smart science: yeast edition

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We’re gonna chat about yeast – mostly because I’m still obsessed with bread (see here), but also because yeast is an important part of a lot of home kitchens. I’ve been working on getting a starter for sourdough going – so yeast thoughts are front and center in my mind. Let’s break this down.

To start, there is a difference between yeast and bacteria molecules. Yeast is a fungus. Bacteria are… bacteria. They have fundamentally different properties, extending from the presence of a nucleus, the organization of DNA and how parts of the cell are displayed. While bacteria can ferment, and produce some flavor molecules while they do, the fermentation of yeast is essential for leavening – or raising – bread. So very many factors can affect the fermentation of yeast – and therefore your final bread product.

  1. Fast or slow? Fast fermentation is desirable in terms of speed – you’ll get to your final product faster. However, for more complex flavors, a longer fermentation is definitely better. Different things can make a dough ferment at different speeds – and all of those factors are primarily what affects fermentation! It’s all about speed.
  2. The temperature of dough leads to a simple speed equation: the warmer the dough, the faster the fermentation… to an extent. If you put yeast in a hot enough environment (think, 140°F), they’ll just die, and no one wants that. Optimum fermentation temperature is 78°F-82°F. Below that temperature, our bacterial buddies are more favored for fermentation. If you put dough in a fridge to slow down the fermentation process, you can get strong sour flavors – because of the level of bacterial fermentation.
  3. The amount of salt can also affect the fermentation of yeast! See, we knew salt was important…. didn’t we. Salt slows down (retards) the ability of yeast to ferment. Salt also plays into bread importantly if you choose to do a pre-ferment, which is essentially pre-fermenting a chunk of ingredients before mixing your final dough. The timing of the pre-ferment can be manipulated through salt percentage. Additionally – the amount of sugar can affect how the dough ferments. Some sugars ferment quickly (think sucrose, glucose and fructose… all very common sugars), and some sugars ferment slowly, like maltose. Some barely ferment, like lactose! Different combinations of sugar types can affect how fast dough ferments. Some strains of yeast can grow very well in high-sugar environments compared to other yeasts – though for the home baker it’s usually just normal yeast doing its own thing. The challah bread pictured is a sweet and buttery dough, and my very normal yeast survived just fine in it.
  4. While it may seem obvious, the amount of yeast can affect the fermentation rate. Generally, the more yeast, the faster the fermentation. But, you have to toe the line with how much yeast you add, since too much can definitely add a rough flavor – think eating spoonful of yeast (gross). If you add too much yeast, your dough might also ‘exhaust’ itself: aka the yeast eats all the food in the dough and has nothing to do! Most recipes call for a smaller amount of yeast and a slightly longer fermentation time in order to offset this problem.

The coolest thing about all of this is once you get comfortable (and if you do, please tell me how, I’m still not 100% there), you can mess around with some of these variables (as well as pre-ferment times, fermentation times in general, and ingredients) to create your very own bread! We all should have the luxury of our own bread. Here’s some links to keep you reading:

  • Basic differences between bacteria and yeast…just a good fun fact to throw out at parties.
  • Breadmaking 101 on Serious Eats… talking all about proofing and yeast and fermentation and also mostly just about bread. We like that.
  • Wild yeast inspires thoughts of sourdough, and still follows the fermentation rules. Here’s a bunch of sourdough inspiration: a list of links within a list of links for all the bread pictures you want to drool at as well as helpful tutorials, troubleshooting, and recipes. Let’s all make bread!

Author: jess smart

blog owner at flourandgin.com!

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