The Science of Baking: Air Pressure & Baking

How does air pressure affect baking?

As altitude increases, the amount of air pressure decreases. Another way to think about it is that the air is less dense. Think back to high school chemistry when you learned all about molecules. When heat is applied to water, it excites the water molecules and they begin to move around. As more heat is applied, they move around faster and faster and eventually overcome the bonds that are holding them together. Water begins to boil with the pressure inside the water exceeds the pressure outside the water (ie the air pressure.) So, the lower the air pressure the lower the boiling temperature of water. The weight of air, aka the air pressure, decreases by approximately 1/3 between sea level and an altitude of 10,000 feet. Because water starts boiling earlier, the delicate balance of ingredients in a baking formula is thrown out of whack because more water is evaporated before an item is finished baking. To keep the formula balanced, a series of changes must be made. See the chart below.

A general rule of thumb for baking at high altitudes:

  • Increase flour
  • Decrease baking powder
  • Increase eggs
  • Decrease sugar
  • Decrease fats
  • Increase liquids
3,000 ft
5,000 ft
7,500 ft
10,000 ft
Baking Powder Decrease 20% 40% 60% 80%
Flour Increase 2% 4% 10% 20%
Eggs Increase 5% 10% 15% 20%
Sugar Decrease 3% 6% 10% 12%
Fats Decrease 0% 0% 10% 15%
Liquids Increase 7% 15% 22% 30%

The Stages of Baking

In baking, the end result depends entirely on how accurately the ingredients are weighed/measured, how accurately the ingredients are mixed, and the type of pan and how it is prepared.

Cooks use recipes and bakers use formulas. Recipes can be adjusted and formulas, because baking is a science, are very specific.

Buying a scale is the best investment for successful baking. It allows for accuracy that just cannot and never will be obtained using volume (ie cups) measuring. Using a scale also reduces the number of dishes to be washed. Get a digital scale with a tare function and you can measure into a single bowl. Or, use a sheet of parchment paper and weigh dry ingredients onto it and use it as a funnel to pour into the mixing bowl. (I reuse the same sheet of parchment until it can’t take it any more.)

The rest of “mise-en-place” is the gathering and preparing of the equipment, including pre-heating the oven, lining the pans with parchment, gathering mixing bowls, bowl scrapers, spatulas, thermometers and whatever else the formula requires.

Once the exact correct amount of each ingredient is ready, mixing is next. It starts the chemical reactions that create the leavening in baked goods and creates the structure which will give the desired texture (large crumb, small crumb, tender, chewy, dense, light, etc.) once the baked good is cooled. If mixing isn’t done correctly, you won’t get what you want and you won’t find out until after the baking and cooling is completed.

The right amount of ingredients with the right amount of water combined in the correct method and baked at the right temperature results in successful baking.

The baking process is where the fruits of the all your precise labors will come to fruition. Lots of things happen in the heat of the oven and once the process has started there is nothing you can do.

  1. Yeast die (yeast can’t survive when exposed to temperatures above 140 degrees or so, which is why it is important to watch the temperature of the water used to dissolve the yeast or else they’ll kick the bucket before they even get started.)
  2. Fats melt
  3. Gases expand
  4. Starches thicken
  5. Protein coagulate/gel
  6. Water evaporates
  7. Enzyme reactions cease
  8. Browning takes place (caramelization or Maillard reaction)

Cooling is a really important part of the baking process too. All the components that became more fluid in the oven (fats, sugars, starches, proteins) need the chance to set in their final form. You worked hard to weigh and mix accurately and carefully. A little bit of patience to allow your treat to cool will be well worth the wait.

Stages of Bread Baking

  1. Mise-en-place (including scaling of ingredients)
  2. Mixing
  3. Fermentation
  4. Punching down (also known as de-gassing)
    (Be gentle- don’t beat or tear dough!)
  5. Dividing
  6. Rounding
  7. Benching (resting)
  8. Shaping and panning
  9. Proofing
  10. Baking (includes stippling and spraying)
  11. Cooling
  12. Storage

Stages of Baking (non bread)

  1. Mise-en-place (including scaling of ingredients)
  2. Mixing
  3. Panning
  4. Baking
  5. Cooling

Types of cakes (from “Cookwise”)

Regular Shortened and Classic Pound Cakes
  • Sugar </= flour (by weight)
  • Eggs =/> fat (by weight)
  • Liquids = flour (by weight)
High Ratio Cakes
  • Sugar >/= flour (by weight)
  • Eggs > flour (by weight)
  • Liquid =/> sugar (by weight)

Not all recipes published are accurate. Take a look at the weights and if they don’t fit these guidelines look for another recipe to adjust. Poorly written recipes are really frustrating and are nearly impossible to adjust.

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