The Role of Acids in Soft Drink Production

Acids play a crucial role in soft drink manufacturing, contributing both to flavor enhancement and product preservation. Among the most commonly used are phosphoric acid, citric acid, and malic acid. These organic and inorganic acids are essential ingredients in achieving the distinct taste profiles and shelf stability of modern beverages.

Phosphoric acid, widely used in cola-flavored drinks, imparts a sharp, tangy taste that balances the high sugar content. It also serves a preservative function, inhibiting microbial growth in the sugary medium. However, its widespread use has sparked health concerns in recent years, as excessive consumption may be linked to lower bone mineral density and kidney issues. As a result, some manufacturers are gradually reducing its concentration or replacing it with milder alternatives.

Citric acid, naturally found in citrus fruits, is favored in lemon-lime and fruit-flavored sodas for its refreshing, citrusy taste. It not only enhances flavor but also acts as a chelating agent, binding metals that could otherwise catalyze spoilage reactions. Malic acid, derived from apples, offers a more persistent tartness and is often used in conjunction with citric acid to produce a more rounded flavor, especially in apple, grape, or berry-flavored drinks.

These acids are introduced during the ingredient preparation stage, carefully blended with sweeteners, flavorings, and preservatives. Precision is critical—acid concentration must be optimized to ensure flavor consistency, product safety, and regulatory compliance. After mixing, the acidified syrup is diluted with water and carbonated by injecting carbon dioxide under high pressure, giving soft drinks their characteristic effervescence.

Advancements in beverage technology now allow for better acid control and flavor modulation using pH sensors and automated dosing systems. Quality control remains a top priority, with every batch undergoing rigorous testing for taste, acidity, carbonation levels, and microbial safety before packaging.

In essence, soft drink manufacturing is a meticulous fusion of chemistry, food science, and engineering. Acids, though used in small quantities, are indispensable in delivering the crisp taste, vibrant aroma, and long shelf life that consumers expect from their favorite fizzy drinks.
The Role of Acids in Soft Drink Production

Carbonation process of beverages

Carbon dioxide is a colorless, odorless, and incombustible gas that’s one of the most abundant gasses present in the atmosphere. It exists in solid, liquid, or gaseous states and is used in many chemical processes, including for refrigeration and cooling.

The process of carbonation involves either injecting the gas into a stream of water or product or adding it to the static liquid in a pressurized vessel.

The liquid is chilled and cascaded down in an enclosure containing carbon dioxide (either as dry ice or a liquid) under pressure.

Increasing pressure and lowering temperature maximize gas absorption. Product is usually filled at a cool temperature to minimize the loss of CO2 during the process and transit to the capper. Carbonated beverages do not require pasteurization. The dissolution of CO2 in a liquid, gives rise to effervescence or fizz.

When CO2 dissolves in H2O, water and gaseous carbon dioxide react to form a dilute solution of carbonic acid (H2CO3). The chemical reaction for this process is: H2O + CO2 ⇋ H2CO3

The units for measuring the amount of dissolved CO2 are commonly stated as grams of CO2 per liter of beverage (g/L) or as volumes of CO2 (STP) per volume of liquid (vol/vol).

Carbonation process produces the characteristics fizziness and bubbling in these drinks and this is due to the dissolved CO2 in a liquid under pressure. The carbonation process also changes the taste of the water and gives it that delicious bite that many of people love. This bite is caused by the acid when the carbon dioxide dissolves in the water and then reacts with it forming carbonic acid.
Carbonation process of beverages

Soft drinks bottling process

Soft drinks rank as America's favorite beverage segment, representing 25% of the total beverage market. Soft drinks include all drinks made from water or mineral water, sugar, aromas, and essences, and usually contain carbon dioxide.

The first step in the production of soft drinks is the syrup preparation. The syrup is a sugar and water solution, in which sugar or glucose can be used, while diet drinks are prepared using sweeteners or a combination of sugar and sweeteners.

The dissolved sugar and flavor concentrates are pumped into the dosing station in a predetermined sequence according to their compatibility. The ingredients are conveyed into batch tanks where they are carefully mixed; too much agitation can cause unwanted aeration. Conventional soft drinks contain 90 percent water, while diet soft drinks may contain up to 99% water.

The syrup may be sterilized while in the tanks, using ultraviolet radiation or flash pasteurization, which involves quickly heating and cooling the mixture. Fruit based syrups generally must be pasteurized.

Carbon dioxide (CO2) is added to soft drinks during the bottling process to give the drink its fizz. Carbon dioxide adds that special sparkle and bite to the beverage and also acts as a mild preservative. The solubility of carbon dioxide gas in water depends on the pressure and the temperature of the water. The colder the water, the higher the solubility. In order for carbonation (absorption of carbon dioxide to occur, soft drinks are cooled using large, ammonia-based refrigeration systems.

The carbonation of soft drinks varies from 1.5 to 5 g/L. Carbon dioxide is supplied to soft drinks manufacturers either in solid form (as dry ice) or in liquid form maintained under high pressure in heavy steel containers.

The finished product is transferred into bottles or cans at extremely high flow rates. Empty bottles and cans are transported automatically to the filling machine via bulk material handling equipment. The containers are immediately sealed with pressure-resistant closures, either tinplate or steel crowns with corrugated edges, twist offs, or pull tabs.

Because soft drinks are generally cooled during the manufacturing process, they must be brought to room temperature before labeling to prevent condensation from ruining the labels. This is usually achieved by spraying the containers with warm water and drying them.

Filling are all performed almost entirely by automatic machinery. Returnable bottles are washed in hot alkaline solutions for a minimum of five minutes and then rinsed thoroughly. Single-use containers are usually air- or water-rinsed before filling.

The majority of soft drinks are filled under pressure into bottles (glass or PET) or cans, achieving a maximum CO2-content of 8 grams. After filling, the bottles are immediately closed off with a (sterile) crown cap or a cap with plastic layer.

After the filling process, the soft drinks are sent to the distributor, who can repack the drinks in smaller quantities or deal directly to the final customers.
Soft drinks bottling process

Use of Intense Sweeteners in Soft Drinks

Use of sweeteners in soft drinks is not restricted to low calorie or dietetic products. In some countries, particularly where sugar price are comparatively high, intense sweeteners are used in combination with sugar or glucose syrups to give more efficient formulations. 

Intense sweeteners provide sweetness, the amount supplied – i.e. the relative sweetness of all intense sweetness – will depend on application. Intense sweeteners do not supply the mouth feel of sugar and in some cases, they may supply undesirable side tastes or prove to be incompatible with some flavors. For these reasons, use of intense sweeteners in soft drinks is rarely a case of direct substation of sucrose in the regular product formulations; more often than not, total reformulation is necessary. 

It may be necessary to adjust the acidity and use buffers to assist stability of some sweeteners. Some adjustment of flavor system used is commonly required and the use of gums or small amounts of sugars can improve mouth feel and control fobbing during filling. 

Use of ingredients that mask undesirable side tastes may also be required. Increasing the carbonation of low calorie products may also help mask undesirable side tastes and give the illusion of better mouth feel. 

Sweetness synergy occurs with many combinations of intense (and bulk) sweeteners. The effects can be twofold: a higher perceived sweetness than would be expected from the theoretical sum of the relative sweetness values of the individual used and in some cases, a marked improvement in taste quality of sweetness that have undesirable side tastes. 

The optimum sweetener system will vary depending on the product and will not necessarily be a sweetener blend. However if a sweetener blend is to be used , useful starting point often quoted for blends of two intense sweeteners is that sweeteners are used in an inverse ratio to their relative sweetness (to each other), so that each sweetener contributes 50% of the total sweetness. 

Use of Intense Sweeteners in Soft Drinks

Organic removal in Soft Drinks Processing

Dealkalisation is not the only ion-exchange process that is currently finding a place within the soft drinks industry. The coagulation process not only reduced the alkalinity content of the water but also removed the organic matter as part of the flocculation reactions. 

The dealkalisation process, however, is specific to the removal of alkalinity from water and all other constituents in the feed water will remain unaffected. Organic matter in the raw water may cause taste and odor problems in the carbonated product, particularly after sterilization using chlorine. 

In some areas the naturally occurring organic matter reaches levels where it is likely to give color to the water, which will necessitate its removal to meet the required specifications. Other waters may also contain significant concentrations of organic matter (colorless to the naked eye) which will depend upon the nature and type of the organic molecule as well as the concentration. In these circumstances organic removal must be considered a necessity. 

Removal of organic matter by ion exchange was developed in the 1960s as a method of protecting anion exchange resins in a demineralization plant in order to maintain the quality of treated water produced. The process uses an organic scavenger resin operating in the chlorine form. Natural organic matters are complex organic molecules that contain carboxylic acid active groups, meaning that they will act as weak anions, and will be held on the organic scavenger. 

The organic scavenger is a highly porous resin that will allow the organic molecules easy passage in and out of the structure. Ion exchange resins with a macroporous or macroreticular structure are particularly suited to this application and offer physical strength coupled with capacity and reversibility of organics during regeneration. 

As ion-exchange treatment will only remove about 70% of the organic matter of the residual organic concentration after scavenger treatment is high enough to cause problems with the final product. As a general rule waters having an organic content above 1ppm as measured by the 4 hours at 27 degree C permanganate test will require treatment while those waters that have a concentration at 1 ppm or below will not normally require special treatment. 

Regeneration will use 10% sodium chloride prepared from concentration brine, though under certain conditions regeneration will be made with a mixture of 10% sodium chloride hydroxide and 2% sodium hydroxide, which will give the scavenger an operating capacity. The regenerant will displace almost all of the organic matter absorbed in the previous operating cycle but some residue will remain in the resin and will require other regeneration techniques such as hot soaking or alkaline brine regeneration to assist in its removal. 

Under certain condition the residue will not ne removed by any means and this residue will be classed as irreversible fouling of the resin. The irreversible fouling of the resin will progressively increase and there will come a tome when the fouling threshold will reach such a level indicating that the economic life of the resin has been reach, which will mean that the resin must be changes. 

Alkaline brine regeneration tends to remove more of the absorbed organic matter from the resin and therefore the build up of irreversible fouling will be slower. 

Organic removal in Soft Drinks Processing