Bubbles in bread – it’s just air but it matters

Bubbles are an integral part of myriad aerated foods, including breads, cakes, ice creams, and cereals.
Bubbles are an integral part of myriad aerated foods, including breads, cakes, ice creams, and cereals.PHOTO: THE STAR / ANN

(THE STAR / ANN) - Eggs, flour, salt, oil and … bubbles? It might not cross your mind to add it to your shopping list – and nor should it – but bubbles are an integral part of myriad aerated foods, including breads, cakes, ice creams, cereals, whipped cream, waffles, beer, Champagne and carbonated drinks. These can be aerated intentionally, or not.

Bubbles of gas are considered physical entities within the constituents of these foods, such as carbohydrates, fats, proteins, fibre and water.

Take popcorn, for instance – that is at least 95 per cent air. On a descending scale of aeration: rice cakes or puffed rice are 90 per cent air, baked loaves and cakes have up to 85 per cent air, hard ice creams are 50 per cent and soft ice creams are 28 per cent, while marshmallows are 75 per cent and aerated chocolate bars, 45 per cent.

These bubbles have been incorporated into the food using various techniques including simple whipping, mixing, shaking and frying, or more complicated technologies of pressure beating, gas injection, steam generation, extrusion, puffing, thermal expansion, vacuum expansion, dry heating and fermentation, or via the use of rising agents.

Bubbles in food are functional and may be considered an “ingredient”, since they lend a distinctive quality of texture, appeal and luxury, depending on gas content and bubble distribution.

Not only do they have to be cleverly incorporated and balanced during processing, they also need to be stabilised in the food’s final incarnation, so they can withstand transportation and serving.

Achieving stability

When it comes to bread loaves, the gas bubbles within are well-interconnected; they have a continuous gas phase within a porous network.

But with many other aerated food products, the challenge is one of stabilisation; for this, we assess aerated products according to the duration of time in which their bubbles should appear stable. These bubble stabilisation timescales range from seconds, to minutes, to hours, days, months and years.

bubbles and bread
Bubbles are an integral part of many aerated foods, including bread. PHOTO: THE STAR

We expect the tiny bubbles in Champagne to appear soon after pouring, just nice for the bubbles to rise from the bottom of the glass to the surface, to provide a tingling sensation as we sip.

The foamy structure of the creaminess of a milky coffees, or a fluffy meringue should be preserved from between minutes to hours.

The gas bubbles in an aerated chocolate bar should stay isolated as needed, since they provide that sensational melting effect in the mouth which a conventional, non-aerated chocolate bar doesn’t have.

In the manufacturing of aerated food, this stabilisation is aided by ingredients known as stabilisers, mostly emulsifiers.

In bread-making, the emulsifiers used are known as as dough conditioners, e.g. the diacetyl tartaric acid esters of mono- and diglycerides (DATEM, E472e) which help to strengthen doughs, and the distilled monoglycerides (DMG, E471) which act as dough softeners, while sodium stearoyl-2-lactylate (SSL, E481) has a bit of both functions.

The two emulsifiers that frequently show up on ice cream ingredients lists are the mono- and di-glycerides of fatty acids (MDG, E471), and Polysorbate 80 (Tween 80, E433).

Most food aeration processes use air or carbon dioxide, although specific applications do use other gases like nitrogen, argon and nitrous oxide. Nitrogen is also used as a blanketing gas in food processing, to slow down food spoilage due to oxidation.

A bubbly example: bread-making

Bread-making is a perfect illustrative tool for the aeration process, since it occurs in mixing, and in the expansion of volume during the proofing of the dough. Finally, the aerated structure is retained via baking.

During the (manual or mechanical) kneading process, a nuclei of gas bubbles up to eight per cent is incorporated into the dough. Any subsequent folding, punching, rolling, moulding and twisting that the dough may undergo won’t introduce any new bubbles, but will increase the number of bubbles by sub-dividing those already present in the dough – this is called “bubble break-ups”.

bubbles and bread
Kneading bread. PHOTO: THE STAR / ANN

Gas bubbles are also believed to be trapped within the dry flour particles, as they are added during mixing. These bubbles enlarge during the proofing of the dough, as fermentation takes place.

The carbon dioxide gas produced by yeast diffuses from one point to another according to the concentration gradient – moving from bubbles with a higher CO2 concentration or partial pressure to a bubble with a lower CO2 concentration or with a lower pressure.

The phenomenon by which smaller bubbles disappear and larger bubbles remain or continue to enlarge within the semi-homogenous viscous dough is known as disproportionation.

When two gas bubbles continue to expand up to a size large enough to merge and become one bubble, that’s called coalescence.

The coalescence of gas cells involves the rupture of the dough film between them, which results in the loss of gas and an irregular crumb structure. The complexity of these bubble dynamics eventually stabilises, as the foam structure of a fully-proofed dough with a void fraction of up to 80 per cent is sent to the oven for baking.

During baking, oven temperature will rise to about 180 deg.C. Starch gelatinisation (which begins at about 55 deg.C) and the coagulation of gluten protein (which completes at about 80 deg.C) has the dough setting into a sponge structure. The baked loaf will have a rigid shape, and can contain up to 85 per cent air.

The baked loaf will have a rigid shape, and can contain up to 85 per cent air. PHOTO: THE STAR / BLOOMBERG

Why bubbles matter

Objectively, aeration is all about increasing volume with no nutritional input. This helps in converting hard, tough, even gruel-like food into a lighter, more palatable form, which is more digestible.

It is also more appealing, from both sensory and aesthetic angles.

Texturally, aeration provides a sense of smoothness and luxury to ice creams, lightness to puffs, crispness to biscuits and fizziness to carbonated drinks. It also helps to reduce the intensity of flavours and enhance the perception of them, to trap aroma compounds and then release them for olfactory enjoyment.

Aeration may also alter perceptions of satiety, the feeling of fullness before food is eaten, when it is just viewed.

A group of scientists from the AZTI-Tecnalia Food Research Institute in Spain have worked closely with culinologists to design highly aerated products. They found that consumers experienced a higher level of satiety when presented with a highly-aerated product.

As Malaysian palates progress beyond hunger and even nutrition, that sense of luxury from aerated foods comes more sharply into the picture.

Scientific interchange

A group of 15 researchers from Malaysia braved the cold British winter in January this year, to attend a workshop on innovations in aerated food processing, along with 14 other researchers from Britain, under the Newton Ungku Omar Fund Researcher Links initiative.

I led the Malaysian team, which also comprised two mentors, 10 young lecturers representing local public and private universities, a researcher from the Malaysian Agricultural Research and Development Institute (Mardi), and another from the Malaysian food industry. Prof Grant Campbell from the University of Huddersfield, a world-renowned expert in food aeration, led the British team, who acted as mentors for our team.

bubbles and bread
A croissant is built by pockets of air bubbles using the lamination method; a perfect one can have 81 flaky, buttery layers of heavenly pastry. PHOTO: THE STAR / 123RF

The workshop was hosted by Campden-BRI, a famous food and drink research institute in the beautiful village of Chipping Campden, Gloucestershire; the institute supports the food and drink industries both in the UK and worldwide.

The workshop provided an excellent scientific platform for researchers to meet, share, learn, exchange ideas and discuss problems related to the creation of innovative food products using technologically advanced aerated food processing methods.

The researchers came from diverse backgrounds – there were food scientists, technologists, engineers, chefs, culinologists and industrialists.

Four keynote lectures covered everything from the fundamental principles of bubble creation in foods to innovative processing, structural measurement and the development of novel aerated foods.

Aimed at empowering the Malaysian food process engineering community to translate aerated food opportunities into businesses and markets, the workshop also strengthened scientific interchange and development between participants.

Participants also presented their own work on issues related to baked products, processing, ingredients, development, integration and enhancement.

Focus areas included bread production using other flours, such as rice and sweet potato, as alternatives to reduce our dependency on imported wheat flour, and the production of bread with an altered structure and texture by the modification of air-space mixing, to allow more widespread availability of affordable, high quality and healthy products.

Networking sessions helped to synthesise ideas and project plans including research collaborations and the possibility of running the Bubbles in Food 3 Conference in 2019.

A practical baking session was held in Campden BRI’s training laboratory, led by Dr Gary Tucker, head of baking and cereal processing.

Participants were able to knead and make bread by hand, then try using mechanical mixers under different conditions and formulations – which illustrated the complexity of the bread-making process with regards to mixer type, time and temperature as well as flour type, water levels, and functional and health-giving ingredients.

Baked products were subsequently evaluated (with much explanation) by Campbell and Tucker.


The Chorleywood Bread Process, which helped the UK to utilise its local wheat varieties, was much discussed at this point. Introduced in the 1960s, the process is known for its energy-intensive mixing, using the air-tight Tweedy mixer. This has an integrated pressure-vacuum system capable of reducing up to 85 per cent of the mixing duration of conventional mixers.

bubbles and bread
The Chorleywood process has helped Britain to utilise its local wheat varieties to make bread with improved volume and whiter crumbs. PHOTO: THE STAR

High pressure air is injected into the mixing chamber in the initial dough mixing process; towards the end, the vacuum is drawn very rapidly to make breads with improved volume and whiter crumbs, using local wheat varieties with moderate protein contents. The method and application has spread to other countries like Australia, Africa etc.

Bread engineering

It became very clear that bread-making – the aerated food process which is most well-studied – requires the widest field of knowledge for mastery, encompassing food science, technology and engineering. This spans everything from agricultural engineering for the growth and harvesting of wheat, to the mechanical engineering of mixers and energy efficiency of ovens, to chemical engineering for rates of heat transfer and bubble dynamics during mixing, proofing and baking.

Food engineering consolidates all these aspects and makes it relevant in industrial and manufacturing contexts. Bread-making requires so much science, the physics of bubbles, the chemistry of reactions, the biology of yeast and enzymes – and that’s not forgetting its still unexplained effects and behaviours, which are very much a part of the art of baking.

The workshop ended with a factory visit for the Malaysian delegates to Fine Lady Bakeries in Banbury, where we witnessed UK bread production lines, manufacturing and food traceability processes.

Ideas for tomorrow

After this fascinating, stimulating exchange project, we came home brimming with knowledge, ideas – and the enthusiasm to embark on new aerated food projects. These include the utilisation of composite flour from local resources such as sweet potatoes, by Mardi, and use of seaweed by Universiti Malaysia Sabah.

In Universiti Putra Malaysia, novel technology using the power ultrasound technique was found to have improved aeration in bakery products and have the potential to reduce the usage of emulsifiers.

Other projects involve the substitution of eggs, sugar or fats in baking recipes. Gearing towards the promotion of clean label food products for health promotion, this has also encouraged the growth of the niche artisanal breads and ice creams markets lately, with producers better able to manoeuvre ingredients and processes within a smaller scale production.