Since it seems like you are getting your info from the books you own could you cite the page references?
Absolutely. The following references are from "Sous-vide Cuisine", Joan Roca/Salvador Brugués, Montagud Editores S.A.
Original title: La Cocina al Vacio
First published in 2003 by Montagud Editores, S.A.
©Third English edition: Montagud Editores, S.A. 2007
©Joan Roca and Salvador Brugués
©Montagud Editores, S.A.
Copyright Registration: B-26942-2007
ISBN: 978-84-7212-112-6Chapter 3. Sous-vide Cooking , p.51
“We can broadly define cooking sous-vide as heating the food previously sealed in an airtight and heat-resistant container whose atmosphere has been modified ( a vacuum has been produced,, with or without elements such as gases, liquids, etc.).”Chapter 3. Sous-vide Cooking , p.76
“ In the vacuum, the atmospheric pressure acting on the packaged product causes the water to vaporize before it would in the conventional cooking, in which pressure does not have as great of an impact on the final result (this means that the food will experience the effects of water vaporization at lower temperatures, along with all consequent modifications). This is therefore a very important fact that distinguishes sous-vide cooking from traditional methods.”
“ Pressure is one of the fundamental principles on which sous-vide is based, since it what allows a vacuum-sealed product to cook at low temperatures. Nonetheless, it remains a subject seldom studied by cooks-even though they have an inkling of its vast possibilities, the still don’t use it as a fundamental principle when cooking or intentionally seeking positive alteration of foods.”Chapter 3, Sous-vide Cooking/ Technical Fundamentals p.84
“Our aim is to discover the why and how of the sous-vide cooking system through the analysis of the following parameters:
- Oxygen-free atmosphere
- Airtight containers and effect on pressure
- The time/temperature relationship
THE OXYGEN-FREE ATMOSPHERE
In this section we study a factor that plays a crucial role in cooking foods and, as a result, in their final quality… One of these potential alterations, … ,is oxidation, a reaction that occurs when oxygen bonds with other elements in food. Let us remember that these alterations manifest themselves in changes in color, odor, flavor, in its organic properties, etc.
When we cook sous-vide, and thus without oxygen, we prevent these reactions.4
… Another area affect by a lack of oxygen is enzymatic reactions, because the enzymes’ behavior is inhibited."Bottom of the page, left corner, light grey font:
“4. The majority of food reactions are hydrolysis or oxidation; therefore, these reactions must be slowed to preserve or improve preparations. One way of doing this is to eliminate one of the reactants ( in this case oxygen).”Chapter 3, Sous-vide Cooking/ Technical Fundamentals p.85
“AIRTIGHT CONTAINERS AND THE EFFECTS OF PRESSURE
COOKING SOUS-VIDE WITH THE EFFECT OF PRESSURE
Pressure has a fundamental effect on foods and provides a series of advantages in preparation that would be difficult to attain by traditional methods. The bag in this case acts as a second skin or direct protection for the ingredient ( especially in the case of shrink bags) and subjects it to constant pressure.
The main functions of the airtight containers are:
1. To support or hold the ingredient’s natural structure so that it does not break apart (e.g., foie gras).
2. To exert equal pressure over the entire surface of the ingredient. This evens out the cooking time for many ingredients (e.g., asparagus).
3. To prevent changes in weight from the ingredient drying out during cooking, thanks to the airtight container and the use of low temperatures.
4. To stop aromas from volatilizing, thereby enriching the preparation. The container helps to lock in the ingredient’s natural flavors; in fact, it serves the purpose of closing pores. This also occurs in cooking by concentration, but here there is no need to apply high temperatures that could denature or alter the ingredient’s initial flavor.”
“Sealing in shrink bags: guaranteed pressure” (highlighted in grey, upper left corner ,p.85)
“ All vacuum-packaged foods are subject to exterior pressure due to the absence of air in the bag. Sous-vide preparation sometimes requires the product to remain under pressure during the cooking process. Certain ingredients subjected to high temperatures during sous-vide cooking do release water vapor due to the heating of their own water.6 The bag then undergoes some interior pressure, causing it to lose some of the effect we are looking for.”Middle of the page, footnote, highlighted in grey:
”6. In sous-vide conditions, water vapor forms at much lower temperatures than in normal atmospheric pressure conditions.”
I don’t know if a definition of vacuum is even needed at this point, but according to The American Heritage® Dictionary of the English Language (Fourth Edition copyright ©2000 by Houghton Mifflin Company. Updated in 2003. Published by Houghton Mifflin Company. All rights reserved.):
vac•u•um (v k y - m, -y m, -y m)
n. pl. vac•u•ums or vac•u•a (-y - )
a. Absence of matter.
b. A space empty of matter.
c. A space relatively empty of matter.
d. A space in which the pressure is significantly lower than atmospheric pressure.
I hope this answers most of the questions we have discussed this week.
Edited by MikeTMD, 10 May 2008 - 08:35 AM.