Rye flour has different properties than wheat flour, and the scalding process manages them for a better loaf:
1. Controlling Amylase Activity: Rye flour contains enzymes called amylases that, if left unchecked, can break down the starches into sugars too quickly during fermentation and the initial baking phase. This results in a sticky, gummy crumb. The high heat of boiling denatures (deactivates) these amylase enzymes.
2. Gelatinizing Starch: The heat causes the rye starches to gelatinize. This creates a more stable, gelatinous structure that helps the dough retain moisture and gives the final bread a moist, chewy, and non-sticky texture.
3. Enhancing Flavor: The scalding process helps to unlock and deepen the natural, malty sweetness of the rye grain, which then contributes to a more complex, mellow, and less harsh "sour" flavor after fermentation.
In short, the "boiled sour" is a cooked, fermented rye mash that is fundamental to achieving the characteristic moist, firm, and flavorful crumb of traditional, dense sour rye bread.
Try the recipes for Baltic rye breads on theryebaker.com website. I made the Latgalian Rye and it was fantastic! I also made the Palanga Rye but haven't posted it here. Both of the breads have scalds with pale rye malt but don't yield dark breads. And these are true scalds: the flour/malt/water mixture is heated for several hours until some (most?) of the flour is converted to sugars. These scalds aren't just pouring boiling water onto the flour.
The other contribution to flavor in the recipe is the combination of the scald with the a pre-ferment rye sponge. In the Latgalian Rye, this mixture is also heated which produces even more flavor. Yeast has to be added to make up for the diminished leavening of the sourdough.
These breads are more involved to make but reward you with exceptional flavor.
On a tour of the Baltics I felt right at home at the hotel breakfast buffets, enjoying smoked and pickled fish on rye; that's just what I eat for breakfast at home.
I don't think I have the patience to boil flour for several hours.
It takes a few minutes. I just made one of my own formulas using a scald and have scalded rye flour many times. You just pour boiling water over the flour and stir with a spoon until absorbed and let it cool off before using. You can put it in the refrigerator to speed up the process.
Yes, the scald is heated for several hours. Part of the problem is the term "scald" is imprecise. Some recipes use it to refer to the process you described. However, these are very different scalds from that process. These scalds (maybe brewing or Malzstück are better terms) are often found in Baltic, Russian, and some German recipes. The Russian websites I have browsed often refer to breads that use this technique as custard breads, and they are indeed creamy. The Latgalian Rye recipe is actually from the PCT LatvSSR 817-78 standard technical manual. Even Sergey at ХЛЕБ & ХЛЕБ was amazed by the bread.
In this technique, boiling water is poured over the rye flour but then a small amount (3–6%) of diastatic rye malt is added at 65 °C and maintained at that temperature for at least 1.5–2 h. It can also be done without the rye malt but the heating period needs to be longer. After several hours heating, the mixture is no longer a thick porridge but is a thin batter. The amylase in the malt/flour has converted a lot of the starch to sugar (mostly maltose).
I've used this technique in several of these Baltic and Russian recipes. I also have added some of this reserved (it freezes well) rye scald in whole wheat breads. It not only had the same effect as the scald you described, it also had a malty sweetness that I don't notice from a tangzhong/yudane. It really is worth trying this technique to experience the difference.
I am aware of those types of scalds as well. I was half asleep from getting up twice in the middle of the night to let my 4 dogs outside, so I didn't fully comprehend the comment :).
I can see how the scalds for these more complicated rye breads could put some people off. I was a recipe tester for the Rye Baker book, but I don't recall if I made any of these breads with more complicated scalds. I shall definitely have to give it a try in the future. I like your idea of freezing it and using it as needed or desired to experiment.
It's not that the term is imprecise, it's that not a whole lot of people understand that it's not a single thing, but a set of techniques each applied with certain goal in mind, not all of them applicable to every flour, and often resulting in barely distinguishable breads in simpler recipes.
Yes, these scalds are a little more involved. I found that the Keep Warm-Normal setting on a 3-qt InstantPot maintained a 63–65 °C water bath that made it a little easier for small quantities. For larger amounts, I have done the scald directly in the IP at the same setting.
The Latgalian Rye may be the best rye I have ever tasted, but I don't make it often because it is so involved.
Anyone have a clue about what "boiled sour" means? It's listed in the ingredients.
TomP
Nothing about the recipe but here's a piece in the Chicago Trib that's a paean to Chicago's breads (and yes, it mentions Bruno's) -
https://www.chicagotribune.com/1991/01/24/a-slice-of-life-6/
I didn't know anything about these places back when I used to live there (I left in 1972).
all the web references suggest they went out of biz around 2020. Here's a write up from 2011 -- https://www.newcity.com/2011/12/15/best-lithuanian-bakery/
Also: I really want their 'Famous SOUR RYE' neon:
Rob
ps: whaddaya wanna bet the boiled sour is a scald of whole grain rye later mixed with sourdough starter after it has cooled.
Based on baking science and traditional rye bread techniques, the "boiled sour" listed on the label is almost certainly a descriptive term for a specific type of scalded sourdough starter, known in German baking as Brühsauer.
It is not a chemical additive, but rather a natural pre-ferment created by a specific process.
What is "Boiled Sour" (Brühsauer)?
In traditional rye baking, "boiled sour" refers to a method where a portion of the rye flour is "scalded" (mixed with boiling water) before being allowed to ferment with sourdough culture.
Why do they use it?
This technique is a hallmark of high-quality, "old-school" rye breads (like the Russian or German styles Bruno's emulates) because rye flour behaves differently than wheat flour.
Summary
The "boiled sour" on the label is a scalded rye sourdough starter. It is a natural ingredient made from water, rye flour, and live cultures that gives the bread its signature moist crumb, slight sweetness, and complex sour flavor.
So basically a yudane.
Do the Japanese use rye? Apparently the technique works with wheat flour as well.
"Boiled sour" on the ingredient list made me think of a scald in a Baltic rye. But the scalds usually include a rye malt, which results in a dark rye. But this could have a scald that's rye flour only. I asked Google Gemini AI about the "boiled sour" - the response below seems plausible.
Some of the Baltic rye Formulas here Bread Formulas have scalds, always with rye malt and sometimes with some rye flour as well. If you don't want dark rye, try using rye flour instead of rye malt in the formula. The book "The Rye Baker", by Stanley Ginsberg is a great resource and is available as an e-book.
From Google Gemini:
🌾 What is a "Boiled Sour" (Scalded Mash)?
🧪 Why is the "Boiling" step important for Rye?
Try the recipes for Baltic rye breads on theryebaker.com website. I made the Latgalian Rye and it was fantastic! I also made the Palanga Rye but haven't posted it here. Both of the breads have scalds with pale rye malt but don't yield dark breads. And these are true scalds: the flour/malt/water mixture is heated for several hours until some (most?) of the flour is converted to sugars. These scalds aren't just pouring boiling water onto the flour.
The other contribution to flavor in the recipe is the combination of the scald with the a pre-ferment rye sponge. In the Latgalian Rye, this mixture is also heated which produces even more flavor. Yeast has to be added to make up for the diminished leavening of the sourdough.
These breads are more involved to make but reward you with exceptional flavor.
I have made https://theryebaker.com/black-rye-breadjuoda-rugine-duona-lithuania/ from the website but I mainly use his book. There are formulas from Lithuania, Latvia, Russia, and I think Estonia as well.
On a tour of the Baltics I felt right at home at the hotel breakfast buffets, enjoying smoked and pickled fish on rye; that's just what I eat for breakfast at home.
I don't think I have the patience to boil flour for several hours.
It takes a few minutes. I just made one of my own formulas using a scald and have scalded rye flour many times. You just pour boiling water over the flour and stir with a spoon until absorbed and let it cool off before using. You can put it in the refrigerator to speed up the process.
Yes, the scald is heated for several hours. Part of the problem is the term "scald" is imprecise. Some recipes use it to refer to the process you described. However, these are very different scalds from that process. These scalds (maybe brewing or Malzstück are better terms) are often found in Baltic, Russian, and some German recipes. The Russian websites I have browsed often refer to breads that use this technique as custard breads, and they are indeed creamy. The Latgalian Rye recipe is actually from the PCT LatvSSR 817-78 standard technical manual. Even Sergey at ХЛЕБ & ХЛЕБ was amazed by the bread.
In this technique, boiling water is poured over the rye flour but then a small amount (3–6%) of diastatic rye malt is added at 65 °C and maintained at that temperature for at least 1.5–2 h. It can also be done without the rye malt but the heating period needs to be longer. After several hours heating, the mixture is no longer a thick porridge but is a thin batter. The amylase in the malt/flour has converted a lot of the starch to sugar (mostly maltose).
I've used this technique in several of these Baltic and Russian recipes. I also have added some of this reserved (it freezes well) rye scald in whole wheat breads. It not only had the same effect as the scald you described, it also had a malty sweetness that I don't notice from a tangzhong/yudane. It really is worth trying this technique to experience the difference.
I am aware of those types of scalds as well. I was half asleep from getting up twice in the middle of the night to let my 4 dogs outside, so I didn't fully comprehend the comment :).
I can see how the scalds for these more complicated rye breads could put some people off. I was a recipe tester for the Rye Baker book, but I don't recall if I made any of these breads with more complicated scalds. I shall definitely have to give it a try in the future. I like your idea of freezing it and using it as needed or desired to experiment.
Regards,
Ian
It's not that the term is imprecise, it's that not a whole lot of people understand that it's not a single thing, but a set of techniques each applied with certain goal in mind, not all of them applicable to every flour, and often resulting in barely distinguishable breads in simpler recipes.
Yes, these scalds are a little more involved. I found that the Keep Warm-Normal setting on a 3-qt InstantPot maintained a 63–65 °C water bath that made it a little easier for small quantities. For larger amounts, I have done the scald directly in the IP at the same setting.
The Latgalian Rye may be the best rye I have ever tasted, but I don't make it often because it is so involved.
Thank you all very much. The Bruno bread had a lot of cracked or sprouted grains, which gave it a nutty flavor. Any ideas?
David