Easter Bread Recipe - NYT Cooking

What Is Sourdough Starter Discard, And Why Should You Keep It?

© David Ferencik/Shutterstock two jars of sourdough starter

Sourdough is a delicious, hearty, chewy, bread that has marvelous depth of flavor. It's sour, sweet, and savory all at the same time. This type of bread is made with a sourdough starter that's a combination of flour, water, yeast, and bacteria. It ferments in the fridge for hours, days, weeks, months, and sometimes years.

Sourdough starter develops particular characteristics as it grows and changes, depending on where you live. San Fransisco sourdough, arguably the world's most famous kind, contains a special strain of yeast, called Lactobacillus sanfranciscensis, that isn't found anywhere else on the planet. The bacteria produces byproducts as it grows, including lactic acid, that give that sourdough its tang. (If you don't live in the Bay area, your starter will have different bacteria but will be almost as delicious.)

Sourdough starter has to be maintained because the yeast needs a consistent supply of food from the flour to keep growing. If you don't use the starter regularly, you must feed it, producing something called sourdough discard.

Why Not Discard The Discard? © Nabilah Zahra/Shutterstock plastic container of sourdough discard

When you revive a sourdough starter that hasn't been used in a while or refresh it without baking something, you remove part of the mixture and add more water and flour to the smaller amount so the yeast can grow and start to work again. Most instructions for refreshing starter tell you to throw away the mixture you removed, called sourdough discard. But MasterClass disagrees.

While you can't use the discard to leaven the recipe, the discard is full of wonderful flavor from the lactic acid and other byproducts the bacteria and yeast produce. You can scoop the discard out, put it in a separate jar or container, and store it in the fridge up to two weeks. (The discard won't be bubbly because the yeast is no longer active.)

Of course, sometimes the starter can't be saved. If there's any mold on it, you must throw it all away and start over. That goes for the discard, too. And if you see any pink or orange color, throw it all away. Some mold and bacteria can produce toxins as they grow that aren't destroyed by heat, so even if you bake the bread or pancakes or pretzels thoroughly, those toxins can still make you sick.

Use That Wonderful Sourdough Discard © Melissaberry/Shutterstock plates of tea and crumpets

Think of sourdough discard as a flavoring, the same way you would lemon juice or orange zest or mustard. There are recipes for banana bread, biscuits, scones, waffles, English muffins, naan, and even brownies and chocolate chip cookies that use sourdough discard. You can use sourdough discard in any recipe that has another source of leavening, as long as you think it could use some tang.

The Washington Post says that you can use eggs or baking soda as leaveners with the discard. The outlet also offers tips on replacing the liquid used in any dough with sourdough discard; it's not one-to-one as you may think.

King Arthur Flour has recipes for sourdough crumpets, which are like softer, spongier English muffins with lots of holes to hold melted butter. Sourdough scones are another delicious pastry option. And sourdough pasta? Why not? The possibilities are endless.

Read this next: Cake Hacks Every Baker Will Wish They Knew Sooner

Engineering Your Way To Better Sourdough (and Other Fermented Goods)

Trent Fehl is an engineer who has worked for such illustrious outfits as SpaceX and Waymo. When he got into baking, he brought those engineering skills home to solve a classic problem in the kitchen: keeping a sourdough starter within the ideal, somewhat oppressive range of acceptable temperatures needed for successful fermentation.

A sourdough starter is a wad of wild yeasts that you make yourself using flour, water, and patience. It's good for a lot more than just sourdough bread — you can scoop some out of the jar and use it to make pancakes, waffles, pretzels, and a host of other bread-y delights. A starter is a living thing, a container full of fermentation that eats flour and has specific temperature needs. Opinions differ a bit, but the acceptable temperature range for active growth is about 60 F to 82 F. Too cold, and the starter will go dormant, though it can be revived with a little love. But if the starter gets too hot, all the yeasts and bacteria will die.

While there are of course commercial products out there that attempt to solve this problem of temperature control, most of them seem to be aimed at people who live in some wonderland that never gets warmer than 80F. Most of these devices can't cool, they only provide heat. But what if you live in a place with seasons where the climate ranges from hot and humid to cold and dry?

The answer lies within Chamber, a temperature-regulated haven Trent created that lets these wild yeasts grow and thrive. It uses a Peltier unit to heat and cool the box as needed to keep the mixture fermenting at 26°C /78.8°F.

Thanks to the Peltier unit, Trent can change the temperature inside the chamber simply by alternating the direction of current flow through the Peltier. He's doing this with an H-bridge module driven by a Raspberry Pi Zero. When it starts to get too warm in the chamber, the fan on the outside wall vents the heat away. A second fan inside the chamber pulls warm air in when it gets too cold.

Trent says that Chamber performs really well, and he's recorded temperatures as low as 60F and as high as 82F. He mostly uses it for sourdough, but it could work for other temperature-sensitive food sciences like pickling, growing mushrooms, or making yogurt. We think it could be ideal for fermenting kombucha, too.

Chamber works well enough that Trent has put further development on the back burner while he makes use of it. He does have several ideas for improvements, so if you want to help, check out his website and Github repo.

Is It Safe To Eat Moldy Bread?

a loaf of bread with a red X over it

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Bread is a staple in many homes. Whether you're known for making Instagrammable avocado toast or like to assemble New York deli-worthy sandwiches, it's likely you keep at least a loaf in your kitchen at all times. Maybe you even keep a sourdough starter in your fridge so you can  bake your own loaves. No matter how much bread you eat, chances are high that you've probably forgotten about a loaf only to find it dotted with spots of mold. And it probably made you wonder—should I cut off the moldy parts of the bread and eat it? Read on to find out if moldy bread is ever safe to eat, how long bread lasts, and the best ways to keep it fresh.

Related: Is Bread Good or Bad For You? Nutritional Benefits & More

What Is Bread Mold?

Molds are fungi that may or may not be visible to the naked eye. If you see mold on food, that's just part of the story. That likely means that there's a large root network in the food itself: think of it like a network of blood vessels. The visible mold is made up of the mold's stalk rising up from the surface of the food with fuzzy spores attached. If you took a look at that moldy piece of bread under a microscope, the mold would look like little mushrooms popping up from the surface

Several types of mold grow on bread, including Penicillium, Fusarium, Aspergillus, Rhizopus and Mucor. Each kind of mold also has its own varieties, and each fungus species has a different spore color. To complicate things, the spores' color changes based on the fungus' life cycle and the surrounding environment.

Molds thrive in a moist environment, and mold spores spread through the air surrounding the medium it grows on—like that loaf of bread you left in your breadbox for too long.

Can You Eat Moldy Bread?

The simple answer is, no, please don't eat moldy bread. Whether the loaf of bread has one spot of visible mold or multiple ones, the bread is unsafe to eat. According to the USDA's Food Safety and Inspection Service, when you see molds growing on bread, it is likely that the root of the mold has infiltrated much of the loaf, no matter if the loaf is whole or sliced.

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With so many types of molds in the environment, there is no way to identify the type of mold (unless you have a science lab at home!) and whether the mold present is poisonous. So it's better to err on the side of caution and not to eat moldy bread to avoid getting sick.

Can I Just Cut Off the Moldy Part and Eat the Rest? 

Cutting off the mold you can see doesn't mean the bread without visible mold is safe to eat either. Since the root of the mold is deeply entrenched into the bread, with microscopic threads penetrated throughout, you can assume that there is a lot more mold than you can see. It is best to throw out the bread.

How Soon After Eating Moldy Bread Will I Get Sick?

Molds on bread may also produce a type of harmful toxins called mycotoxins. You may or may not get sick from eating moldy bread, but you can assume that the more moldy it is, the higher your chances are of getting sick. If you do eat moldy bread, you risk experiencing unpleasant symptoms, including nausea, vomiting and diarrhea.

In particular, young children, people over 65 years old, pregnant individuals and people with a weakened immune system should not eat moldy bread. Members of these groups could get seriously ill when they experience food poisoning.

Furthermore, according to the Centers for Disease Control and Prevention, people with poorly managed diabetes, and other conditions, may be more prone to getting infected by a rare but severe condition called mucormycosis after inhaling the spores of Rhizopus, a mold commonly found on bread.

More importantly, eating foods contaminated with mycotoxin may negatively impact gut health by destroying the beneficial bacteria and may elevate the risk of liver cancer, per a 2018 review published in Frontiers in Cellular and Infection Microbiology.

How to Keep Bread Fresh

According to the USDA'S Foodkeeper App, homemade bread can last up to three to five days in the pantry and two to three months in the freezer. To extend its freshness, using cloves, cinnamon and vinegar as part of the ingredients may prevent or delay mold growth, but obviously could change the bread's smell and flavor

Commercial bread, like a loaf packaged in a plastic bag that you'd find in the bread aisle at the grocery store, can last for about two weeks at room temperature, two to three weeks in the refrigerator and up to five months in the freezer from the date of purchase. Why can they last so much longer? These loaves are made with preservatives that inhibit mold growth.

Related: The Healthiest Types of Bread, according to a Dietitian

If you make homemade bread or buy a loaf fresh from a bakery while it's still warm, be sure to let it cool completely before covering it so you don't trap excess moisture on the loaf. And if you grab a slice of bread and discover moisture on the loaf, pat it dry with a clean towel or paper towel.

Bottom Line

Even if it hurts to do so, moldy bread should be thrown away because it's unsafe to eat, no matter how little mold is on there. Molds produce toxins that not only cause food poisoning but can also impact our health. If you only see a little bit of mold on a loaf of bread, that doesn't mean there isn't more that you can't see—it's likely that all of the bread is contaminated. Commercially baked loaves of bread have preservatives that inhibit mold growth, so they last longer than homemade bread. Use your freezer to extend bread's shelf life, and when in doubt, throw it out.

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