On food and cooking the science and lore of the kitchen ( PDFDrive ) 206

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On food and cooking  the science and lore of the kitchen ( PDFDrive ) 206

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Egg white foams are almost always made with other ingredients, and these can influence the beating process and the final consistency Salt Salt increases the whipping time and decreases the foam’s stability Salt crystals dissolve into positively charged sodium and negatively charged chloride ions, and these probably compete for bonding sites on the unfolded protein molecules, thereby reducing the number of protein-protein bonds and so weakening the overall structure It’s therefore best to add salt to the other components of a dish — the base of a soufflé, for example — rather than to the foam itself Sugar Sugar both hinders and helps foam making Added early in the process, it delays foaming, and it reduces the foam’s ultimate volume and lightness The delay comes from sugar’s interference with the unfolding and bonding of the proteins And the reduction in volume and lightness is caused by the syrupy sugar-egg mixture being harder to spread into thin bubble walls Slow foaming is a real disadvantage when the whites are whipped by hand — at standard soft-meringue levels, it doubles the work — but less so if you’re using a stand mixer The helpful thing about sugar is that it improves the foam’s stability By making the liquid thick and cohesive, sugar greatly slows drainage from the bubble walls and coarsening of texture In the oven, the dissolved sugar hangs onto the water molecules and so delays their evaporation in the high heat until after ovalbumin has had time to coagulate and reinforce the raw foam And it eventually contributes reinforcement of its own in the form of fine but solid, cottoncandy-like strands of dry sugar Sugar is usually incorporated into the egg whites after the foam has begun to form, when many proteins are already unfolded For some purposes, cooks will mix sugar and whites at ... By making the liquid thick and cohesive, sugar greatly slows drainage from the bubble walls and coarsening of texture In the oven, the dissolved sugar hangs onto the water molecules and so delays their evaporation in... molecules and so delays their evaporation in the high heat until after ovalbumin has had time to coagulate and reinforce the raw foam And it eventually contributes reinforcement of its own in the form of fine but solid, cottoncandy-like strands of dry sugar... disadvantage when the whites are whipped by hand — at standard soft-meringue levels, it doubles the work — but less so if you’re using a stand mixer The helpful thing about sugar is that it improves the foam’s stability

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