Experiment
For our experiments the heating process was modified in the three parallels. The liquids were mixed and heated to a boil, whereby sugar and salt were dissolved into the liquid mixture. Mustard powder was then added to this mixture in three different ways:
Version 1: Mustard powder was added to the hot liquid mixture at 80°C and kept hot under cover for 15 minutes.
Version 2: The liquid mixture was cooled to 30°C, mustard powder was added and kept at this temperature under cover for 5 minutes. The enzymatic reaction was then stopped by quickly heating the mixture to a boil.
Version 3: The liquid mixture was cooled to 30°C, mustard powder was added and kept at this temperature under cover for 15 minutes. The enzymatic reaction was then stopped by quickly heating the mixture to a boil.
The panel was quite agreed in selecting the most and the least pungent mustard. Seven out of ten panel members picked Version 3, the mustard with 15 minutes incubation time with the enzyme, to be the most pungent. A few considered Version 2, the mustard with 5 minutes incubation time with the enzyme, as the most pungent, so these two mustards were perhaps not radically different in terms of pungency. The panel was unanimous in selecting Version 1, the one heated from the very beginning, to be the least pungent of all. This was verbally described as “least mustardy” with descriptions such as “beany,” “grassy,” “bitter,” and “not tasting of mustard.” They preferred the two first versions, described as “mustardy,” “balanced,” and with “good pungency/strength.”
What did we learn from this? At least, it became obvious that pungency in mustard can be significantly altered by carefully selecting the reaction conditions, time and temperature. You can prevent the development of pungency completely by heating, thus deactivating the myrosinase enzyme before it gets the opportunity to react. You can also fine tune the level of pungency by controlling the reaction time. In our case both the 5-minute and 15-minute versions were quite pungent. For a milder version, a significantly shorter time, say 30 seconds or 1 minute, might be quite sufficient before heating to a boil. Enzymes are undoubtedly sensitive, but quick if they first get the opportunity to react.
7
The Potatoes that Refused to Become Tender
Red bacalao hotpot is a peculiar dish in several manners. Firstly, it is both Norwegian and Spanish/Portuguese at the same time. In Norway it dates back to the 19th Century when cod traders from Europe introduced it. The dry-salted codfish, klippfisk, for the dish is definitely Norwegian, produced in western parts of Norway. In the high North, dry codfish, stockfish, can be dried by hanging them from wooden racks without the use of salt, but further south the humid climate makes it difficult to dry large fish without salting it heavily. The method for salting and drying the fish was imported by the Dutch trader Jappe Ippes around 1690. He taught Norwegians who lived along the Atlantic coast how to make the cod last months, in order to be transported by ship to southern Europe, South America, and the Caribbean Islands, much the same way as the Basques and Canadians of Newfoundland did. The other important ingredients of the red bacalao hotpot based on this saltfish are Mediterranean as well: tomatoes, pimientos (canned bell peppers), cayenne pepper, olives, and olive oil. This delicious dish would never have seen the light of day if we didn’t have an extensive cross-cultural communication!
Red bacalao hotpot
There exist many versions of this dish. Some families have their own recipes that are passed down through the generations. The recipe below is a fairly common version, enough for at least four diners.
Ingredients
900 g klippfisk (salt cod)
750 g potatoes, peeled and cut in 1/2 cm thick slices
2 large onions, sliced
3 red bell peppers or a can of tinned pimentos, diced in 1 × 1 cm pieces
2 dl olive oil
3 Tbsp. seedless black olives
4 cans (4 × 400 g) tinned tomatoes, preferably coarsely cut 2 cloves garlic, finely chopped
1 red chili (medium hot variety) finely chopped without seeds, or cayenne pepper to taste
2 bay leaves
2 Tbsp. parsley, chopped
Procedure
1–2 days before serving: After rinsing off excess salt under cold running water, cut the fish in 5 × 5 cm pieces and leave in cold water for at least 24 hours. A rule of thumb is 24 hours per cm thickness of the loin, changing the water a couple of times a day.
On day of serving: Sauté garlic, chili and bay leaves in some oil in a large pan. Starting with the fish, place fish, potatoes, onions, and peppers on top of each other in layers going several rounds of layers. Pour the tomatoes over this. Heat to a boil and let simmer gently until the potatoes are tender. Various recipes specify cooking times from 45 minutes to 1 hour 15 minutes. Shake the pan once in a while, avoid stirring. Garnish with good olive oil and parsley, serve with good bread.
Bacalao is a fairly common dish in northwestern Norway, and cooking it at home usually comes out well every time. As it is easy to prepare in large quantities at a time, it is also a common food when large groups of people are to be served. Bacalao is delicious and the cook succeeds with it almost every time. The most common failures are stirring too much so that the pieces of fish crumble, or to overcook it so that the potatoes turn mushy. The reason for the latter can be too long cooking time or a potato variety that is too mealy. Otherwise this dish is more or less foolproof.
Therefore, we were more than interested when hearing a story about a “bacalao failure” that was quite the opposite: a group of nonprofessional, but experienced, cooks had prepared a huge pan of bacalao to be sold at a school brass band festival. They started preparing the ingredients several hours beforehand, heating the stew for it to be ready when the musicians, parents and other spectators were to arrive. However, this time, the potato slices refused to become tender, even though they had been simmering for more than an hour! After all, cooking to the texture of al dente, slightly crunchy, is seldom what you aim at when boiling potatoes. What had happened?
About potatoes turning soft during cooking. The structure of a cooked potato is usually somewhere between mealy and firm (waxy). This is a result of both potato variety and cooking procedure. The mealy varieties, often deep fried or baked in the oven, commonly give mealy and even fluffy potatoes with a dry mouth-feel, whereas the waxy varieties, cooked in water, should feel moist and almost a bit juicy. However, most importantly, when we want to eat cooked potatoes we expect the interior to be soft, regardless of whether it is cooked in water or milk, fried in oil or baked in the air of the oven. A firm “crunchiness” usually indicates that the potato is raw, undercooked. Keep on cooking!
Potatoes soften during cooking when the starch granules inside the plant cells during heating take up water and swell—the starch gelatinizes. The cell walls also start to soften and cells originally glued together start loosening, or even detach, from each other. A major reason for the crunchy structure of the potato is this glue, pectin, located between the cells. If the pectin is strong and active, the cells are firmly attached to each other, and when you bite into it, it feels firm and even crunchy. A sensation that suits well when taking a bite of apple or carrot, but never for potato. Luckily, pectin is not soluble in cold water. If that was the case, potatoes and other fruits and vegetables would have started dissolving upon the first contact with water. Most likely, they wouldn’t grow to become vegetables and fruits in the first place. Pectin is, however, soluble in hot water, and when vegetables and fruits are heated the pectin is partially broken down and dissolved. Consequently, the cells loosen from each other and the potato becomes softer, and eventually breaks apart into pieces. When you bite into it, you break off groups of more or less intact potato cells. Taken to the extreme, all cells detach from each other and you have a potato soup. Even when baked in the oven, there is enough water in the potato itself to dissolve the pectin, but due to absorption of free water by starch granules and some water evaporation, ov
en-baked potatoes dry out along the way. The other extreme of a cooked potato is that the pectin glue remains strong and the cells remain tightly bound together. Thus, the teeth need to do the hard work and rip apart, or break up, the potato cells: the potato feels crunchy.
^ Granules and glue: Starch granules in potato are located inside the plant cells while the pectin is located outside, i.e. between, the cells and acts as glue.
The mystery of the persistent potatoes. Firm potatoes are recommended for bacalao because potatoes that are too soft would give a cloudy, mushy stew which is outside the style of the dish. However, even firm potatoes should be soft enough not to be felt as crunchy. At the brass band festival, the pectin apparently did not dissolve as planned. A food chemist would start looking for possible explanations to such a mystery. We envisaged at least three hypotheses to explain why potatoes in a bacalao hotpot would remain firm even after prolonged cooking.
Firstly, it is a well-known fact that softening of vegetables during cooking takes longer under acidic conditions. This is, however, not due to pectin but an important component responsible for rigidity of cell walls, namely hemicellulose. Since bacalao contains tomatoes, it is likely that the bacalao cooking liquid is acidic and might have retarded softening of the potatoes. But the potato problem in question first appeared at the festival using a fairly standard recipe, among experienced bacalao home cooks who had not experienced such problems previously. If acidity from tomatoes was the culprit, the cooks should have experienced this when cooking at home as well, and this should be a common problem cooking bacalao. It is not, and no recipes to our knowledge mention this as a potential problem.
The second possibility that occurred to us was the tendency of pectin to turn into a non-soluble form in the presence of certain metal ions from naturally occurring minerals, such as calcium or magnesium. Pectin, which, like starch, belong to the carbohydrates, is a long polymeric molecule where different organic acids and sugars form long chains. Under certain circumstances, the organic acids of the pectin chain can interact with calcium ions present in water. One calcium ion can interact with two acid groups to form bridges between the long pectin molecules. Such cross-links cause the pectin to form stronger networks making it less water soluble. When enough such bridges are formed, the pectin becomes practically insoluble, even in hot water. Vegetables cooked in calcium-rich media such as milk, cream, or hard water take longer to cook. They may even remain hard after very long boiling. Could it be that the water at the site was particularly hard, rich in minerals? We did not see this as a plausible reason because the water in the area is generally quite soft and some of the cooks indeed lived in the area and had not experienced this problem at home. But since we did not analyze the water, the hypothesis could not be completely ruled out.
The third hypothesis is closely linked to the previous one, but takes the cooking temperature into account. In plant cells there is a certain enzyme called pectin methylesterase, PME, which can cut off certain parts of the pectin molecule making it easier to associate with calcium. Pectin molecules are cross-linked to form networks, much like the hardening that occurs in glue (see illustration). The extensive pectin network becomes poorly soluble even in hot water, and the cells stay together resisting the teeth of the diners.
The optimal conditions for PME action are a certain temperature, ideally between 60 and 70°C, and the presence of calcium or certain other metal ions. Since calcium is present in all living cells, it is sufficient to keep the temperature between 60 and 70°C for a certain amount of time for the pectin to be hardened. Actually, PME works 100 times faster at 65°C compared to room temperature, so keeping potatoes at this temperature for 15–20 minutes is sufficient for the enzymes to do their job. Perhaps this was what happened with the persevering bacalao potatoes? Maybe the large pan took so long to heat that the potato slices were subjected to temperature and time for PME to crosslink enough pectin to harden the potatoes?
The experiment. We had three possible hypotheses. The first one was quickly falsified, so we didn’t find any reason to follow this line of inquiry into an experiment. The second, minerals such as calcium, was difficult to test because we did not have access to the water used in the mentioned case. However, follow us to the test of the third hypothesis and we will try to convince you that, in this specific case of bacalao, the second one can also be disproved.
We conducted the experiment as part of a food workshop at a Norwegian culinary school with culinary students, teachers, and other guests as participants. The teachers and students cooked three pans of bacalao based on the same recipe. Only one factor varied: the temperature and time in which the potatoes were cooked. In the first parallel, we cooked the bacalao the traditional way, exactly according to the recipe. In the second, we chose cooking time and temperature to deactivate PME. Since enzymes are a subgroup of proteins, and behave as such, they denature (and lose their ability to function) if subjected to higher temperatures, commonly above 70°C. The potato slices were therefore blanched: they were plunged in boiling water and cooked for four minutes, whereby they were transferred to ice water to stop the cooking process. The bacalao was then cooked according to the recipe using these blanched potatoes. In the third parallel, we chose conditions that should promote PME activity. The sliced potatoes were transferred to a pan of 65°C water and the temperature kept as stable as possible for 15 minutes, whereby they were used to cook bacalao according to the same recipe and procedure as the first two parallels.
The verdict. The three ready-cooked pans of bacalao were blind tasted by the workshop participants and evaluated according to several pre-defined criteria. We asked them especially to point out the two samples where the potatoes were hardest and softest, respectively. The taste panel of the day reported that the potatoes in the third parallel had the firmest potatoes. That was the one where we had attempted to promote PME action and reinforce pectin to achieve firm potatoes. This parallel was perceived as having the least crumbly and least smooth texture. The second parallel, where we had tried to deactivate the PME enzyme, was evaluated as having the softest, smoothest, and most crumbly potatoes. Indeed, we had got two extremes on the potato texture scale, while the bacalao cooked according to the classic recipe came out in the middle on all descriptive accounts. Our suspicion that PME was indeed the reason for the experience during the festival was considerably strengthened. The result would obviously not stand as a proper research study, but we had a fairly clear indication.
^ The hard potatoes of the bacalao: The enzyme pectin methylesterase (PME, red) modifies pectin (blue) so that it attaches more easily to calcium (Ca2+, green). The latter can bind two PME-chains at the same time, thereby forming a strong, hardened network. These potatoes will not become tender even after extended time in boiling water.
Usually we experience that cooking small pieces of food takes shorter than large pieces. However, occasionally the opposite may happen. A friend once wanted to speed up cooking potatoes by grating them into the smallest possible pieces. Surprisingly, the grated potatoes never became tender. It would have actually been quicker to cook them as whole potatoes. PME is most likely to blame for this, with grating enhancing the effect. In plant cells, PME and calcium are kept separate, located in different parts of the cells. But when grating the potato, cutting thin slices, or maybe even using a blunt knife, cells are broken and the two come in contact and can act even more efficiently to cross-link pectin and harden the potatoes. When boiling potatoes whole, the same happens because cells swell in warm water and some of them burst open. So, if your knife is blunt, you cut thinly, or grate a vegetable, be prepared for PME to firm up your food. If you don’t want this to happen, make sure the food meets high temperatures quite quickly. The mystery of potatoes refusing to soften is known in Finland as well. Many Finns are familiar with grandma’s advice that new (young) potatoes should be placed in the pot only after the water is boiling: “If you put new potatoes into cold water, they will never soften properl
y!” Fully grown may be put into the pot of cold water before turning the heat on. The reason for this phenomenon is the same as for bacalao: the pectin hardening enzyme PME. New potatoes, unlike stored potatoes, are still in their growing stage, as they are harvested early in the summer during the best growing season. In this stage, the enzyme activity is very high and the PME is also more active than in potatoes that have ripened and been stored during the harvest season. ×
Evaluating which is hardest or softest are rather descriptive criteria, not directly linked to one’s personal taste or preference. So, taste may indeed be used to make fairly objective evaluations and people are able to agree upon issues of taste if the task is clear and associated with something descriptive. However, when we asked which version of the bacalaos the participants preferred, the result was, as often, not as clear cut. Taste evidently differs among people, and, interestingly, the traditional way of preparing bacalao was the one to receive the highest number of votes. Who would have guessed. Science and analyses can explain, but often art or craftsmanship will produce what is most enjoyable.
8
Gravlax and a Pinch of Salt Chemistry
Microorganisms—yeasts, molds and various bacteria—are every-where in our environment. They are in the ground, in water and in the air. On the floor, on the table, and at the doorstep. On the skin, hands and under your nails. Microorganisms are on the surface of food, be it meat, fish, or plant product. Even the surface of each flour particle is populated by microorganisms. Fortunately, the vast majority of them are not harmful to humans, and many are even beneficial for us. However, they are ready to pop our food into their own mouths, insofar as microorganisms can be said to have a mouth. No wonder that fermentation, modification of foodstuffs by means of microorganisms, is so common in all parts of the world. In practice, all types of raw materials have been, or are being, fermented: fruits, vegetables, cereals, meat, and fish. Most likely, fermentation has been in use as long as humans have existed.
A Pinch of Culinary Science Page 6
