- Cider is an alcoholic beverage prepared from apple juice.
- It has been produced for over 2000 years and is now made almost everywhere that apples (Malus pumila) are grown.
- In the UK, for example, the annual production is over 4.5 million litres.
- The cider making process is very similar to wine production and results in products that range from sweet to very dry, usually containing 2–8% (v/v) alcohol.
- Traditional cider is often uncarbonated and may not be clarified. Some may be served as naturally conditioned cask cider, analogous to cask-conditioned ale.
- However, most ciders are clear and sterile filtered or flash pasteurized products.
- They are artificially carbonated and analogous to bottled and keg beer.
- In France, carbonation may be achieved via the Charmat process. This technique, also used to produce some sparkling wines, involves a bulk secondary fermentation under pressure.
Apple Juice Extraction
- The making of cider is starting with the choosing of apples usually specific cider varieties that contain high levels of phenolic compounds.
- Single apple cultivars can be used, but more often cider is prepared from blends.
- The cleaned fruit is coarsely milled and the resulting apple pulp is pressed to extract the juice using either a large cylindrical press or a continuous belt press.
- Pressed pomace, consisting of skin, pips and core, can be used for cattle feed or pectin may be extracted for use in jam and confectionery manufacture.
- Freshly juice can be fermented immediately, or concentrated up to eight fold and stored for later fermentation, following pasteurization and pectin removal.
- Care has to be taken in the production of concentrate as furfurals (sugar degradation product) may be formed, which could impede subsequent fermentation.
Composition of apple juice
- Apple juice composition varies depending upon the apple varieties used.
- Compared with brewer’s wort, it has a lower pH of 3.0–4.0, contains 6–8 times less soluble nitrogen, and mono and disaccharides are virtually the only sugars present (Table).
- A typical sugar composition is 75% fructose, 15% sucrose and 10% glucose, with only small quantities of other simple sugars, oligosaccharides and starch.
Apple juice composition
|Amino nitrogen (FAN)||10–110mg/L|
- Apple juice also contains soluble pectin, which consists of polymers of galacturonic acid esterified with methanol.
- The major acid is L(-) malic acid, along with variable quantities of the phenolic acids: quinic, chlorogenic, shikimic and ρ-coumarylquinic.
- Polyphenolic constituents are tannins, primarily epi-catechin, and dimeric and trimeric pro-anthocyanidin.
- Other minor components include ascorbic acid, minerals and esters such as ethyl-methyl butyrate.
- Traditional wooden fermentation casks are used without temperature control, whereas modern commercial vessels are usually temperature-controlled vessels of 2000–9000L capacity, constructed of lined concrete, lined mild steel or stainless steel.
- Fermenter depths in excess of 14.5 m, which produce hydrostatic pressures of 1.5 atm, have been shown to impair cider yeast performance.
- Fresh juice or reconstituted concentrate may be supplemented with fermentable sugars before fermentation.
- Cane sugar is the usual source of additional fermentables, without which alcohol levels rarely exceed 6.0% (v/v).
- Traditional fermentations are performed by indigenous yeasts that originate from the skins of the fruit, the environment and processing equipment. Normally, sound ripe apples have less than 500 yeast cells per gram of fruit.
- These are primarily Kloeckera apiculata, Aureobasidium pullulans and species of Rhodotorula, Torulopsis, Candida and Metschnikowia, whereas Saccharomyces species and other sporulating yeasts are rarely found.
- Acid-tolerant bacteria such as Gluconobacter species are usually present but lactic acid bacteria are rare.
- The traditional-type fermentations are usually performed at ambient temperature. They are slow to start, usually beginning within 1–2 days, and continue for several weeks.
- In modern commercial operations the juice is treated to remove microbial contaminants by high-speed centrifugation, sterile filtration or pasteurization.
- If the apple juice is heat-treated constituent pectinases are denatured. As a result, cider does not clear as pectins remain undegraded unless additional pectinases are added.
- Apple juice is commonly treated with SO2, which has both antioxidant and antimicrobial function.
- The quantity of SO2 required to prevent oxidative browning and control unwanted microorganisms is dependent upon the pH of the juice: the lower the pH, the less SO2 is required.
- In many countries the maximum legal limit for sulphur dioxide is around 200 mg/L, which adequately retards aerobic yeasts, and both lactic and acetic acid bacteria.
- The treated juice is fermented with an added starter culture of S. cerevisiae. These yeast preparations originate from cider fermentations or may be selected wine making strains.
- Lower soluble nitrogen levels, compared with brewer’s wort, lead to relatively slow fermentation rates, which is exacerbated by the lower concentrations of yeasts used for pitching.
- This is often 5–15 times lower than in beer production, starting at only 106 cells/ml, rising to 5 x 107 cells/ml by the end of the fermentation.
- Supplementing the juice with ammonium salts does not increase the fermentation rate, but makes its progress more predictable.
- These cider fermentations are normally performed at 20–25°C and last for 1–4 weeks.
- Ideally, the cider yeasts should exhibit the following properties:
- Rapid initiation of fermentation
- Resistance to SO2 and high ethanol concentrations
- Low requirement for growth factors
- Ability to complete attenuation by fermenting all sugars
- Suitable flocculation characteristics
- Development of a sound organoleptic profile
- Production of polygalacturonase to degrade soluble pectin.
- During the yeast fermentation there is a decrease in pH due primarily to the formation of L(-) malic acid by the yeast.
- Also, minor quantities of a range of other acids are produced, including gluconic, lactic and succinic acids, and mono, di and trigalacturonides, derived from the enzymic degradation of pectin.
- Higher alcohols are important organoleptic components, but their actual levels depend on the apple variety used, juice treatment, the yeast strain employed, and both the fermentation and storage conditions.
- Generally, low pH and low nitrogen levels result in ciders with increased higher alcohol levels, whereas use of clarified apple juice and sulphur dioxide produces lower concentrations.
- Towards the end of the fermentation, the yeasts release nitrogenous compounds into the cider, including amino acids and peptides, along with pantothenic acid, riboflavin and some phosphorus compounds.
- This release of nutrients is important for any subsequent bacterial malo-lactic fermentation.
- After the primary fermentation is completed, the yeast is allowed to settle to the bottom of the fermentation vessel.
- Cider is either racked (decanted from the sediment) or partially clarified by centrifugation before storage under an inert gas blanket for several months.
- Naturally carbonated cider is a relatively small proportion of the market and is produced by carrying out a secondary yeast fermentation.
- However, a more common secondary fermentation is malo-lactic fermentation which can sometimes occur earlier, during the primary yeast fermentation.
- It is performed by lactic acid bacteria, usually non-slimeforming strains of Leuconostoc mesenteroides, Lactobacillus collinoides and occasionally Pediococcus cerevisiae.
- In addition to the conversion of malic to lactic acid, thereby reducing acidity, it brings about the conversion of quinic acid to dihydroshikimic acid and generates other flavour compounds.
- At the end of maturation the cider can be blended with old and new ciders to moderate the flavour, thus maintaining a consistent flavour profile for the product.
- Those ciders produced with added sugar reach 9–11% (v/v) alcohol and may be diluted with water before further processing.
- Cider blends are normally clarified by centrifugation or filtration, followed by sterile filtration or flash pasteurization at 85°C for 20s.
- These products are artificially carbonated during packaging and to maintain stability, chemical preservatives may be added, e.g. SO2, sodium benzoate and potassium sorbate.
Reference and Sources