Characteristics of study population and data collection.

The study informants consisted of pork cooks divided into three groups: restaurant cooks (RC) of either sex (FC or MC), female home cooks of 18–39 years of age (YW), and female home cooks of 40 years of age and older (OW). The dividing of gender was imposed as it is usually (if not always) women who cook at home, and mostly (though not all) men cooking as a profession. The division on age at home was chosen based on the assumption that older women might cook differently from younger women.

In each village, approximately six (1–7) persons in each group were identified with help from the village chairperson, based on both purposive and snowball sampling (Table 1). These numbers were estimated as preliminary, but adjusted according to presence of informants, willingness to participate etc. The informants were coded for anonymity within the group by assigning a number to every person. This produced a unique identification code for each informant resembling Low-YW-03 or Fac-MC-01 and so forth. The majority of the informants were of the Safwa tribe (Table 1), originating in the area of Mbeya City. They are traditionalists and often believe in both traditional healers and acknowledged religions. The second most common tribal ethnicity was the Nyakyusa tribe, which originates from the Tukuyu area South of Mbeya. The traditional Nyakyusa people are agriculturalists often keeping larger amounts of milk-producing cattle and thus tend to include milk in their diets and cooking. The Ndali tribe originates from the southernmost areas of Tanzania, bordering Malawi and Zambia east and south of the study area, and the Malila tribe originates in the Northern Mbeya Region. The remaining tribal ethnicities originate from other areas of the country.

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Table 1. Characteristics and tribal ethnicity of 64 informants from the four study villages.

https://doi.org/10.1371/journal.pone.0274877.t001

A total of 64 interviews with cooks were performed and 14 direct observations were made of cooking situations, during which informal conversations took place. Cooking sessions with home cooks (all female) were participatory and took place in the homes of the cooks (Table 2); restaurant cooks were observed when working at the restaurant or at their selling point, according to Table 3. Furthermore, four interviews with slaughterers (who were also restaurant cooks) were conducted, as was one observation of a slaughtering session with the local slaughterer in a private village slaughter slab in Lowland Village. The observations and the informal talk during slaughter focused on the meat handling practices of the slaughter, and the fate of the various parts of the animal after slaughter.

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Table 2. Overview of number of interviews.

https://doi.org/10.1371/journal.pone.0274877.t002

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Table 3. Overview of number of observations of cooking sessions involving pork preparation.

https://doi.org/10.1371/journal.pone.0274877.t003

In the following, the term slaughterer is used for a person actually performing the slaughtering, where the term butcher is used for a person selling the meat in a designated meat shop, a butcher’s shop.

Throughout Tanzania, there is a tendency of pork restaurant cooks being male, which was echoed in three of the study villages (Mountain, Peak and Lowland Village). In Factory Village, however, there were clearly more female restaurant cooks in the village, which the gender distribution of participants from this village also reveals. We did not find any explanation for this.

Further data sources consisted of rich handwritten field notes from all interviews and all informal talks (at observations and at walk-and-talks) including drawings of particular situations or places, and photos of locations, infrastructure, water sources, village landmarks, or particular situations.

Guided interviews were conducted in Kiswahili through a female Kiswahili/English translator who was also fluent in several tribal languages. The PI of the study also spoke Kiswahili ensuring the accuracy of the translation. The interviews consisted of open- and closed-ended questions producing qualitative data as well as basic demographic data. This allowed the interviewer to probe and explore interesting points until saturation. The main questions included information on the recipe of the preferred pork dish, the preferred choice of meat and reasons behind, as well the sensory, cultural and traditional aspects guiding these choices. Furthermore, we explored the informants’ experience with “white nodules” (the chosen description of cysts) in pork along with their understanding of origin and implications.

To ensure the confidentiality of the informants of the present study, the authors cannot share the data forming background of the study. However, whenever data are needed for the transparency and validation of a finding, quotes and excerpts from interviews and informal talks have been included in the manuscript. In such cases, the informant has been anonymised.

Restaurants.

In the study villages, a pork restaurant constituted a pork-eating venue as well as a butcher shop or meat shop, as previously described by Kimbi [39]. Restaurants were situated in the village centre or market square and only sold pork. They were open on days where there had been a pig available to slaughter (or money to buy the pig to slaughter) and thus not every day. They are here termed “fixed restaurants”.

However, a restaurant was not necessarily tied to a specific location–it ‘followed’ the cook. In the study villages, there were daily small local markets offering vegetables, fish, and small cooking and household items, upon availability. Once a week, there was a bigger market in a larger village nearby gathering all the small markets in one place. Pork cooks from the small villages would travel to the larger market to sell pork dishes to the increased number of potential customers. In the case of Lowland Village, the female cook (Low-FC-02) would make her pork soup and carry it on her head walking to the market place every Wednesday. This type of mobile restaurant was often seen in the markets in the region.

Practices of cooking and handling pork in restaurants.

In the fixed pork restaurants were small piles of fried meat on a large plate alongside bigger piles of raw meat. The cooked meat pieces were approximately 5 cm cubes, had been dipped into the boiling oil to remove the blood from the surface of the meat (a practice called dipping). This dipping practice lasted less than a minute and was done to make the meat more visually attractive. The practice was observed at all participating restaurants selling fried pork. After dipping, the meat was put in a large dish to drain the excess oil. Customers would either buy the dipped meat or buy raw meat to take home. The raw pork pieces were displayed according to price and some negotiation was observed, because the cooks would decide what meat, fat and/or bone pieces to include in each pile. Only in one restaurant, a weight scale was used (Low-MC-01). The eat-in restaurant guests would order from the dipped meat and the cook would further cook the meat in oil until they deemed it thoroughly cooked. The pork was in most cases served with fried plantains (Fig 3).

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Fig 3. A restaurant workstation in Factory Village showing the three types of pork for sale in the restaurant.

On the right on the plate, plantains are seen alongside the dipped pork. On the left, the restaurant female cook is cutting the ready-to-serve pork and plantains on the wooden table where also the raw pork is located (in front).

https://doi.org/10.1371/journal.pone.0274877.g003

Based on observations in the restaurants, hand- and tool hygiene arose as a major issue for further investigation. The restaurant cooks were cutting the dipped and ready-to-serve pork and plantain directly on the table without cutting board or safe distance to the raw meat. This practice can be seen on Fig 3.

The restaurant cooks frequently would use the same knife for cutting raw and ready-to-serve meat. There were in total nine restaurant observations and not one cook washed or rinsed knife or hands during observations. The workstation would be superficially wiped with a cloth or apron to remove small raw meat pieces on the cutting area. There was water for hand washing present in all restaurants, but this would not be used to clean the workstation.

A point for potential transmission was observed when the cooks used the same plate to transport raw meat from the workstation to the fireplace, and then serving the meal to the customer after cooking. This practice of same-plate serving was observed in three out of nine restaurants.

All interviewed restaurant cooks knew not to serve undercooked pork, but few knew the reason for this (See Table 4). They knew that cooking it thoroughly was important because of health reasons and some even had explanations including parasites, but generally they had very different ideas of what was thorough cooking and how to measure it. During observations, one male restaurant cook explained he knew the pork was sufficiently cooked once it was “floating on the oil” with bubbles around the edges combined with his sensation of time passed (Low-MC-01). Another restaurant cook (Fac-FC-04) explained at observations that she “just knew” when the pork was done, but she could not explain why or how–only that she had cooked pork many, many times and therefore knew. This sense of “just knowing” was common at the observations in restaurants (and, in fact, in the homes too). Some mentioned the colour of the meat playing a small role, but most restaurant cooks “just knew” when the meat was thoroughly cooked. This showed the embodied knowing as something the cooks had learned through years of practice and repetition and therefore had gained a feeling—an understanding—of when the pork was thoroughly cooked. It was generally difficult or even impossible for them to explain this or provide the rationale behind their practices. None of the restaurant cooks used a thermometer, nor did they on any observation use some sort of time taking device.

Practices of cooking and handling pork in homes.

The home was a key site for preparation of pork and thus practices related to preparation and serving of pork in the home were important to analyse in the context of transmission.

Through interviews and observations, it became apparent that the dishes served in the home differed from the dishes served in the restaurants. Where the restaurants all served pieces of pork deep-fried in oil and served with fried plantain or chips, or a pork soup with plantains, the vast majority of the home cooks would make a thick pork stew with ugali (a common maize staple in sub-Saharan Africa consisting of maize flour cooked with water to form a stiff porridge). The younger home cooks would cook a plain thick stew with tomatoes and oil, where the older home cooks often would prefer to cook traditional stews from their tribal area (e.g. with plantains, potatoes, or cassava, as thick stews or more soup-like). At all observations of cooking sessions with the younger women, a thick stew was the recipe of choice. A few home cooks would explain cooking fried pork for their families but only on very rare occasions such as a good market day where the economic situation allowed this. One woman said in her interview:

“I always make stew with it [the meat], because the fried meat only, then it is not enough for the family”

Fac-YW-04

This excerpt did not stand alone and shows that the home cooks were cooking the stewed pork because it would stretch the meat compared to other recipes and thus feed the whole family.

During observations in the homes, there were situations that could potentially favour contamination. The women used the same knife to cut raw meat and vegetables and the same pot for washing raw meat and vegetables, albeit sometimes rinsing with water prior to use. However, in two of the five home cooking sessions, the women also served a side salad with raw vegetables washed in the same pot as the raw meat and cut with the same knife as the raw meat. In these situations, cross-contamination would be possible, as the cysts could transfer from the raw meat to the raw vegetables. The use of a cutting board was not observed, as all the women would cut meat and vegetables in their hands. Hands or knives were not washed between tasks, but wiped in a piece of cloth or in an apron.

At home, practices differ greatly compared to the restaurants. We found three main practices related to degree of heating/cooking meat in the homes that could be essential for potential transmission. These three practices were intertwined and a situation could contain several practices at the same time.

Uncertain cooking time.

The first practice of interest was the practice of estimating cooking time. The women were typically cooking a thick pork stew, as mentioned earlier. They would buy the raw pork at the restaurant and cut it up in pieces. These pieces were washed in water and transferred to the cooking pot using hands without wiping off remaining water. Some women would add a bit of water, some would not. The meat would fry in its own fat and the excess water. When this water dried out, the meat was typically put aside on a plate. In the same pot, the sauce would be made using tomatoes, onion and sometimes, other vegetables. The sauce would dry out quite a bit, leaving the desired thick stew. Then the meat was returned to the pot and heated, and the stew was thought to be ready. This ‘estimation’ of cooking time was an embodied practice that the women had learned through their CoP as women cooking at home. It was not just one embodied practice of cooking but also a whole perspective of practices of cooking, where the women do cooking. Several women expressed during interviews and observations that they knew that the meat was well cooked, when the water was dried up. This would not be a precise estimation, as the amount of water in a dish would vary. There was no particular time-taking or measurements of readiness of the meat present at any of the cooking sessions. One woman described the estimation as follows:

“I soft dry [the pork]. It still has its whitish colour; I just fry it very little. (…) I just check on the meat if it is cooked according to my satisfaction, then I take it out of the stove. But estimating time, I don’t know.”

Low-YW-03

This woman used the colour of the meat to estimate the level of cooking. Several of the women explained how they just knew when the pork was ready, but were not able to give an estimated cooking time–just like the woman in the excerpt above. Most women estimated the level of cooking based on a combination of: drying of water, the colour of the outside of the meat, the firmness of the pork pieces, her sensation of time passed, and her experience, in order to create a safe estimate of the readiness of the pork. Some women would bite into the pork piece, and return the remainder of the piece to the pot, if she was not satisfied. When the younger home cooks in Lowland Village cooked the stew during the participatory observations they cooked the pork pieces for more than 30 minutes, one for as long as an hour and a half. However, one must remember that they were cooking with us as guests, so it might not reflect the actual cooking time of an everyday meal.

The various practices of estimating the cooking of the pork had one thing in common–they did not have a distinct reference of time passed, but were all embodied tacit knowledge emerging from the practice of cooking. They had been learned socially in the CoP from when the women were young girls through repetition and later reproduction of the practices of “doing cooking”.

Lightly cooking of meat.

The second relevant practice was revealed during several interviews, informal talks and cooking sessions, where the women would describe how they would only lightly cook the meat. There were multiple reasons to fry only lightly and again, these could be intertwined.

When pork pieces fry in oil for a long time, they will shrink in size and become hard and dry in texture. The women would often cook the pork pieces only lightly to preserve the soft texture.

Several of the woman described how this was important for them in order to cook food that babies and people with bad teeth could eat. One older woman described this in her interview:

“I like soft meat because I have problems with my teeth” Peak-OW-04

This was a very common response to the question of whether they preferred soft cooked pork or dry cooked pork. The desire to preserve the soft structure of the meat was also important in families with children, as the babies could not eat hard fried pork. The woman expressed cooking soft pieces for the children:

“I don’t dry it, because if I dry it my kids will not be able to eat” Peak-YW-07

This was a common response from the women cooking at home. The children with only a few teeth had to be able to chew the pork with their gums and thus the meat had to be soft.

Another reason to cook the pork pieces only lightly proved to be of an economic nature. In order to make sure that the meat purchased was enough to satisfy the members of the household, the women cooked only lightly to prevent the pieces from diminishing through drying. One woman explains:

“The reason we like lightly stewed meat it is because we want the food to be enough and satisfy kids. Also small children they can’t eat dry meat” Low-YW-01

In an informal talk with an older woman living with her husband and six grandchildren (Low-OW-01), she explained how she would buy a small amount of meat and cut it into seven pieces–one bigger piece and six smaller pieces. The bigger piece was for her husband and the smaller pieces were for the children–she herself would just eat the stew with leftover scraps of meat and bone. She would only fry the pieces lightly, because neither the husband nor the small children had the teeth status for chewing dry meat–and they wanted the pork pieces to be as big as possible. This shows that cooks could engage in the practice of lightly cooking the meat for both reasons–to preserve the size and preserve the softness.

Fast cooking.

The last of the practices important to mention is fast cooking. Many of the women expressed a desire or need to cook fast. One woman explained in a cooking session that she normally cooked with charcoal, but when she was in a hurry, she would use the firewood stove, because the liquids would dry faster. Therefore, she knew the dish would be finished sooner. She also explained:

“You know, most people are in a hurry when they cook they don’t care much if the meat is cooked. We don’t have a constant time of boiling the meat. Maybe when we have time to settle and cook. When we are tired from the farm works, we are starving so we are in a hurry to eat, so time it is not an option” Muv-YW-01

She also mentioned the fact that there might be time to “settle and cook”, but that this was not the case in her everyday life. Here, she had to produce a meal fast in order to satisfy the family’s urgent needs. Another woman explained how she cooks “with ugali”, meaning cooking the thick stew and serving it with ugali:

“Most of the time I cook pork for lunch to eat with ugali because it is the fast dish or we order the meat which is already cooked from the restaurant. (…) Because it is faster” Fac-YW-02

This illuminates the need for cooking fast and why the women tend to cook the stew and not cook other, more time-consuming dishes. In many situations, the three main practices mentioned here were combined and the younger woman would lightly cook the pork pieces in a thick stew to produce a fast meal after a long days’ work in the farm.

A community of practice under change.

In the traditional CoP, the newcomers are the younger generation learning from the older. Indeed, the women cooking at home all learned from either their mother or another female relative. Only one woman explained that she did not have a mother nor had she lived in a family, so she learned from God and by looking at other people (Peak-OW-01). When asked, many of the women seemed surprised to even be asked of who taught them how to cook–the CoP of cooking was so innate and inherent to them that it seemed strange even to talk about it.

One younger woman from Lowland Village explained the CoP in her childhood like this–with a little grin—when asked who taught her how to cook:

“My mothers at home, of course, and groups of people like on the wedding ceremonies. I just watch how they cook and I learn by watching them” (sic) Low-YW-03

The term “mothers” refer to the cultural construction of the Tanzanian community of women and the familial construction of the older generation of women in the family. In Tanzania, if the father has more than one wife, the ones senior to your birth-mother are called “big mother” (in Kiswahili: mama mkubwa) and the junior ones are called “little mother” (in Kiswahili: mama mdogo). Furthermore, the term Mama is used as a sign of respect for women who have had children or who have reached a certain age, regardless if they are sisters or aunts. In fact, when a woman becomes a mother, her calling name changes to Mama followed by the name of her oldest child (for example Mama Joseph). This stays with her the remainder of her life and indicates the importance of children. After you have a child, you no longer keep your own individual identity, but gain the respected title of mother. The woman from the excerpt grew up among several mothers and thus learned how to cook from them. Women of different families meet and cook the meals for ceremonies (like weddings and funerals) and the woman in the excerpt also learned from watching these women cook together. The CoP in cooking is formed by these groups of women within the family and extends to the larger groups of women when families meet and cook together. This gathering of women from different families—cooking together, watching each other, learning from each other, add to the influences into the CoP. This is the traditional way of the CoP, from newcomer to old-timer.

Findings showed that there had in fact been a change in cooking practices in general through the last generation. Fig 4 shows the CoP under change with the influx from its members and their everyday lives. In the following, the different types of influx will be elaborated.

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Fig 4. The influx of new practices in an existing Community of Practice (CoP).

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Several older women explained how they learned to cook completely without oil, but either boiled the pork in water with salt or made a soup using groundnut, and potatoes or plantains. Soda ash (sodium carbonate, Na₂CO₃) was often added to the water to soften the meat. It is naturally occurring in the Tanzanian soil and is bought as a stone or as a powder in local markets. It neutralises the acids in the meat and breaks down the protein thus tenderising the meat while it is boiling. One older woman explained:

“My sisters taught me [to cook]. I was raised by my sisters since my mother died when I was very young. My sisters taught me to cook pork with salt and soda ash. The pork stew they also taught me but later on when they started cooking with tomatoes and onions” Peak-OW-03

We did not observe the use of soda ash during the cooking sessions, but we did see the soda ash for sale on the local markets indicating its use in households. Another traditional cooking ingredient was groundnut powder. It thickens the stew or soup and adds flavour and the three older women in the Lowland Village were cooking pork soup with boiled plantains with groundnuts or a smoked pork stew (using pork strips smoked over the fire for 2–3 days) with groundnut powder during the observations of cooking sessions. They explained that groundnuts were a common ingredient in their childhood home cooking, but had largely disappeared from modern recipes. The home cooks explained how this was the way their mothers, grandmothers or other female relatives would cook when they were young and living at home. Learning in the CoP of home cooks traditionally went from the older women to the younger women but always through women. Modern cooking in the home, as represented by the younger cooks during cooking observations in Lowland Village, consisted mainly of the thick pork stew. The younger women explained how their mothers or an older female relative had taught them how to cook all foods, except this recipe. One young woman explained:

“My mother taught me to cook, but pork she boiled with salt. I learned to cook pork like this from looking at friends.” Peak-YW-06

Even the older cooks had learned the recipe of the thick stew, but again, not from their mothers. They had learned this recipe from friends, neighbours, or their daughters. An older woman said her older children did not appreciate her traditional pork boiled in salt, so they taught her how to make the thick stew:

“[The children] were saying this meat doesn’t taste good like the fried meat and it is too soft, I decided to change the way I cook. I decided to fry first before I make stew, since then they enjoy my cooking”

Moun-OW-02

An older woman in Lowland Village, who had learned to cook the thick stew from her daughter, backed this up. During an informal walk-and-talk of her garden, she explained how her daughter had cooked it for her, she liked it, and now it was her preferred pork dish (Low-OW-04). These are examples of the changes in the direction of the learning and reproducing within the CoP.

The restaurant cooks had learned to cook the fried pork sold at restaurants from watching other restaurant cooks, typically by eating in restaurants, or by watching friends, who were restaurant cooks. One female restaurant cook had learned from her husband, who died suddenly leaving her with the responsibility of providing for the family. She knew how to cook fried pork so she continued his business after his death. Several explained how they saw a market and thus a business potential in cooking deep-fried pork and started based on that. One key informant (Low-MC-01) explained how he did not eat meat at all, but still he was the leading pork cook and slaughterer in Lowland Village. He said:

“For me what made me cook pork for business is the hardship of life, as youth when [you] reach a certain age you must find a way to get money. And I looked [at] what will be good for me to do. I started looking at my friends in town cooking, then I learned from them”. Low-MC-01

He had entered the trade because he had seen how it was becoming a steady trade in town while on a visit there, and decided to start his business in his own village–despite being a vegetarian himself. This indicates how the kind of trade is less important as long as it is economically profitable. This was the case for all the male restaurant cooks—they simply learned the trade out of necessity to fulfill the family’s needs as heads of their household and not because of a desire for cooking. One female restaurant cook in Lowland Village (Low-FC-02) cooked pig’s head soup and had started her business because the head is the cheapest part of the pig, but the rest of the female restaurant cooks sold fried pork like the male restaurant cooks. None of the restaurant cooks had any formal training, but all had entered the CoP due to the economic potential of the trade. None of the restaurant cooks mentioned having learned the recipe of fried pork from their mothers or female relatives. This is probably due to the fact that the fried pork is a modern recipe and that the community of practice of women cooked other traditional recipes.

It seems the element of travelling was also important to how the cooks learned new recipes. Several of the villagers explained how they travelled to town and tasted the new recipe of thick stew here. One young woman explained:

“[I learned to cook the thick stew] at a restaurant in town.” Low-YW-02

This was backed up by an older woman, who learned through her husband’s travels:

“My mother taught me how to cook the old-school way boiling and adding salt only. My husband told me how to cook the modern way of drying the meat. He saw it somewhere in town and told me how. Then I just tried.” Moun-OW-04

Furthermore, several of the restaurant cooks explained how they had learned to cook in town at a restaurant. One male cook explained:

“I was working in a restaurant in town and I learned by looking at the cook cooking the stew” Fac-MC-05

These excerpts are examples of how travelling is an important element in the acquisition of new inputs into the CoP. The villagers of Mountain Village had to travel by foot to a nearby village for market day or onwards travel, but Factory Village and Lowland Village had daily minibuses passing through, connecting them with nearby towns. Albeit infrequent, uncomfortable and slow cheap daily transportation to bigger villages or towns makes it entirely possible to travel and thus the acquisition of new practices, recipes and ideas into the CoP of cooking continues. Travelling has also changed the availability of food, making rice available for even mountain residents although it grows in warmer climates of less altitude. In traditional cooking in the study area, they did not use many vegetables. An older woman explained:

Woman: We didn’t have tomatoes in those days, even to get an onion was a miracle, it was hard to get them. Interviewer: So the only ingredient you were using in those days was the salt?

Woman: Yes”. Moun-OW-02

This was an important finding as infrastructure and transportation is becoming more and more extended and thus the availability of ingredients will expand as well.

In conclusion, the findings reveal the main potential transmission points of T. solium taeniosis in the rural kitchens of Southern Highlands of Tanzania. They showed that the pork cooks would undercook pork in certain situations, and that the poor hygiene standards might play a role in transmission. Moreover, they showed that the pork cooks, both restaurant and home cooks, would act in a way that made sense to them in the particular situation. If that meant cooking lightly, in a different way or selling undercooked pork, then that is what they would do–because it made sense in that particular set of circumstances. They would be guided in their choice of practices by the particular circumstances in combination with the inherited and embodied knowing of how to cook pork.