Friday, February 12, 2016

The Science Behind... storing your finished loaf

 Hey everyone, this is a quick final post for The Science Behind series on the bread baking process.  It continues where I left off with the last post about cooling, basically answering one main question (and a few smaller questions):

1. How should I store my bread to slow down staling and molding?
2. Why should I pre-slice my bread before I freeze it?
3. Why do different breads stale/mold at different rates?
4. What should I do if my bread gets stale / grows mold?

Let's go.

1. How should I store my bread to slow down staling and molding?

So far we've learned that during baking, sugars absorb tons of water and go all wiggly in a process called gelatinization.  When bread is taken out of the oven, the sugars push out the water molecules and slowly re-crystallize into a larger, more orderly structure.  The crust of your dough prevents most of the water from escaping as steam, but over time the water that is pushed out of the crystallized structure gets to the surface and is wicked away into the air, making the bread texture feel drier and drier.  Not all the water goes away, but the crystal structure makes the bread feel tougher and drier than it did when it was fresh.  The cooler the place you store your bread, the faster re-crystallization will take place, and the faster your bread will go stale.  This is particularly true in refrigerators, which circulate cool, dry air.

On the flip side, you have molding.  Bread molds because, as I mentioned above, the bread still has water trapped inside it.  Warm, moist conditions are optimal for mold growth.  If you trap the water inside or around the bread without giving it a way to get wicked into the air, mold will start forming after a few days.  If you leave your dough on the counter at room temperature, it will grow mold much more quickly than if you store it in the refrigerator.

But now we have a problem, don't we?  If you store your bread in the refrigerator, it will go stale faster.  If you store it on the counter, it will grow mold faster.

What to do?

You have three choices.

Option #1: Store on the counter, don't pre-slice it and eat it quickly.  My bread stays soft, but starts growing mold after a week on the counter in a plastic bag.  However, if I store it in a paper bag it doesn't mold but gets hard and dry.  If you are likely to finish your bread before the week is out, I would store it on the counter in a plastic or paper bag (pick your poison: quicker molding or tougher bread).  If you have a super crusty crust on your bread and want to avoid plastic bags, once you slice it, place it cut side down on your counter.  That way, the crust will prevent some of the water from wicking away.  You can't do this with breads that have a soft crust though. By keeping the loaf whole instead of pre-slicing it, you also delay some molding from occurring because it limits the surface area where mold from the air can settle, and the crust is less porous than the interior so mold doesn't spread as easily.

Another option for avoiding plastic is to wrap your bread in wax paper.  By using wax paper, you prevent water loss but still allow some ventilation so moisture isn't entirely trapped in and around your loaf.  However, I've found this sort of a difficult method of bread storage because you can't tape the wax paper shut like wrapping paper; you need to use twine or string, which makes it hard to unwrap and re-wrap.  Just a quibble.

While I don't typically store bread in wax paper, I think it looks festive when I give bread as gifts

Option #2: Refrigerate it, don't pre-slice it and wrap it tightly in plastic wrap.  By slicing your bread, you expose more of the surface area to the dry air of the refrigerator.  Leave it in loaf form.

Option #3: Freeze it, either as a whole loaf or pre-sliced.  This is probably the best way to keep your bread fresh for a long time.  Unlike in the refrigerator, in the freezer the water molecules freeze in place, keeping them from being pushed out by the sugar crystals.  Unlike the counter, the freezer isn't warm enough for mold to grow.  When you are ready to eat it, thaw the whole thing on the counter overnight or just take out a few pieces and toast them to thaw.

Obviously not a picture of a loaf of bread being frozen, but this is what I do every weekend.  I make a big batch of pancakes, then freeze them on a cookie sheet, then once they are frozen store them in a plastic bag.  Same principle as with the frozen loaf - I can take out just the number of pancakes I need, and by freezing them this way they don't stick together.

Ok, now for the smaller questions.

2. Why should I pre-slice my bread before I freeze it?  This is just another technique for lengthening the life of your bread.  By pre-slicing your bread before you freeze it, you can remove just the amount of bread you need without having to thaw the entire loaf.

pre-sliced and wrapped granola bars
3. Why do different breads stale/mold at different rates? You might have noticed that your baguette goes stale within a day while banana bread, whole wheat or challah takes much longer to go stale.

  • Enriched doughs last longer than lean ones.  This is due to added fats in the dough, particularly eggs and dairy fats, which get entangled in the sugar structures along with the water molecules during baking and delay re-crystallization.  If you want your lean dough to last longer, add a tablespoon or so of olive oil. 
  •  Sourdoughs last longer than breads made with commercial yeast.  Enzymes in sourdough delay re-crystallization more than commercial yeast.   If you want your bread made with commercial yeast to last longer, use less yeast and let it rise for a long time, ideally 12-24 hours.  That way there's more ethyl alcohol building up, and acid helps prevent staling.
  •  Whole grain breads last longer than white breads.  Whole grains contain bran and germ, which are harder for mold to digest than the refined sugars in white bread.   
  • Store-bought breads last longer than homemade breads. Commercial breads have added preservatives which extend the shelf-life of bread and keep it softer longer. 

Do keep in mind, though, that once again some of the same elements that delay staling speed up molding.  Moist dough = delayed staling but faster molding.  Longer fermentation = delayed staling because acidic, but it also more fully breaks down the organic material in bread so it is a readily accessible food source for mold.  Once again, pick your poison.

According to my research, here are some other antifungal (anti-molding) ingredients:
vinegar or other acids
coconut oil

unsulphured molasses
raisins- who knew they were antimicrobial?
sourdough starter (particularly the lactobacilli, which convert to hydroxy fatty acids)

4. What should I do if my bread gets stale / grows mold?  If your bread goes stale, there are a few ways to revive it.  Sometimes sprinkling it with water and microwaving it will make it soft for a very short while.  My suggestion, instead of trying to revive your stale bread, is to embrace it.
There is a multitude of ways to use stale bread, from croutons to french toast to bruschetta.

If your bread grows mold, like anything else soft that grows mold, discard it.  I used to think if you cut off the moldy parts that it was still ok to eat, but that is only true with hard cheeses.  the mold you see is only part of the organism.  Mold eats by first sending out root threads that digest the food, and these can reach deep into your bread.  While most people with healthy immune systems won't get sick by eating moldy bread, it's best to throw it away.

I hope you appreciate that in my discussion of mold, I did not include any pictures!

So that's it; the baking process as explained by science.  I hope you've learned a lot.  If you feel there's something I haven't covered, please feel free to leave a comment below.

My sources for this post:
the microbial shelf life of bread
Molds on food: are they dangerous?

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