post

Volumetric or Ready Mix

What’s The Difference? 

Concrete is, without a doubt, one of the most common construction materials. This is because it can be used for a wide variety of projects. It is essentially a blend of water, Portland cement, and aggregates. The two basic types of concrete used in the construction industry are site-mixed concrete and ready-mix concrete. 

There are slight differences between these two types of concrete. It is important to be aware of the differences, even if they seem subtle to you, as doing so can make it easier to choose the right concrete for your project. Here are the major differences between site-mixed and ready-mix concrete:

Preparation 

One of the obvious differences between these two types of concrete is the way they are mixed. Ready-mix concrete is usually manufactured at a plant and delivered to the clients in a ready-to-use state. It’s typically sold by volume, which is measured in cubic meters. 

Site-mixed concrete, on the other hand, is prepared at the client’s construction location. The components are mixed in specific ratios to achieve different degrees of strength. When making this type of concrete, caution must be taken to avoid quality issues. 

Time

If you are working on a time-conscious project, it’s obvious that speed is important. In such a case, you should choose ready-mix concrete, as it’s easier to load and off-load, which may save you time.

Volumetric concrete is more time consuming to work with, as you have to pause part of the project while the mix is being created. 

Equipment

An important factor for any construction project is your equipment and where you can source what you need. Volumetric concrete requires the use of equipment such as batch mixers. Whereas, ready-mix concrete does not require the project owner to hire equipment, as the concrete is not made on-site.

Convenience

Ready-mix concrete is convenient for almost any kind of construction project, as it can be delivered to multiple sites within the project location. However, volumetric concrete has to be mixed as close as possible to the point of use to avoid contamination. 

Another major difference between ready-mix concrete and volumetric concrete is storage requirements. You will require controlled storage space for the materials used to make volumetric concrete. However, when using ready-mix concrete you won’t need any extra storage space. 

Quality

Ready-mix concrete has a better and more consistent quality when compared to site-mixed concrete. This is because ready-mix concrete is mixed in an automated and controlled environment. 

Material takeoff

The materials used to make site-mixed concrete have to be estimated individually and purchased separately. However, ready-mix concrete is simply calculated as a single item. 

Waste 

Working with site-mixed concrete causes material loss not only when the materials are being mixed but also during storage. Whereas, ready-mix concrete causes minimal waste on your site because the concrete is delivered in a ready-to-use state. 

Workforce

When working with ready-mix concrete, the only time you may require skilled labour is when pouring and compacting the concrete. However, you will require more man-hours when working with volumetric concrete.

In summary,  

Both types of concrete have some major differences. It is important to research which type of concrete is best for your construction project. Generally, ready-mix concrete is a better option as it can be used for a wider variety of projects.

if you have any questions make sure to contact us.

The post Volumetric or Ready Mix first appeared on Base Concrete.

Did you miss our previous article…
https://www.thevisualconcretegroup.com/?p=311

post

Phytodepuration with Degre.47

Depurating Landscape: an introduction to plants as a water treatment alternative

This article is a collaboration between Degré47 and Critical Concrete, aiming to be an introduction to phyto purification’s general concepts for self-constructors. It also aims to shed light on these systems as low-cost, low-tech and self-constructible wastewater treatment solutions. 

Degre.47 Logo

The wastewater issue 

It isn’t new to argue that the disorganized and centralized population growth in urban areas has brought challenges to the natural environment. In addition to CO₂ emissions, waste production and impermeabilization of soil, wastewater is one of the fundamental issues local governments need to address. At the very least, the wastewater from human activities of any sort needs to be treated to be assimilated by nature. 

There are many water treatment solutions, from the collective to the individual scale. One of the most common sanitation solutions in urban centres is a collective one: wastewater treatment plants. These centres manage the wastewater through physical, chemical and biological processes in a complex and highly specialized infrastructure. [1] 

After the physical filtration through decantation, flotation, filters and/or membranes, traditional treatments commonly make use of chemical products, notably coagulants (ferric chloride, aluminium sulphate, etc.), flocculants, and sometimes disinfectants such as chlorine or ozone. These processes, however, are arguably costly and energy-intensive, not to mention polluting. They also necessarily generate by-products such as coarse waste, sand and sludge that must be cleaned, decanted, stabilised and treated. [2] 

In addition, in the ever-growing urban centres, many areas aren’t able to access the public sewage system, bringing up the importance to think of alternatives for wastewater treatment, especially low-cost and low-maintenance ones, as the mismanagement of effluents can pose a serious issue to natural hydric resources. [3]

Individual or small-scale collective sanitation solutions might be a good way to tackle the situation. A solution that stands out is the phyto-purification system with its low energy and low maintenance (as there’s no need for emptying and transporting). It is already the main sanitation system in France for cities of less than 1,000 inhabitants. [4]

This system, which is based on the use of plants (phyto) to filter the wastewater has been proving to be a low-cost yet highly efficient way to treat domestic wastewater. Because it is energetically and logistically autonomous, phyto-purification can be considered an ecological sanitation solution. 

Purification with plants 

Phyto-purification consists of wastewater purification systems that make use of aquatic plants, reproducing water depuration processes typical of humid areas. There are two main methods of phyto purification: lagooning, which consists of ponds with microphytes, similar to natural wetlands, and the filters planted that make use of macrophytes and consist of ponds filled with aggregates in which the water circulates for treatment. [5]

In these systems, the plants are responsible for bringing oxygen through their roots whereas the aggregates act not only as a physical filter — as bigger particles can’t penetrate it — but also as a chemical filter as they absorb phosphorus and ammoniacal nitrogen. In these basins, an important biological process also occurs: the microfauna present in the system degrades organic matter, turning it into nutrients to be absorbed by the plants. [6]

The interesting aspect is that, although the name might indicate, the wastewater is not filtered by the plants. In reality, the plants are the key element to create the environment for bacterial activity, especially in the region around the plants’ roots. The plants greatly benefit from the system as it absorbs nutrients that are liberated in the process of depuration. It’s a symbiotic relationship.

The different methods

There are two groups of phyto purification systems that can be used according to different needs and types of wastewater: lagooning and filters planted. [7]

Lagooning 

This system makes use of microphytes (small aquatic plants), microorganisms and (sometimes) substrate to control water pollution. Its main characteristic is the resemblance with natural wetland areas in which the majority of elements are saturated, i.e submerged in water. [8] 

In this model, the main purification process occurs on the aquatic surface where the plants and the bacteria present in their roots are located.  In this solution, the effluent is continuously supplied and homogeneously distributed on the surface, flowing horizontally and superficially at low scooping velocity. The water is then collected by a drainage pipe located in the basin’s bottom. [9]

It is important to stress that in this solution, the substrate is not a requirement, and when not applied, fluctuant aquatic species should be used (see image 1). [10]

 

fig. 1: Different types of plants

 

Because there’s no emphasis on physical filtration with a substrate, this solution requires a previous treatment focused on the removal of organic matter and suspended solids as it mainly targets the removal of nutrients, especially phosphorus by the plants and bacteria. [11] The use of a substrate, however, can be beneficial if residual suspended solids end up in the basin. 

This is a cheap and very low maintenance option, however, it generally requires a larger area than other methods. 

 

fig. 2: surface flow filter with substrate and emergent plants 

Filters planted 

In this model, the system works through percolation, meaning the wastewater infiltrates the substrate in the process of purification. Here the substrate can be saturated or not. [12] 

In this system, the water flows under the surface of the planted bed, through the pores of the substrate. There are two subsurface models: the horizontal flow filter and the vertical flow filter.

 In the horizontal model, the flow can be operated in a continuous input, intermittent or even in batch mode whereas the vertical flow model requires intermittent dumping of water in short periods, followed by long resting intervals. 

 

fig. 3: subsurface horizontal flow filter

The long periods between inflow in the vertical flow basin results in a high rate of oxygen transfer from the atmosphere to the system. In aerobic conditions the nitrification can occur, potentiating the nitrogen. In the horizontal flow basin, the poor levels of oxygen favor the occurrence of denitrification by anaerobic bacteria. [13]

 

fig. 4: subsurface vertical flow filter

In some cases, both flows can be combined to enhance the system’s performance. That’s the case of the double planted filter method applied by Kevin Quentric and documented and published as a tutorial by low-tech lab. [14]

It consists of two different units with a vertical and a horizontal water flow that perform complementary tasks in the process of depurating the wastewater. 

 

fig. 5: section of double filter planted 

The first phase of this system is a 60-80 cm² deep vertical filter (VF) which is divided into two parts and each part takes turns receiving the raw sewage (wastewater without previous treatment) from above (see fig. 6). The wastewater spreads on the surface of the first filter and has its solid particles such as hair, fat, faeces, etc, drying and decomposing on the surface whereas the water infiltrates downwards until it reaches the gravel layer. It might sound like the perfect recipe for a smelly garden but, as Kévin explained in emails to us, in a nutshell, bad smells occur in warm, low oxygen environments, when the water stagnates and fermentation takes place. In this double filter planted, however, the vertical filter is in open air, meaning it’s fairly oxygenated. The coarse material retained on the surface of the sand dries out and compost whereas the wastewater quickly infiltrates, without time to ferment. For this, the occurrence of smells is rather rare. 

After the percolation, the water then is collected by a drain in the bottom of the VF. This phase of the process is aerobic: the bacteria present in it require oxygen to mineralize the organic particles making the compounds absorbable by the plants. 

 

fig. 6: plan of double filter planted

The second part of the system, the horizontal filter (HF) is 60cm deep, filled with gravel and water 10 cm below the substrate. The second filter is then a poorly oxygenated environment, in which anaerobic bacteria live. These bacteria perform the important task of denitrifying the water by extracting the oxygen from the nitrate molecules, turning them into dinitrogen.

Another interesting aspect is that this system is energetically autonomous. For that, it relies on gravity: each stage into the water purification is lower than the previous one so the water can flow without the use of pumps. 

The step-by-step for this method can be found on the low-tech lab site. [15]

Pretreatment

In the double planted filter by Kevin Quentric there’s no need for primary treatment and the raw sewage can be discharged directly on the first filter. In some models, however, pretreatment is required before the wastewater discharge for removal of coarse particles and settleable solids in order to prolong the useful life of the systems, minimising the occurrence of clogging. 

The specific type of pretreatment depends on the type of sewage and on the chosen method of phyto purification. Some of the primary treatment methods are:

Screening: This is typically the first step, especially for surface flow filters. Screens are used to remove large debris. [16]Oil removal by decantation: The method is based on injecting fine air bubbles into the grease tank, allowing the grease to rise quickly to the surface (grease is hydrophobic). [17]Sedimentation: Water is typically retained in sedimentation basins for at least 4 hours, allowing particles to settle out. [18]

Domestic phyto-purification

The management of wastewater is of extreme responsibility but depending on which system is chosen and the knowledge of the builders, self-construction is an accessible and plausible option. In addition, professionals in the field can provide help for those seeking to build their own phyto-purification system at home.  

When planning a phyto-purification system, some things must be taken into consideration, such as sizing, site and botanical species. 

Choosing a site

Ideally, the system should be located as close as possible to the sewage outlet. Remember to make sure the system works with gravity by building it on a slope or working with built and excavated basins. Earthwork is also an option but it might significantly increase the costs of the construction. In the elected site for construction, the soil should be sufficiently compacted to minimise groundwater infiltration and should be above the water table and floodplains.

Another aspect to have in mind is that phyto purification requires space. The site of construction should be of sufficient size to meet current and possible future expansions. Also, insects (especially on surface flow models) and, very rarely, odours can pose discomfort. Therefore, make sure the system is not too close to your and/or the neighbour’s house.

Lastly, the site should be very accessible to construction and maintenance machines and vehicles. [19]

Sizing

The dimensions of the system should be calculated by maximum capacity and a good way to do so is using the value of “inhabitant equivalent”, which relates to the house’s number of rooms and not to the number of inhabitants. In this model, each room of the house = inhabitant equivalent (2 to 4m²). [20]

Plants

To choose what species should be used, a few criteria need to be taken into consideration such as main pollutants to be removed; climatic conditions and local availability of species. They can be emergent, fluctuant or submerged species (see fig. 01). [21] 

In Europe, the common reed (Phragmites communis) is one of the main wetland plant species used for water treatment, especially on subsurface flow filters. Some examples are Caltha palustris,Veronica beccabunga and the Typha latifolia. 


fig. 7: Phragmites communis, Caltha palustris,Veronica beccabunga and Typha latifolia, respectively.

When the water goes through a pretreatment basin, the plants in the filter basin can be less resistant. Some examples are the Sparganium erectum, Alisma plantago and Iris pseudacorus. [22] Before mixing different species in the same basin, research about possible interactions between the species and if there is competition between them.


fig. 8: Sparganium erectum,Baldellia ranunculoides and Iris pseudacorus, respectively. 

It’s advisable to transplant seedlings of plants that have been removed from a nearby location, which are naturally more adapted to the local climate and to do so in the rainy season, in order to minimise conditions of hydric stress for the plants. Plant the botanical species between 20 to 30 days before starting the purification system so there’s time for biological adaptation of the plants to the new environment. 

Considering phyto purification

Phyto purification systems are economically efficient solutions. It is estimated that however the initial cost can be elevated (6.500 euros on the hybrid solution by Kevin Quendric, for example), these water treatment systems pay for themselves in about fifteen years time as they do not require electric energy nor maintenance by a qualified workforce. 

Unlike conventional purification systems, phyto purification can support insects, birds, amphibians, contributing to the local biodiversity. The lack of chemicals makes the system an environmentally-friendly option available for water treatment. 

In addition to environmental and economic upsides, planted filters can be a beautiful landscape project as it has an undeniable aesthetic value. A symbiotic relationship can emerge. The wastewater produced every day by humans is rich in nutrients valuable for certain plants of every shape and colour. 

[1] Dias, Richardsson Mendes. (2019) Eficiência da Fitodepuração como Alternativa de Tratamento de Águas Residuárias: Um Estudo de Caso. Teresina:  IFPI

[2]https://www.build-green.fr/phytoepuration-creer-un-filtre-plante/doing_wp_cron=1617567011.8170158863067626953125, accessed 4 April, 2021.

[3] Ibidem

[4] https://wiki.lowtechlab.org/wiki/Phyto%C3%A9puration_eaux_us%C3%A9es, accessed 5 April, 2021.

[5] https://www.lenntech.com/phytodepuration.htm, accessed 5 April, 2021.

[6] http://www.graia.eu/en/our-activities/phytodepuration-and-lagooning/, accessed 5 April, 2021.

[7]https://www.build-green.fr/phytoepuration-creer-un-filtre-plante/?doing_wp_cron=161756 7011.8170158863067626953125, accessed 6 April, 2021.

[8] Ibidem

[9]https://www.researchgate.net/publication/326352770_Manual_de_sistemas_de_Wetlands_construidas_para_o_tratamento_de_esgotos_sanitario_implantacao_operacao_e_manutencao, accessed 6 April, 2021.

[10] Ibidem

[11] Ibidem

[12]https://www.build-green.fr/phytoepuration-creer-un-filtre-plante/?doing_wp_cron=1617567011.8170158863067626953125 , accessed 8 April, 2021.

[13]https://www.researchgate.net/publication/326352770_Manual_de_sistemas_de_Wetlands_construidas_para_o_tratamento_de_esgotos_sanitario_implantacao_operacao_e_manutencao, accessed 8 April, 2021.

[14] https://wiki.lowtechlab.org/wiki/Phyto%C3%A9puration_eaux_us%C3%A9es, accessed 8 April, 2021.

[15] Ibidem

[16]https://www.sciencedirect.com/topics/earth-and-planetary-sciences/water-purification-plant, accessed 9 April, 2021.

[17]https://www.build-green.fr/phytoepuration-creer-un-filtre-plante/?doing_wp_cron=1617567011.8170158863067626953125, accessed 9 April, 2021.

[18] https://www.sciencedirect.com/topics/earth-and-planetary-sciences/water-purification-plant, , accessed 11 April, 2021.

[19https://wiki.lowtechlab.org/wiki/Phyto%C3%A9puration_eaux_us%C3%A9es, accessed 11 April, 2021.

[20] Ibidem 

[21] https://www.researchgate.net/publication/326352770_Manual_de_sistemas_de_Wetlands_construidas_para_o_tratamento_de_esgotos_sanitario_implantacao_operacao_e_manutencao, accessed 11 April, 2021.

The post Phytodepuration with Degre.47 first appeared on Critical Concrete.
Did you miss our previous article…
https://www.thevisualconcretegroup.com/?p=296

post

Knowing Our Food: Scraps

Picture the last food scrap you threw away. Maybe you were dumping some potato peels in the trash, or composting the outer leaves of a cauliflower. Why did you throw it away? Was it for aesthetic reasons? Did you consider any of that food inedible? Did you have patience in that moment to think of a reason to keep it? Were you out of containers to store it in? There are a multitude of reasons why food ends up in the bin, but we hope this article can make it easier to give your food (waste) another chance.

Food waste, as we’ve explored in this series on food knowledge, is one of the most urgent yet avoidable contributors to climate change. Even a single apple that goes to waste due to poor storage strategies or aesthetic imperfections represents a loss of all its embodied energy. That is to say, all the water and land used to grow it, all the energy used to transport and store it, and all of the caloric energy it could have provided to someone are squandered. At such a small scale, it’s negligible, and yet when everyone believes that throwing away food is not a big deal, it leads to enormous quantities of waste that often end up in landfills, releasing methane (a potent greenhouse gas) into the atmosphere.

Reframing Fruit Scraps

One way to reduce food waste is to rethink what you consider food. Of course, this isn’t to say that you should go around eating nut shells and parts of food that leave you with indigestion, but some foods that we are taught to discard have great flavors and health benefits. 

On the most basic level, this applies to fruits with soft peels. Your apple, pear, peach, or nectarine skins can and should be eaten, but certain dessert recipes ask you to peel them, and in those cases, you can enjoy the peel by itself or use it in tea. Beyond those four, kiwi skin adds fiber and flavor when you eat it with the rest of the fruit, and dried pomegranate and hazelnut skin can be pulverized and added to smoothies or sprinkled on meals as a supplement. But fruit scraps don’t just have to be healthy; we highly recommend making treats out of your lemon and orange rinds. Although candied citrus rinds are great dipped in chocolate or sprinkled on cakes, the ones we made were devoured before they could make it to those stages.

More unusually, banana skins make a wonderful meat substitute in some recipes, like tacos or lasagna. Watermelon rinds make good pickles, but they can also be candied by cooking them in sugar syrup. If you make your own milk alternatives at home, you can use the strained almond, oat, rice, or cashew pulp for baking by replacing some of the flour in a recipe with pulp. (Be aware that milk pulp as a flour replacement will have an effect on the moisture and gluten content, so it only works in small ratios of pulp to flour and doesn’t work for difficult pastries, like croissants.) Another unusual recipe we tried was jam made out of passion fruit rinds. By boiling the rinds, taking the skin off, and mashing them with sugar, we cooked a slightly floral and astringent spread that goes well with bread or scones.

Vegetable Scrap Recipes

It’s helpful to rethink how you treat the scraps from your vegetables, too. Make sure not to waste delicious broccoli stalks or beet greens, and definitely don’t throw out the peels of your root vegetables. When a recipe requires peeled potatoes, the peels make a crispy snack or garnish when baked with some oil. Carrot greens transform into a delicious pesto when blended with oil, garlic, sunflower seeds, and salt.

Anything hard to chew can be blended into sauces, as is the case with kale stems and pea shells, and the stems of chard can be pickled. You can even sauté the tough green ends of leeks! The leaves of cauliflower, broccoli or romanesco broccoli should be cooked and eaten as well. Fava pods can be eaten whole, by grilling or sautéing them. When we tried out this recipe, we topped the pods with lemon juice, salt, chili flakes, and mint. 

It should go without mentioning that any vegetable scraps can be made into broth. Herb stems are superb for this purpose, but celery, onions, leeks, carrots, potatoes, and celery root all provide scraps to flavor your broth. Sometimes, there isn’t enough waste to produce broth, so these scraps can be stored in the freezer while you collect enough.

Similarly to broth, parts of some foods can be added to teas or infused on their own. This is most true for leaves, especially artichoke, persimmon, and strawberry leaves, and for dried or fresh citrus rind. 

Other Food Scrap Uses

Food scraps have purposes beyond just culinary! When making a vinegar-based cleaning solution for your house, lemon, orange and grapefruit rinds add a nice aroma. Banana skins serve as aphid repellents when they are chopped up and buried a couple inches deep around the base of a plant, and have anti-inflammatory properties when used on irritated skin. Coffee grounds and oat, almond and rice milk pulp are great body exfoliants, with rice and oat pulp having additional soothing properties when used on facial skin.

Many food scraps can be used to regrow foods, and these experiments double as educational projects as well. Root vegetables can be regrown by placing the tops of the root in water until new leaves begin to grow, at which point they can be planted in soil. Ginger pieces the size of an inch can be planted directly, and in very little time they will grow more ginger. Long, green vegetables such as celery, lemongrass, leeks, and green onions can be regrown by placing one inch of the bottom part of the plant (not counting the length of the roots) in a tray or glass of water until it begins to grow again. They can then be planted in soil. Leafy vegetables such as lettuce or endives undergo a similar process: the bottom parts are placed in water for several days or a few weeks until there is new growth and they can be moved to soil.

Scrap Dyes

We’ve saved the most exciting use for last: dyes! Many fruit and vegetable skins have tannins that help dyes bond well to natural fibers like cotton, linen, wool, or silk. The most well-known dyes made from food scraps are onion skins and avocado pits and skins. Yellow onion skins make yellow and orange dyes, red onion skins create colors between light lilac and deep magenta, and avocado scraps make a pink dye.

These dyes can be made stronger with alum powder, a mordant which helps dyes adhere to fabric better, but they can be used without it as well because of the presence of tannins in these food scraps. Some natural dyes, like the brown colors from chestnut and walnut shells, are vastly improved with the use of a mordant. Pomegranate rinds make a yellow dye and the leaves from loquat trees make a pink dye, both of which work best using a mordant.

Scraps in the Big Picture

Sometimes the scraps from your food just can’t be eaten or used, and that’s okay! When you get to this point, what’s most important is diverting your food waste from the landfill. If your city has a municipal composting program, you may have curbside compost pickup which is an easy way to reduce the emissions of your food waste, but you can also easily set up a compost in your own backyard, or get a small vermicomposting bin for your kitchen. Food waste can also be used to feed a biodigester, which produces biogas that you can use for energy. Both composts and biodigesters are part of our ongoing research at our production center, so you can expect an article soon about the merits and challenges of these systems in an urban setting. And lastly, if you do not have access to municipal or domestic compost where you live, you can see if any farmer’s markets or local gardens collect compost, and bring your food waste to them on a weekly basis. 

When it comes to food, there are so many systemic and cultural barriers to consuming it mindfully and avoiding waste. Overcoming preconceptions about food scraps that are seen as non-food is one part of working against these entrenched cultural beliefs that promote excessive waste. The problem, like any environmental issue, does not come down to just personal choices, but when these small changes are implemented at a wide scale, they can have significant effects, not just in the amount of food that goes to waste, but towards treating the food we have with respect. When we stop taking food for granted, we respect the seasonality of our produce, and stop letting vegetables go bad due to poor storage. You can read about these two related practices in the previous articles of our Knowing Our Food trilogy, and learn about how to preserve food for long or short periods.

The post Knowing Our Food: Scraps first appeared on Critical Concrete.

post

Knowing our Food: Preservation

If you are interested in our kimchi making process, click here to skip to the section about kimchi directly.

Do you ever stop to think about how you’re able to enjoy fresh strawberries, blueberries, and peaches in Winter? Contemporary food systems make an enormous variety of food available at any time of year. Produce travels long distances to be sold where it isn’t in season, undermining the business of small farms and emitting greenhouse gases. Local foods are riper at harvest because of shorter travel times, and choosing to buy local also supports the local economy. But even while shopping local, unseasonal food can be harmful to the environment; energy-intensive food production methods like greenhouses can produce 3-10 times the emissions as imported foods.[1]

Understanding why our food goes bad and what accelerates its decay helps reduce food waste, but fridges are only good at storing fresh produce for relatively short periods. There is a wide range of alternatives to fridge storage that keep fruits and vegetables from rotting for months or even years. This article will detail some long-term storage methods and their benefits depending on region and culinary purposes, and we will take you through our process of fermenting cabbage for kimchi.

When you decide to cut down the carbon emissions of your food, the produce available to you changes seasonally. The good news is that there are ways to store these foods for long periods so that you can still eat and cook with foods after their peak seasons. Alternatives to refrigerating food have existed throughout history, but the availability and convenience of the fridge has brought some of these practices out of the mainstream.

The two categories of traditional, low-tech food preservation are storing food in containers that control temperature and humidity, or preparing food to slow down its decay. 

Storage Methods for Food Preservation

It is important to note that food storage differs in summer and winter because different variables cause food decay in each season. Traditional food storage containers address the needs of produce through passive strategies that make use of the climate.


Zeer Pot

In hot and dry climates, natural fridges make use of evaporative cooling on the outer surface of a clay pot. In this method known as the Zeer Pot, water evaporation converts sensible heat to latent heat. This means that energy is released when liquid water is converted to vapor, reducing the temperature inside the container. The method uses two clay pots, one inside of the other. Between the pots is a layer of sand into which water is poured to begin the evaporative cooling process. Evaporation is continuous, ensuring that the natural fridge stays cool all day, but it relies on an outside temperature hot and dry enough to cause evaporation. Because the Zeer Pot serves the function of a fridge, it does not extend the life of food or preserve it any longer than a fridge, but it is necessary to mention when discussing how to store food without refrigerators or freezers. 


Root clamp using upcycled container

In cool climates and during the Winter months, some vegetables can stay fresh for longer by taking advantage of a steady temperature underground. Root vegetables can avoid frost by being buried, as ground temperatures fluctuate significantly less per day and can stay warmer than the winter air temperature.

Burying vegetables (and some fruits) can be done through covering the planted vegetables with soil or straw, or through harvesting the vegetables and putting them in small underground holes called clamps or silos.[2] Underground food cellars, when available, serve the same purpose. Given that a majority of the world population lives in urban areas, the first option is not as accessible, as it relies on growing your own food in large quantities. The last option, an underground root cellar, is useful for larger quantities of foods and can also be used to extend the shelf life of more than just fruits and vegetables.


Root Cellar

The most accessible of the three ways of burying vegetables is the “clamp” or pits that are completely or partially buried. These can be built relatively quickly using very little garden space and can upcycle used household items (such as washers or steamers). Proper care must be taken to ventilate to avoid mold and to protect the food from rodents or other pests. For protection against rodents, the trench can be lined with rust-resistant metal mesh, which simultaneously aids ventilation. Another method to strengthen ventilation is to place a bundle of twigs in the center of the pit to act as an air shaft. The old drums of washing machines are perforated, which makes them perfect pest protection, but bricks can also be used for the walls and ground of the pit as well. To protect against rain, a plastic sheet can be used to cover the pit, although there may be a problem if the soil around the vegetables becomes extremely saturated from heavy rainfall. 


Root Clamp

Sand storage is helpful to use in tandem with other cold storage methods because it regulates moisture conditions. It can be done at multiple scales, so in large boxes in a root cellar, in a root clamp or food pit, or even at the bottom of your fridge drawer, and it works with all root vegetables, onions, leeks, shallots, and cauliflower.[3] Sand storage entails pouring sand into a container and then submerging the vegetables completely.[4] The sand serves the purpose of a humidity regulator, removing excess moisture, so vegetables cannot be washed before they are stored in this way.[5] Sand storage requires that there be space for ventilation between the vegetables being stored, and the sand container should stay out of heated rooms or areas that are below freezing.[6] If you do not have a food pit, cellar, or food clamp, you can use this method on its own if you have a cold enough garage or, as mentioned above, in the bottom of your fridge drawer.[7]

Preservation Through Food Preparation

Drying


Drying food using a dehydrator, an oven, and the sun

Drying is a method best used for fruit, mushrooms and herbs. It is more easily done during summer because there is more heat and more fruit available to dry, but in the winter, citrus and fungi can be dried in the oven which helps heat the house. Vegetables can also be dried, but they should be blanched, or boiled quickly, before drying, which removes some healthy enzymes.[8] Dried foods retain most of their vitamins, except vitamin C, which degrades quickly.

Foods can be dried in the sun, in an oven, or in a dehydrator, making sure to allow sufficient space for ventilation. The process of drying takes several hours, but it is very hands-off, as most of the work involved is preparing the food by slicing it and putting it on drying trays. When using the oven, care should be taken to set a low enough temperature to avoid burning. Dried fruit is a delicious snack and can be added to baked goods for its flavor and texture. Mushrooms and herbs are multipurpose when dried, and just like dried herbs, mushrooms can be ground to produce a delicious seasoning powder for any meal.

Fermenting

Fermented foods preserve well because the acidic environment blocks bacteria from multiplying. Lactic fermentation is the process in which lactic microbial organisms convert sugars into lactic acid, creating an acidic environment that inhibits bacterial growth.[9] It is best known for making sauerkraut and other cabbage dishes, like kimchi and Salvadorian curtido. Usually the process is to cut vegetables, season them, and leave them in their own juices to ferment for a few days or a few weeks. Then, jars are stored in a cool place—either in a cellar or fridge—and last a year or more. At room temperature, sauerkraut lasts up to a few months,[10] but kimchi will only last about a week if left out.[11] Lactic fermentation allows more raw vegetables to be eaten throughout the year without relying on food travelling long distances. When eaten uncooked, fermented foods preserve their enzyme and vitamin content while adding healthy probiotics.[12] Fermentation adds acidity and a distinct fermented flavor.[13]

Canning and Salting

Canning relies on heat to kill both bacteria and enzymes.[14] Canned food is prepared by placing food in sterilized jars, then boiling the closed jars of food for several minutes to stop factors that cause decay, so the food stays edible almost indefinitely.[15] Canning is an easy process that is helpful for storing foods that will be cooked anyway. However, if we relied on canning to preserve all our food, we would miss out on beneficial enzymes and vitamins.

Salting protects food from the multiplication of bacteria because salt draws the moisture out, creating an inhospitable environment.[16] Often, salted food is rinsed before it is used for cooking, which reduces the sodium but, unfortunately, removes some of the nutritional value from water-soluble vitamins.[17] To work around this disadvantage, salting is best used if the preserved food is intended to be cooked with a high amount of salt, such as in broth, or simply consumed in small quantities.[18]

Our Approach

Every method for storing food in the long-term has specific conditions for which it is ideal. At Critical Concrete, we implemented some of these strategies according to the conditions in Porto.

Local climate is a necessary component of food storage strategies. In the case of Zeer Pots, low humidity is essential to ensure evaporation. As Porto is relatively humid even in the summer, evaporative fridges are not appropriate for keeping food cool in this area. On the other hand, burying produce is optimal in a cool and dry climate.[19] It can even be effective in places that receive snow, as long as certain precautions are taken against moisture.[20] Food preparation for preservation often lasts six months or more. Fermented foods last longer when stored away from sunlight and direct heat, while dried foods need to be stored in a dry environment, such as in dry bags or jars.


Pouring water in the sand layer of our natural fridge to trigger evaporation

In the Summer of 2019 we attempted to build a natural fridge. However, the temperatures inside were not cold enough to store food; on the hottest day, the fridge was 17 degrees, and on cooler days the temperature inside was 13 at the lowest. This is quite logical given Porto’s humid climate, which resulted in less evaporation, and on the warmest day we recorded temperatures, it was only 21 degrees outside. Our unfortunate results emphasize the need for attention to specific climate in storage methods for food preservation.

Kimchi

To look into food preparation methods for long-term storage, we attempted lactic fermentation, using a recipe for vegan kimchi available on the blog Maangchi.com.

We compressed it into the jars to avoid air bubbles. After 5 days fermenting at room temperature, we placed the delicious kimchi in the fridge. (Normally, fermentation at room temperature only occurs for 1-2 days, but we stored it in a very cold unheated room.)

In these before and after images, we can see the evidence of fermentation: there are dozens of air bubbles where, prior to fermentation, we could only see a few. The difference in hue is only due to the artificial lighting used in the first image, however the cabbage is slightly more translucent after fermentation.

Our kimchi turned out wonderfully, but we noticed a few things in the process of making it. First is that it is not shelf stable, relying on the refrigerator to extend the lifetime past a week. (When we build a cool cellar in the Critical Concrete kitchen, the kimchi can be moved there to limit reliance on the fridge.) Secondly, when getting the cabbage ready to ferment, we noticed that the wider jar made it easier (than two other small jars we filled) to pack kimchi without allowing bubbles. Third of all, though slightly minor, is that when preparing kimchi, it is necessary to soak cabbage in brine and then rinse several times to remove the salt. This has the same caveat as preserving food with salt: losing water-soluble nutrients from rinsing. That being said, kimchi makes up for any lost nutrients in probiotics and flavor, and can last more than a year when stored correctly.

Conclusion

When used in the relatively humid summers of Porto, the Zeer Pot technique offered little relief from the hot outside temperatures. In drier climates, it could be a simple and low tech way to expand cold storage or, even better when possible, reduce the need for a fridge. During the winter, burying food is a great way to extend the life of vegetables, although, as mentioned, the reality of urban living makes it difficult to accomplish in many homes. If it is an option, there are many traditional ways to go about it, but each one needs to carefully protect against moisture, cold, and pests.

How to store food outside of the fridge

Salting and canning are two simple methods of food preservation that are perfect for certain dishes, but both affect the nutrient content of food significantly. Dried food offers a wide variety of purposes: in baked goods, as snacks, or as seasoning. As most homes have an oven, it is quite accessible. During the summer it is more energy efficient, but, on the other hand, can help heat your home in winter. The process of fermenting requires very little energy expenditure and can be used for a wide variety of produce, but it is especially suited for vegetables. In fact, as drying can be better for fruits and fungi, and fermenting is great for vegetables, these two methods of preservation complement each other. Although fermentation alters the flavor of raw foods, this can be a benefit. In the case of our homemade kimchi, fermentation was a success. However, it failed to reduce our reliance on the fridge, while still posing some of the problems of salt-preserved food.

Our food culture is built around having every variety of food available constantly, without inspiring consumers to consider where and how that food is produced. There are often significant challenges to eating local, seasonal food, and, at the same time, it won’t solve the world’s problems to only eat such food. However, eating seasonal food when possible leads to more delicious, nutritious meals and helps the environment simultaneously. 

Stay tuned for our next food article in the series, on the use of food scraps.

Sources

[1] Ritchie, Hannah. “You Want to Reduce the Carbon Footprint of Your Food? Focus on What You Eat, Not Whether Your Food Is Local.” Our World in Data, Global Change Data Lab, 24 Jan. 2020, ourworldindata.org/food-choice-vs-eating-local. 

[2] Preserving Food without Freezing or Canning: Traditional Techniques Using Salt, Oil, Sugar, Alcohol, Vinegar, Drying, Cold Storage, and Lactic Fermentation. Chelsea Green Pub., 2007. 

[3] https://www.gardeningknowhow.com/edible/vegetables/vgen/storing-root-crops-in-sand.htm#:~:text=Root%20veggies%20that%20grow%20vertically,to%20entombing%20them%20in%20sand. accessed 18 February, 2021.

[4] https://www.gardeningknowhow.com/edible/vegetables/vgen/storing-root-crops-in-sand.htm#:~:text=Root%20veggies%20that%20grow%20vertically,to%20entombing%20them%20in%20sand. accessed 18 February, 2021.

[5] https://www.gardeningknowhow.com/edible/vegetables/vgen/storing-root-crops-in-sand.htm#:~:text=Root%20veggies%20that%20grow%20vertically,to%20entombing%20them%20in%20sand. accessed 18 February, 2021.

[6] https://www.gardeningknowhow.com/edible/vegetables/vgen/storing-root-crops-in-sand.htm#:~:text=Root%20veggies%20that%20grow%20vertically,to%20entombing%20them%20in%20sand. accessed 18 February, 2021.

[7] https://www.gardeningknowhow.com/edible/vegetables/vgen/storing-root-crops-in-sand.htm#:~:text=Root%20veggies%20that%20grow%20vertically,to%20entombing%20them%20in%20sand. accessed 18 February, 2021.

[8] Preserving Food without Freezing or Canning: Traditional Techniques Using Salt, Oil, Sugar, Alcohol, Vinegar, Drying, Cold Storage, and Lactic Fermentation. Chelsea Green Pub., 2007. 

[9] Preserving Food without Freezing or Canning: Traditional Techniques Using Salt, Oil, Sugar, Alcohol, Vinegar, Drying, Cold Storage, and Lactic Fermentation. Chelsea Green Pub., 2007. 

[10] https://growyourpantry.com/blogs/fermenting-pickling-preserving/how-long-does-sauerkraut-last, accessed 18/01/21.

[11] https://www.healthline.com/nutrition/does-kimchi-go-bad#shelf-life, accessed 18/01/21.

[12]Preserving Food without Freezing or Canning: Traditional Techniques Using Salt, Oil, Sugar, Alcohol, Vinegar, Drying, Cold Storage, and Lactic Fermentation. Chelsea Green Pub., 2007. 

[13] Preserving Food without Freezing or Canning: Traditional Techniques Using Salt, Oil, Sugar, Alcohol, Vinegar, Drying, Cold Storage, and Lactic Fermentation. Chelsea Green Pub., 2007. 

[14] Seymour, John. The Self-Sufficient Gardener: A Complete Guide to Growing and Preserving All Your Own Food. Dolphin, 1980. 

[15] Seymour, John. The Self-Sufficient Gardener: A Complete Guide to Growing and Preserving All Your Own Food. Dolphin, 1980. 

[16] Preserving Food without Freezing or Canning: Traditional Techniques Using Salt, Oil, Sugar, Alcohol, Vinegar, Drying, Cold Storage, and Lactic Fermentation. Chelsea Green Pub., 2007. 

[17] Preserving Food without Freezing or Canning: Traditional Techniques Using Salt, Oil, Sugar, Alcohol, Vinegar, Drying, Cold Storage, and Lactic Fermentation. Chelsea Green Pub., 2007. 

[18] Preserving Food without Freezing or Canning: Traditional Techniques Using Salt, Oil, Sugar, Alcohol, Vinegar, Drying, Cold Storage, and Lactic Fermentation. Chelsea Green Pub., 2007. 

[19] Preserving Food without Freezing or Canning: Traditional Techniques Using Salt, Oil, Sugar, Alcohol, Vinegar, Drying, Cold Storage, and Lactic Fermentation. Chelsea Green Pub., 2007. 

[20] Preserving Food without Freezing or Canning: Traditional Techniques Using Salt, Oil, Sugar, Alcohol, Vinegar, Drying, Cold Storage, and Lactic Fermentation. Chelsea Green Pub., 2007. 

The post Knowing our Food: Preservation first appeared on Critical Concrete.