How to Create Flavour Part 2: Aroma

A guest post by Mel Barrett

Mel Barrett writes a regular cookery column for the Wholesome Food Association. Mel is a former management consultant who, since leaving the corporate world, has worked with butchers, bakers and canapé-makers (and many others too!) who share her passion for food produced with integrity. She has written/co-written publications for Sustain (the alliance for better food and farming) on bread and London’s food economy, and is currently developing a new kind of cookery course. She has two young daughters. To see Mel’s growing collection of cookery columns, click here.

This is the second of a special three-part series dealing with some of the basic science and chemistry of what makes food delicious.

Last month’s column (How to Create Flavour Part 1) explained the role played by sensors in our mouths and in our noses in determining flavour. The mouth detects salty, sweet, umami-rich, sour and bitter tastes, coming respectively from large molecules such as sodium chloride, sucrose, glutamate, citric acid and quinine; the mouth also senses piquancy (the heat from foods such as chillis). The nose detects odours, coming from much smaller compounds (for example, menthol in mint; eugenol in cloves) which float up from our mouths into our olfactory system.

These small compounds (referred to throughout this column as ‘aroma molecules’ or ‘aromatic compounds’) account for most of what we perceive as flavour. Their addition to our food is not always required: some dishes do very well obtaining their flavour from ingredients which primarily stimulate the mouth receptors. Think delicate scallops paired with a pea puree (sweetness) and bacon (saltiness); ramen noodles with spring onions (umami) and chilli (piquancy); tomato ragu with anchovies (saltiness and umami) and parmesan (saltiness and umami).

Generally though, most dishes benefit from the presence of aromatic flavours, which can serve to intensify a flavour already present in a foodstuff, provide an interesting contrast, or help to create a very specific character.

First, catch your aroma molecules…

There are four main sources of aromatic flavouring in the armoury of the domestic cook:

1. image by andrea 44

   Plants: The aromatic compounds found in herbs, spices, fruits and aromatic vegetables are contained in its essential oil, released by manual extraction (i.e. pressing, chopping , crushing, grating, grinding or simply by chewing in the mouth), heating (one reason why recipes call for the warming of spices prior to their use) or dissolving in a liquid.

   Aroma compounds are extremely volatile, meaning they evaporate when they come into contact with air (which is why most cookbooks recommend only grinding spices just before they are needed, and why chopped raw herbs pack a mightier punch than dried ones) and heat (one reason why stocks are simmered rather than boiled, and delicate herbs – basill, chervil, chives, coriander, dill, mint, parsley and tarragon – should be added towards the end of cooking). The herbs bay, marjoram, oregano, rosemary, sage and thyme are more robust, and can be added right from the start.

   Cooking food with aromatics in parcels of parchment or foil can help prevent the flavour molecules escaping.

2. image by dissemination

   Heat: When certain foodstuffs are heated at high temperatures without the presence of liquid, chemical reactions take place in which delicious new aroma compounds are formed. In foods in which both protein and sugar are present, even in small quantities (meat; fish; flour; some vegetables, for example onions and potatoes), reactions known as Maillard reactions produce delicious ‘roasted’ flavours, evidenced by an appetising brown colour.

   In foods containing high levels of sugar (for example apples) a reaction known as caramelisation produces nutty flavours (as well as an intense sweetness). The new aroma compounds, which typically only develop on the surface of the foodstuff (liquid in the centre of the food prevents the temperature reaching the required 154°C or over) sometimes end up in the pan instead of in the food, either because they have been released along with juices from the meat, or because food has got stuck to the pan.

   Reclaim these delicious molecules – by scraping them out, or by adding a liquid to the pan (wine, vinegar, water) in which to dissolve them (a process referred to in cookbooks as ‘deglazing’) – and you will never need to resort to a packet of gravy granules again! Salting meat or fish prior to cooking (using large flakes of salt, e.g. Maldon) helps a crust to form on the surface, which prevents some of the juices escaping into the pan (handy if you are not intending to deglaze).

3. image by gimmefood

   Fermentation: when a living organism (yeast, bacteria or mould) causes changes in a foodstuff, it results in the development of aroma compounds, some of which are very strong, as anyone who has eaten fermented soy beans (natto) can testify.

   These aromas require time to develop (for instance, bread which has been made the old-fashioned way is much more flavoursome than mass-produced factory bread, where industrial high-speed mixers and flour improvers have replaced long fermentation times), and become more complex if aging takes place in a container from which flavoursome compounds can further be absorbed, e.g. oak barrels.

   Of great use to the cook are fermented liquids, for example wine, vinegars, soy sauces and fermented fish sauces. Boiling wine for a period allows the alcohol to evaporate (along with water), thus concentrating the flavour (a process referred to in cookbooks as ‘reducing’).

4. image by public domain photos

   Smoke: a complex flavour source. Wood contains sugar and protein molecules, so both caramelisation and Maillard reactions occur when wood is burned, contributing flavour (see above). In addition, a variety of aroma compounds, including vanilla-scented vanillin and ‘smoky’-scented guaiacol, are created when other substances in wood are heated. Smoke is very effective at coating food; adding other aromatic compounds (in the form of sprigs of robust herbs, for example) to the fire over which food is hanging, or to the barbecue, is a good way of delivering flavour. Wood smoke does however contain some carcinogenic substances, so frequent consumption is not advised.

Then add them to the dish

There are two ways of adding aroma molecules:

1. image by jennifer

   The aroma source can be added directly to the dish. The flavour compounds stay in the original source, in other words, the flavour is imparted when the source – whether it be chopped herbs, grated lime zest or the browned crust on a piece of meat – ends up in the mouth. The source can be added prior to cooking (e.g. robust herbs rubbed over a joint of meat), or after cooking (e.g. delicate herbs). It can be mixed in to the dish (for example, pesto stirred through pasta and soups); layered, either on the surface (for example, sprinkled over stews, as the Italians do with the mix of chopped parsley, garlic and lemon zest known as gremolata), or inside a foodstuff (as with stuffings); or served on the side (as in Mexican salsas or the bowls of herbs placed with mezze on Middle Eastern tables).

   It can be added on its own, or combined with other ingredients, for example, oil to help it bind to the surface of a foodstuff; liquids and fats to help it thoroughly coat the surface of foodstuffs (for example herb butters); ingredients which add texture or volume (e.g. breadcrumbs in stuffings; pine nuts in pesto) and finally, ingredients which add taste (e.g. dried fruits in stuffings; acids in salsas and relishes).

   In order to deliver flavour in every bite, the aroma source must be able to cover a sufficient surface area, which can be achieved by adding in large quantities (although caution should be exercised with pungent flavours, for example many spices, raw garlic, ginger, sage and tarragon; milder spices, such as coriander seeds and fennel seeds, as well as most herbs, can be used with more carefree abandon); adding in very small pieces; delivering in a liquid; or bulking out with other ingredients.

2. image by rick

   Alternatively, the aroma source can be used to change the flavour of a foodstuff. The flavour compounds are transferred from the source to the foodstuff, in other words, the flavour is imparted when the foodstuff is chewed.To flavour a solid (e.g. a piece of meat or fish) it is simply a matter of allowing the desired aromatic substances to come into contact with the foodstuff. Meat absorbs flavour better when cold, as heat causes fibres to contract, forcing out juices, and preventing the absorption of substances. This can be done before cooking, via a marinade (a liquid, typically vinegar or alcohol, in which the raw foodstuff is left to soak), although, according to scientist Herve This, it takes one day for flavour in a marinade to penetrate meat to a depth of one centimetre.

   Another option is a brine, a salt solution in which liquid and flavour is transferred into the foodstuff (via a process called osmosis). After cooking, meat will continue to absorb flavours from aromatic stews (which is why stews are more flavoursome after a day in the fridge).
   To flavour a liquid it is simply a matter of adding the desired aromatic substances, and allowing time for the aroma compounds to dissolve. Herbs can be chopped into small pieces and dispersed throughout the liquid (adding colour and texture), or kept whole and removed once flavour has been imparted (for example, a bouquet garni, which is a tied bundle containing typically thyme, bay and parsley).

   Aroma compounds dissolve much more easily in oil, alcohol and vinegar than water, which is one reason why recipes usually sauté aromatics in oil first before adding stock, or use pastes (mixes of herbs and spices in oil). Oil and water don’t mix; minced vegetables, such as onion and carrot can help emulsify the two liquids (i.e. diffuse the flavoured oil throughout the stock), as can alcohol.

   Some aromatic compounds will dissolve in water-based stocks, however, sufficient time should be given for the flavour to infuse. (Too long, however, and flavour will evaporate! The secret is to keep tasting!). Liquids containing flour are less flavoursome, as the aroma compounds bind to the flour, preventing their evaporation.

So that’s Aroma. Look out next month for Part 3 in the series.

This column content (excluding images) © Mel Barrett 2011.

All images from Flickr, used under Creative Commons Attribution License. Click image to enlarge.