1. Overview Cider is an alcoholic drink that is fermented from fruit juice. Fermentation is most commonly carried out using yeast whereby yeast could be deliberately added or present naturally in the fruit. Uncommonly, cider production could also be done through malolactic fermentation which is the conversion of malic acid to lactic acid and carbon dioxide. In this webpage review of articles, both fermentations of cider will be discussed. This review is written by Chua Niying, currently a biotechnology student at Murdoch University, taking Industrial Bioprocessing and Bioremediation module.

2. Background Paper 1 : Cabranes, Morenoe, & Mangas, J. (1990). Dynamics of yeast populations during cider fermentation in the asturian region of spain. APPLIED AND ENVIRONMENTAL MICROBIOLOGY, 56, 3881-3884. Cider production was most commonly done using yeast fermentation, Saccharomyces cerevisiae was mostly found in this study. There was a usage of two types of apple mixtures in different fermenting systems. The different systems affected the yeast populations and hence affecting the quality of the cider. Paper 2: Arthurs & Lloyd (1999). Kinetics, stereospecificity, and expression of the malolactic enzyme. APPLIED AND ENVIRONMENTAL MICROBIOLOGY, 65 (8), 3360-3363. Malolactic fermentation could be used for the production of cider and it was carried out by a lactic acid bacteria and malolactic enzyme. Alcoholic fermentation was also included to convert sugar in the fruits to alcohol as sugars could interfere with the secondary fermentation. Outcome for this fermentation resulted in a production of characteristic flavor and aroma of cider.

3. First paper Dynamics of yeast populations during cider fermentation in the asturian region of spain by Cabranes,et al. The aim of this study was to investigate effect on yeast population caused by the difference system and initial apple mixtures used for cider yeast fermentations. Alternative system (enzymatic keeving) and traditional system (spontaneous keeving and enzymatic keeving) of producing cider through yeast fermentation was compared in terms of the amount of yeast microflora in the barrels that was collected from the different systems. During cider fermentation, it was found that different types of yeast are presents in both types of system but Saccharomyces cerevisiae was predominantly found in both system of fermentation and in both apple mixtures as well. Proving that Saccharomyces cerevisiae is mainly involve in fermentation for an apple cider drink.

4. Second paper Kinetics, stereospecificity, and expression of the malolactic enzyme by Arthurs & Lloyd In order to make cider, alcoholic fermentation need to be done with saccharomyces sp. for the removal of sugars like glucose, sucrose and fructose in the apple and covert them into alcohol. It was found that the conversion of sugars to alcohol was necessary as it could affect the result of malolactic fermentation (MLF). An enzyme called malolactic enzyme need to be present hence the fermentation system need to be primed for malolactic enzyme for MLF to work successfully. MLF could be affected by changes in pH, different expressions of isomers of malic acids and presence of sugars in growth medium. Theses factors contributed to the flavor and aroma of cider drink.

5. Comparison First paperSecond paper Similarities o Apple cider production o Methods of fermentations o Involves Saccharomyces yeast species. o Focuses on how different changes in the production process, materials and conditions can affect the fermentation procedures. Differences o Focus mainly on the amount of yeast can affect fermentation. o Making use of apple mixtures for yeast fermentation o Focus on cell growth for the lactic acid bacteria which produces the enzyme for malolactic fermentation o Study makes use of pure apple for the alcoholic fermentation and then malolactic fermentation.

6. Comments Not much recent studies are done on cider making, most probably most of the facts were already established in the 90s. Even though it seems like cider making it just all about fermentations, there is a lot more to look into in making a good, enjoyable apple cider. Maybe other fruit ciders could be made through the same methods. More researches would be needed by studying on how to treat the fruits and different conditions needed before any fermentation take place. Thank you.

7. References Gunningham., P. (2003, June 07). Cider making. Retrieved from http://homepage.ntlworld.com/scrumpy/cider/cider.htm Cabranes, Morenoe, & Mangas, J. (1990). Dynamics of yeast populations during cider fermentation in the asturian region of spain. APPLIED AND ENVIRONMENTAL MICROBIOLOGY, 56, 3881-3884. Arthurs & Lloyd (1999). Kinetics, stereospecificity, and expression of the malolactic enzyme. APPLIED AND ENVIRONMENTAL MICROBIOLOGY, 65 (8), 3360- 3363.