3. Food Chemistry and Reactions During Preparation

Introduction and Context

Cooking is not merely the application of heat. It is a controlled set of physical, chemical, and biochemical transformations that alter the structure, flavour, colour, aroma, texture, nutritional value, and safety of food. A chef who understands these transformations can move beyond recipes and make informed decisions when adapting ingredients, equipment, cooking times, temperatures, and service conditions.

Food chemistry is especially important in hospitality because the quality of a dish must be reproduced consistently at scale. A sauce may split, a custard may curdle, a cake may collapse, fruit may brown, or fried food may develop rancid flavours because of chemical conditions that were not controlled. Variables such as pH, temperature, water activity, oxygen exposure, concentration, agitation, and ingredient ratios therefore become operational as well as scientific concerns.

This chapter examines the principal chemical systems encountered in culinary production: acids and bases, water and water activity, colloids, emulsions, foams, gels, crystallisation, protein denaturation, starch gelatinisation, enzymatic browning, Maillard reactions, caramelisation, and lipid oxidation. These concepts are considered both theoretically and through professional kitchen applications.

Learning Objectives

After studying this chapter, students should be able to:

1. Explain the culinary significance of pH, water activity, concentration, and temperature.

2. Distinguish solutions, colloids, suspensions, emulsions, foams, and gels.

3. Analyse the mechanisms and control of denaturation, gelatinisation, browning, caramelisation, and lipid oxidation.

4. Diagnose common failures in sauces, baked products, confectionery, fried foods, and prepared dishes.

5. Select appropriate ingredients and processing conditions to obtain desired texture, colour, flavour, and stability.

6. Evaluate food-quality, safety, operational, and sustainability implications of chemical reactions.

The Chemical Environment of Food

pH and culinary control

pH expresses the acidity or alkalinity of an aqueous system on a logarithmic scale. A lower pH indicates greater acidity, while a higher pH indicates greater alkalinity. A change of one pH unit represents approximately a tenfold change in hydrogen-ion concentration. Most fresh foods are mildly acidic, although some vegetables, dairy products, meats, and processed foods occupy different parts of the pH scale.

Acidity affects flavour, colour, microbial growth, texture, protein behaviour, and enzyme activity. Lemon juice, vinegar, wine, yoghurt, and fermented products introduce acids into foods. Acids may brighten flavour, tenderise certain foods, reduce enzymatic browning, destabilise or stabilise proteins, and alter the colour of plant pigments. For example, anthocyanin pigments in red cabbage tend to appear redder in acidic conditions and bluer or purpler in alkaline conditions. Chlorophyll in green vegetables may become dull olive-green when prolonged heating and acidic conditions promote pigment changes.

pH is not interchangeable with titratable acidity. pH indicates the intensity of acidity at a particular moment, whereas titratable acidity indicates the quantity of acid that must be neutralised. Two foods may have a similar pH but different buffering capacities and therefore require different amounts of alkali to change their pH. In professional production, pH meters are useful for sauces, fermented products, beverages, and preservation systems, but they must be calibrated and cleaned correctly.

Water, moisture, and water activity

Water participates in dissolving, swelling, hydrolysis, heat transfer, and chemical reactions. The total moisture content of a food, however, does not fully indicate how available that water is for microbial growth or chemical reactions. Water activity, represented as aw, describes the availability of unbound water in a food. Pure water has an aw close to 1.00; dissolved salts, sugars, proteins, and other solutes reduce water activity by binding or immobilising water.

Water activity helps explain why jam, dried fruit, salted meat, and confectionery can be relatively stable despite containing moisture. Microorganisms require available water, and reducing aw through drying, salting, sugaring, or freezing can restrict growth. Water activity also influences crispness, caking, migration of moisture, enzymatic reactions, and oxidation. A crisp biscuit may become soft when it absorbs moisture from a high-aw filling, even if the biscuit has not gained much total water.

Temperature affects both reaction rates and water movement. Heating accelerates many reactions, while freezing reduces molecular mobility but does not stop all chemical change. During thawing, ice crystals melt and water may migrate, causing drip loss or loss of crispness. Food professionals must therefore control not only cooking but also cooling, storage, packaging, and service.

Food Structures: Solutions, Colloids, and Dispersed Systems

A solution is a homogeneous mixture in which substances such as salt or sugar are dissolved at molecular or ionic level. A suspension contains larger particles that may settle over time, as in some spice mixtures or flour dispersed in water. A colloid occupies an intermediate range: very small particles or droplets are dispersed in another phase and remain distributed because of Brownian motion and interfacial effects.

Many culinary products are colloidal systems. Milk, cream, mayonnaise, whipped cream, custards, sauces, ice cream, and bread dough all depend on dispersed structures. Their stability is influenced by particle size, viscosity, temperature, pH, surface-active molecules, and mechanical treatment. A change in one variable can cause separation, syneresis, curdling, collapse, or graininess.

Emulsions

An emulsion is a dispersion of one liquid in another immiscible liquid, commonly oil and water. In an oil-in-water emulsion, oil droplets are dispersed in a continuous water phase; mayonnaise, hollandaise, milk, and many salad dressings are examples. In a water-in-oil emulsion, water droplets are dispersed in fat, as in butter and some margarines.

Emulsifiers contain both water-attracting and fat-attracting regions. Egg yolk phospholipids, particularly lecithin, help stabilise mayonnaise and hollandaise by forming a protective layer around oil droplets. Proteins, mustard components, milk solids, and certain hydrocolloids may also contribute to emulsion stability. The smaller and more uniformly distributed the droplets, the smoother and generally more stable the emulsion, provided that the interfacial layer is sufficient.

Emulsions fail through coalescence, flocculation, creaming, or phase inversion. Coalescence occurs when droplets merge into larger droplets. Excessive heat, inadequate emulsifier, rapid addition of oil, insufficient agitation, or an unfavourable ratio of phases can produce failure. To make mayonnaise, oil is incorporated gradually into an aqueous phase containing egg yolk and acid while mixing creates small droplets. If a mayonnaise breaks, a fresh aqueous phase or egg yolk can often be used to re-emulsify it while the broken mixture is added slowly.

Hollandaise illustrates the importance of temperature. Egg yolk proteins must thicken the sauce without coagulating into curds. Excessive heat, prolonged holding, or poor agitation can cause curdling. A controlled water bath, gentle heating, and timely service are therefore more reliable than direct high heat.

Foams

Foams are systems in which gas is dispersed in a liquid or solid. Whipped cream, meringue, mousses, beer foam, and aerated confectionery depend on the formation and stabilisation of gas cells. Mechanical whipping incorporates air, while proteins or other surface-active substances migrate to the air–liquid interface and form films around bubbles.

Foam stability depends on protein concentration, fat content, viscosity, temperature, pH, sugar, and agitation. Egg-white proteins unfold at the air–water interface and create a stabilising network. Sugar can improve meringue stability by increasing viscosity, although it may slow foam formation if added too early. Fat interferes with egg-white foams because it disrupts protein films; even small amounts of yolk or grease can reduce volume. Whipped cream requires partial coalescence of fat globules to create a supporting structure, but over-whipping produces butter and expelled liquid.

Gels

A gel is a three-dimensional network that immobilises liquid. Gelatin, pectin, starch, agar, and hydrocolloids form gels through different mechanisms. Gelatin forms a thermoreversible gel as cooled collagen-derived chains create a network. Agar forms a firmer, more brittle gel and generally sets at a higher temperature. Pectin gels depend on pectin type, sugar, acidity, calcium, and concentration.

Gel formation requires suitable concentration and environmental conditions. Acid, enzymes, salts, heat, and sugar may strengthen or weaken a gel. Fresh pineapple, papaya, and kiwi contain proteolytic enzymes that can break down gelatin proteins; heating the fruit can inactivate these enzymes before it is incorporated into a gelatin dessert. Syneresis is the expulsion of liquid from a gel, commonly seen in poorly formulated jellies, custards, and dairy products.

Transformations During Heating and Cooling

Protein denaturation and coagulation

Proteins possess complex three-dimensional structures maintained by hydrogen bonds, ionic interactions, hydrophobic interactions, and disulfide bonds. Denaturation is the unfolding or alteration of this structure without necessarily breaking the primary peptide chain. Heat, acid, salt, mechanical agitation, alcohol, and enzymes can promote denaturation.

Coagulation occurs when unfolded proteins interact and form a new network. This explains the setting of eggs, the firmness of cooked fish, and the curdling of milk under acidic conditions. Denaturation is often desirable: it gives structure to omelettes, custards, cakes, and baked products. However, excessive heating may tighten protein networks, squeeze out water, and create toughness or dryness.

Egg custards demonstrate the importance of control. As egg proteins warm, they gradually thicken the liquid. If heated too rapidly or to an excessive temperature, the proteins coagulate into a granular mass and release water. Gentle indirect heating, adequate dilution, and removal from heat before over-setting produce a smooth custard. Salt and acids can modify protein coagulation, while sugar generally delays egg coagulation by competing for water and increasing the temperature required for setting.

Starch gelatinisation and retrogradation

Starch granules contain amylose and amylopectin. When heated in the presence of water, they absorb water, swell, lose their ordered structure, and release some starch molecules. This process is gelatinisation and is responsible for the thickening of sauces, soups, gravies, and pastry creams. The temperature range varies with starch source and composition.

Starch thickening is affected by agitation, acidity, sugar, fat, and the availability of water. Sugar competes for water and may delay gelatinisation. Fat can coat starch granules and reduce hydration. Prolonged heating or strong shear may weaken some starch-thickened systems. A roux controls starch dispersion by coating flour particles in fat before liquid is added, reducing lump formation.

On cooling, starch molecules may reassociate in a process called retrogradation. Retrogradation contributes to the firming of bread and the staling of baked products. It may also produce a desirable set in some puddings. Freezing and thawing can cause water separation in certain starch gels, so modified starches or alternative hydrocolloids may be selected for frozen food systems.

Crystallisation

Crystallisation is the organised formation of solid crystals from a solution or melt. Sugar crystallisation determines the texture of fondants, fudge, caramels, boiled sweets, and ice cream. Large crystals create a coarse texture, while small crystals may produce smoothness.

Supersaturation, cooling rate, agitation, impurities, and seed crystals determine crystal formation. In fudge, controlled cooling and beating encourage many small crystals. In clear boiled sweets, unwanted crystallisation is prevented through adequate dissolution, suitable glucose or invert sugar, clean equipment, and avoidance of sugar crystals on the pan wall. Ice cream quality depends partly on limiting ice-crystal size through rapid freezing and maintaining a stable frozen chain. Temperature fluctuations allow crystals to grow, producing a coarse or icy mouthfeel.

Browning and Flavour Development

Enzymatic browning

Enzymatic browning commonly occurs when plant tissues are cut, bruised, or peeled. Cell damage allows polyphenol oxidase to contact phenolic compounds and oxygen. The resulting quinones polymerise into brown pigments. Apples, pears, bananas, potatoes, and avocados are familiar examples.

Browning can be controlled by reducing oxygen exposure, lowering pH, cooling, blanching, or using antioxidants. Lemon juice combines acidity and antioxidant effects; ascorbic acid is particularly effective in fruit preparations. Syrups, vacuum packaging, refrigeration, and prompt processing also reduce browning. Enzymatic browning is not always undesirable: it contributes to the colour and flavour of some teas, coffee products, and fruits. The professional objective is control rather than total elimination.

Maillard reaction

The Maillard reaction is a complex series of reactions between reducing sugars and amino groups, usually accelerated by heat. It produces numerous flavour compounds and brown polymers called melanoidins. It contributes to the crust of bread, seared meat, roasted coffee, toasted nuts, and baked foods.

The reaction is favoured by moderate-to-high temperatures, relatively low surface moisture, suitable pH, and the presence of reducing sugars and amino compounds. A wet food surface remains near the boiling point of water until much of its surface water has evaporated, which is why drying the surface of meat supports browning. Alkaline conditions generally accelerate Maillard browning, whereas acidic conditions may slow it.

Maillard browning is distinct from caramelisation. It requires amino compounds as well as sugars, whereas caramelisation involves thermal decomposition and transformation of sugars. In practice, both may occur together in roasted and baked foods.

Caramelisation

Caramelisation is the thermal degradation of sugars at high temperatures. It produces a range of volatile aroma compounds, bitter or toasted notes, and brown pigments. Unlike the Maillard reaction, caramelisation does not require proteins or amino acids. The precise temperature depends on the sugar and the presence of water, acids, and other ingredients.

Caramel production requires careful heat management. Early heating dissolves sugar; later heating removes water and promotes colour and flavour development. Stirring may be useful initially but can encourage crystallisation after the syrup becomes concentrated. Cream, butter, or water added to hot caramel can cause violent boiling and must be introduced carefully. Over-caramelisation produces burnt, bitter flavours that cannot be corrected by dilution alone.

Lipid Oxidation and Quality Loss

Lipids provide richness, mouthfeel, cooking functionality, and flavour. They are also vulnerable to oxidation, particularly when exposed to oxygen, heat, light, metals, and large surface area. Oxidation produces hydroperoxides, which may later break down into aldehydes, ketones, and other compounds associated with rancid odours and flavours.

Unsaturated fats are generally more susceptible to oxidation than saturated fats. Repeatedly heating frying oil accelerates oxidation and may increase viscosity, darkening, foaming, and off-flavour. Food particles, salt, water, and metal contamination further reduce oil quality. Professional kitchens should filter oil appropriately, avoid unnecessary overheating, monitor colour, odour, smoke behaviour, and frying performance, and replace oil according to a documented standard rather than appearance alone.

Antioxidants, opaque packaging, oxygen control, refrigeration, and protection from metals can delay oxidation. However, antioxidants do not make poor storage acceptable. A comprehensive system combines suitable raw materials, stock rotation, temperature control, packaging, and sensory and analytical monitoring.

An Integrated Framework for Culinary Decision-Making

When diagnosing a food-quality problem, the chef or food technologist should ask five questions:

1. What is the dominant food system: solution, suspension, emulsion, foam, gel, or solid matrix?

2. Which variables are changing: temperature, pH, water activity, oxygen, concentration, time, or mechanical energy?

3. Is the intended change physical, chemical, biochemical, or a combination?

4. Is the reaction desirable, undesirable, or desirable only to a certain extent?

5. Which intervention will control the reaction without damaging safety, flavour, nutrition, or service efficiency?

This framework prevents superficial solutions. For example, a broken sauce may not require simply more whisking; it may require identifying whether the emulsion has overheated, whether the aqueous phase is insufficient, or whether the emulsifier has been diluted. Similarly, a soggy pastry may reflect moisture migration rather than inadequate baking alone.

Applied Case: Stabilising a Banquet Hollandaise and Protecting Quality

Background

An illustrative hotel kitchen prepares eggs Benedict for a 180-cover brunch. The hollandaise is made in batches and held for service. During the first service, several portions become thick and grainy, while others separate into a thin watery layer and a fat-rich layer.

Situation and analysis

The sauce is an emulsion in which clarified butter is dispersed into an aqueous phase containing egg yolk, water, and lemon juice. The grainy portions indicate excessive coagulation of yolk proteins, probably caused by prolonged holding at excessive temperature. The separated portions indicate emulsion instability, potentially caused by inadequate initial emulsification, excessive dilution, temperature fluctuation, or insufficient aqueous phase.

The kitchen also holds the sauce in a deep container. The outer layer cools while the centre remains hot, producing inconsistent viscosity and stability. Batch size and holding time are therefore operational variables, not merely recipe details.

Approach and solution

The chef adopts the following procedure:

• Egg yolks, water, and acid are whisked over gentle indirect heat until lightly thickened.
• Clarified butter is incorporated gradually while continuous agitation creates small droplets.
• The finished sauce is held in a shallow, temperature-controlled container rather than directly over heat.
• Small batches are replenished frequently, and the sauce is stirred at defined intervals.
• A written visual and sensory standard is established for gloss, pourability, acidity, and absence of curds or oil separation.
• Staff are trained to rescue a slightly broken sauce by preparing a small fresh yolk-water base and gradually whisking in the broken sauce.

Outcome

The revised process produces a more uniform sauce, reduces waste, and improves service consistency. Holding time is shortened, and the kitchen gains a measurable control point: temperature and batch age are recorded alongside sensory checks.

Learning points

The case demonstrates that food chemistry is linked to production design. Emulsion stability depends on formulation, droplet formation, temperature, time, equipment, and staff practice. A technically correct recipe can still fail if the holding system is unsuitable.

Challenges, Risks, and Professional Controls

Common culinary mistakes include adding acid or salt without considering protein behaviour, heating emulsions too aggressively, using insufficient water for starch hydration, allowing sugar crystals to contaminate a syrup, exposing cut produce to oxygen, and reusing frying oil beyond its functional life. Another mistake is treating a visible symptom rather than identifying the controlling variable.

Food safety must remain separate from sensory judgement. A sauce that looks acceptable may still have been held at an unsafe temperature. pH and water activity can support preservation, but they do not automatically guarantee safety. Hotels must follow applicable food legislation, validated recipes, allergen-control procedures, sanitation standards, calibration schedules, and documented temperature controls. Egg, milk, wheat, soy, nuts, and other ingredients involved in emulsions, gels, and baked goods must be managed within the property’s allergen system.

Accurate measurement supports governance. Calibrated thermometers, pH meters, refractometers, weighing scales, timers, and oil-quality tests can reduce variation. Digital kitchen-management systems may record cooking temperatures, cooling rates, batch numbers, and corrective actions. Data are useful only when measurements are valid and staff understand the decisions that follow from them.

Current Developments and Best Practices

Contemporary food production increasingly uses hydrocolloids, modified starches, high-shear mixers, vacuum processing, blast chilling, and controlled-atmosphere packaging to manage texture, oxidation, and shelf life. Spectroscopic and sensor-based technologies can support rapid assessment of colour, moisture, and oil degradation, although sensory expertise remains important.

Modern practice also emphasises sustainability. Precise control reduces rejected batches, overcooking, oil replacement, and unnecessary energy use. Using lower-temperature cooking where appropriate, recovering heat, selecting stable packaging, and designing menus around seasonal ingredients can improve both quality and resource efficiency. Novel plant proteins and alternative fats require careful evaluation because their protein, fibre, moisture, and emulsification properties differ from those of conventional ingredients.

Best practice is therefore a combination of scientific understanding and disciplined execution:

• define the desired texture, colour, aroma, and shelf life before selecting a process;
• measure critical variables rather than relying exclusively on intuition;
• control time, temperature, pH, moisture, oxygen, and agitation;
• standardise recipes while allowing informed adjustment for ingredient variation;
• validate processes at the scale at which food will actually be produced;
• record failures and corrective actions to support organisational learning.

Chapter Summary

Food preparation involves interacting physical, chemical, and biochemical systems. pH affects flavour, pigment stability, protein behaviour, enzyme activity, and preservation. Water activity, rather than moisture content alone, helps explain microbial stability, crispness, and moisture migration. Colloids include emulsions, foams, and gels, each requiring appropriate interfaces, networks, and processing conditions.

Heat denatures proteins and can cause coagulation; it gelatinises starch and may later contribute to retrogradation. Crystallisation determines the texture of confectionery and frozen desserts. Enzymatic browning occurs when enzymes, phenolic compounds, and oxygen interact, whereas Maillard browning involves reducing sugars and amino compounds. Caramelisation is the thermal transformation of sugars without requiring proteins. Lipid oxidation causes rancid flavours and is accelerated by heat, light, oxygen, metals, and repeated frying.

Professional control depends on identifying the food system, measuring critical variables, distinguishing desirable from undesirable reactions, and integrating scientific knowledge with equipment, staffing, food safety, sustainability, and service requirements.

Key Terms

pH: A logarithmic measure of hydrogen-ion activity indicating acidity or alkalinity.

Titratable acidity: The total acid quantity determined by neutralisation with a standard alkali.

Water activity: The availability of water for microbial growth and chemical reactions.

Colloid: A dispersed system with particles or droplets intermediate in size between a solution and a suspension.

Emulsion: A dispersion of one immiscible liquid in another, such as oil in water.

Emulsifier: A surface-active substance that stabilises an interface between immiscible phases.

Foam: A system containing gas bubbles dispersed in a liquid or solid.

Gel: A three-dimensional network that immobilises or holds a liquid phase.

Syneresis: The expulsion of liquid from a gel or semi-solid system.

Denaturation: Alteration or unfolding of a protein’s higher-order structure.

Coagulation: Formation of a protein network after denaturation.

Gelatinisation: Swelling and structural disruption of starch granules in water during heating.

Retrogradation: Reassociation of starch molecules during cooling or storage.

Crystallisation: Formation of an organised solid crystal phase from a solution or melt.

Enzymatic browning: Browning caused by enzyme-catalysed oxidation of phenolic compounds.

Maillard reaction: Heat-driven reaction between reducing sugars and amino compounds.

Caramelisation: Thermal decomposition and transformation of sugars.

Lipid oxidation: Reaction of fats with oxygen producing oxidation products and rancid flavours.

Hydrocolloid: A water-interacting polymer used to thicken, stabilise, or gel food systems.

Melanoidins: Brown, high-molecular-weight compounds formed largely during Maillard browning.

Review Questions

Short Answer Questions

1. Why is water activity more useful than moisture content alone when considering food stability?

2. Distinguish an oil-in-water emulsion from a water-in-oil emulsion and give one culinary example of each.

3. What is the difference between protein denaturation and coagulation?

4. State two methods of controlling enzymatic browning in cut fruit.

5. Why does repeated heating reduce the quality of frying oil?

Long Answer Questions

1. Explain how pH influences colour, flavour, protein behaviour, and enzyme activity in culinary foods.

2. Describe the formation, stabilisation, and failure of emulsions, using mayonnaise or hollandaise as an example.

3. Compare starch gelatinisation and retrogradation and relate both processes to sauces and baked products.

4. Differentiate enzymatic browning, the Maillard reaction, and caramelisation in terms of reactants, conditions, and culinary outcomes.

5. Discuss the chemical and operational factors that influence lipid oxidation in a hotel kitchen.

Analytical / Application Questions

1. A pastry kitchen reports that a fruit tart has a crisp crust immediately after baking but becomes soggy within two hours. Analyse the likely chemical and physical causes and recommend controls.

2. A chef’s chocolate mousse is dense rather than aerated. Using principles of foams, proteins, fat, and temperature, diagnose possible causes and propose a revised method.

3. A banquet kitchen experiences inconsistent gravy thickness after reheating. Evaluate the likely roles of starch, water availability, shear, temperature, and holding time, and design a control plan.

22. Multiple Choice Questions with Answers

Question 1

A chef wants to reduce browning of freshly cut apples. Which intervention is most directly effective?

A. Expose the cut surfaces to warm air

B. Apply an acidic solution such as lemon juice

C. Increase the surface pH with baking soda

D. Hold the apples uncovered at room temperature

Correct Answer: B. Apply an acidic solution such as lemon juice

Question 2

Which condition most strongly supports the formation of a stable mayonnaise?

A. Rapid addition of all the oil before mixing

B. Gradual oil addition with continuous agitation

C. Heating the emulsion to boiling point

D. Removing the aqueous phase

Correct Answer: B. Gradual oil addition with continuous agitation

Question 3

A custard becomes grainy and releases liquid. The most likely cause is:

A. Insufficient protein denaturation

B. Excessive heating causing protein coagulation

C. Complete inhibition of egg proteins by sugar

D. Crystallisation of salt in the custard

Correct Answer: B. Excessive heating causing protein coagulation

Question 4

What distinguishes caramelisation from the Maillard reaction?

A. Caramelisation requires amino acids and proteins

B. The Maillard reaction occurs only in acidic foods

C. Caramelisation is primarily the thermal transformation of sugars

D. The Maillard reaction cannot produce brown pigments

Correct Answer: C. Caramelisation is primarily the thermal transformation of sugars

Question 5

A crisp biscuit becomes soft after being stored with a moist filling. Which principle best explains this change?

A. Moisture migration caused by differences in water activity

B. Protein coagulation caused by oxygen

C. Lipid crystallisation caused by acidity

D. Caramelisation caused by refrigeration

Correct Answer: A. Moisture migration caused by differences in water activity

Question 6

Which action is most likely to improve the quality of a meringue?

A. Allowing traces of yolk to remain in the whites

B. Adding fat before whipping

C. Using clean equipment free from grease

D. Heating the egg whites to frying temperature

Correct Answer: C. Using clean equipment free from grease

Question 7

Starch gelatinisation occurs when starch granules:

A. Lose all water through drying

B. Absorb water and swell during heating

C. React only with oxygen at room temperature

D. Form fat crystals during cooling

Correct Answer: B. Absorb water and swell during heating

Question 8

Which factor accelerates lipid oxidation in frying oil?

A. Protection from light and oxygen

B. Repeated heating and contamination with food particles

C. Storage in a sealed, cool container

D. Reduction of the oil’s surface area

Correct Answer: B. Repeated heating and contamination with food particles

Question 9

A hollandaise separates during service after prolonged hot holding. The most appropriate diagnosis is:

A. The emulsion has been exposed to unsuitable temperature and time conditions

B. The sauce contains no dispersed phase

C. Caramelisation has converted the yolk into sugar

D. Water activity has become exactly 1.00

Correct Answer: A. The emulsion has been exposed to unsuitable temperature and time conditions

Question 10

Which statement about water activity is correct?

A. It is identical to total moisture content

B. It measures the availability of water for reactions and microbial growth

C. It increases whenever sugar is dissolved in food

D. It has no relevance to crispness or moisture migration

Correct Answer: B. It measures the availability of water for reactions and microbial growth