1/23/18 Chapter 5 Cheese Cheese, Yogurt & Sour Cream Curdled and A durable form of processed milk! - 5 -10 times milk concentrate milk – using •Likely first prepared acids and from soured milk and as milk was stored in enzymes to stomach pouches make milk •Lactose (sugar) products allows this to happen as it serves as a source of food for microbes Curds and Whey The Process of Cheese Making • Curdling – separation of milkfat and protein from What was she whey o Acid, heat, enzyme eating? Coagulated (rennet) or combinations all cause curdling and separated milk! • Curd setting – finishing o pH, salt content, bacteria culture, cooking times • Ripening - aging – (react with oxygen) and allow molds and or other bacteria to alter fresh curd to hard aged cheese 1 1/23/18 Ingredients Types of Cheese Milk: Acid Coagulated Fresh Cheese (lactic acid from • Source influences the milk fat content, type of fats bacteria) (saturated), protein content and small organic molecules • no enzyme is used to finish the curd • Goat, Yak, Cow, Buffalo • Cottage and Cream Cheese • Animals with higher fat and protein create rich cheese Heat-Acid Precipitated Cheese (acid and heat • Goat have low casein – less curds and more crumbly finished cheese precipitate/coagulate the protein and cause milk fat to • Feed, Time of year and lactation curdle) • Alter protein / fat ratio and small flavored molecules • Add low amounts of acid to 75-100oC temp milk • Lowest fat in August, highest in October • High moisture and protein • Homogenization disrupts the size and membrane coverage of fat globules – casein binds to fat and doesn’t • Ricotta (Italy) Channa and Paneer (India) curd as well Types of Cheese Ingredients Semi-hard Washed Cheese (washing cheese removes Milk: acid and lactose) • Source influences the milk fat content, type of fats • Acid and enzyme induced curdling (saturated), protein content and small organic molecules • But removal of milk sugar and acid results in no • Goat, Yak, Cow, Buffalo fermentation results in a moist and less finished cheese • Animals with higher fat and protein create rich cheese • Gouda, colby, muenster, mozzarella … • Goat have low casein – less curds and more crumbly finished cheese Hard Cheese (Low and High Temp) • Feed, Time of year and lactation • Low moister makes a more dense hard cheese • Alter protein / fat ratio and small flavored molecules • Lowest fat in August, highest in October • Elevated temps and pressing drive off water • Cheddar, Romano, Parmesan, Swiss • Homogenization disrupts the size and membrane coverage of fat globules – casein binds to fat and doesn’t curd as well 2 1/23/18 Casein – key for cheese Milk Proteins and Sub micelles are Fat Globules held together by phosphorylated casein – calcium ion interactions - k-casein caps the growing micelle, binds water and repels interactions with other casein micelles Metabolism – Curd Formation lactic acid production Acidifying milk, increasing temperature and action of rennet lead to curd formation. i.e. disruption of casein micelles… Fermentation is a - acid formation (adding acid – acetic or citric) or production of way for bacteria to lactic acid from metabolizing bacteria limit protein interaction replace limited amounts of NAD+ Loss of charged glutamates and • Lactate is side aspartic acids product diminishes ability of casein to bind to • Typically used calcium and for aged neutral charged k- cheeses casein stop repulsion and form weak aggregated precipitates (curd) 3 1/23/18 Enzyme catalyzed Different types of bacteria curd formation Lactobacteria use lactose for Rennet – protease that fermentation. hydrolyses the protein backbone Used as “starter” culture to • Along with acid further begin fermentation degrades proteins in casein micelles and globules • Both mesophillic (moderate • Found in 4th stomach of milk- temp) and thermophilic fed calf (heat tolerating) lactobacilli strains • Also found in some fruits – pineapple, kiwi or papaya (why • Neither can tolerate more don’t you make jello using than moderate acidic these fresh fruits?) conditions • Vegetable rennet is from thistle • If cooking curds A second “finishing/non- • Most commercial cheeses use thermophilic cultures are starter/ripening” bacteria is used to a cloned / engineered rennet needed produce more acid and produce called chymosin • This first step is called new flavor producing compounds “ripening” Rennet attacks kappa-casein Temperature curd formation The negative tail of If using culture, higher temps k-casein is cleaved increase by specific fermentation rates recognition by making more acid. rennet - Proteins denature at higher temps - Forms stronger - Combination of curds than acid only acid, rennet and precipitation heat make for tight curds. 4 1/23/18 Next step – Removing Moisture Drying the cheese curd Gravity – through mold and Fresh cheeses drained – used for soft cheeses (camembert…) retain moisture and Cutting curd – smaller the dryer, sugars creates a more firm cheese due to increased surface area/mass ratio Aged pressed Heating and stirring curds continues denaturation of proteins cheeses are to release water from curd - exposed hydrophobic protein amino Temps impact final dryness of cheese pressed to dry and acid side groups will not interact with - Cheddar 100oF water reducing “holding” capacity - Gruyere 120oF have less lactose - Activates bacteria and enzymes for - Parmesan 130oF more acid and creation of new flavor compounds Final Steps Brining the Cheese Curds from the whey Osmosis – removal of water from the cheese - net movement of dissolved Cheddaring – stacked and particles from a region of high restacked at warm temps concentration to a lower to encourage increased concentration acid production Water and salt move in Pressing – squeeze curds opposite directions in a high together and remove salt brine water for hard, aged - water is removed from cheese by salt brine and salt cheeses is driven into cheese Higher salt inhibits pathogenic bacteria growth and alters enzyme function to create flavor compounds 5 1/23/18 Aging – (Ripening or Chemistry of ripening Affinage) Enzymes breakdown fat, protein and carbohydrates to new flavor compounds Aging is the process of allowing starter and finishing bacteria and their enzymes to alter composition of fresh cheese • The French term for ripening is affinage , which means ‘end’ or ‘ultimate point’. As such, at times this stage of cheese making is carried out by an affineur, a cheese tenderer or finisher. • The affineur takes care of the cheeses in the cheese-ripening cellars until the cheese has ripened adequately for packing and sale Cheese Flavoring Macromolecules and flavor Protein, fat and metabolites (know this word!) Proteins (casein & whey) degrade to amino acids • Proteins – mostly degredation products of casein - Glycine and alanine are sweet, Tryptophan is bitter • Amines – the amino portion of amino acids - Cysteine is eggy, Glutamate is MSG – savory flavor enhancing - Some amino acids are further metabolized to ammonia, putrecine and • Fish smell – trimethylamine trimethylamine • Putrescine – polymer of amines The more finished • Sulfur – from cysteine- amino acid side group the more flavors – • Ammonia – nitrogen from amino acids why? Fats are highly modified • Amino acids themselves have tastes • lipases release fatty acids altering acid and sharpness • Fats – different sized and modified fatty acids add • Fatty acids are further oxidized to ketones, alcohols or lactones different flavors and textures – molds typically alter fats • Produces buttery (diacetyl) taste, grassy and other flavors • Short chain fatty acids – buttery or peppery taste • Smaller break down products – ketones – highly fragrant 6 1/23/18 Finishing Microbes Finishing Microbes Holy Cheese (cow)? – Propionibacteria: Smear Bacteria – smelly cheeses like munster and • Convert lactic acid to propionoic and acetic acid plus acetic limburger cheese acid and CO2. Also other flavors • Live in high salt (most bacteria won’t do well) • Grow on surface of cheese – need oxygen and can’t grow in • Used to make Swiss Cheese acidic conditions from starter culture • Need higher temps and time for bacteria to grow and produce • The cultures are swiped or smeared • Growth requirements reflect on surface of pressed cheeses • Responsible for protein breakdown origins of bacteria Propionoic acid into… stinky molecules animal skin Sulfur containing compounds – methanethiol And methylthioacetate Lactic acid + Acetic acid Carbon Dioxide (g) Finishing Microbes Mold actively modifies fats Moldy Cheese producing short modified fatty acids • Microbes which grow in dry oxygenated conditions, tend to age cheese from inside out. • Likely introduced to cheeses as young cheeses were stored in P. Camemberti - Lactic acid is moldy caves for storage further degraded by surface smear – higher pH results in • Penicillium roqueforti and P. camemberti most common strains precipitation of calcium • Produce color, texture and flavor phosphates of casein forming a hard shell and produces • Metabolize fat and proteins differently than yeast or bacteria lactones, ketones and sulfur • Blue (bleu) Cheese – streaked or even injected with mold from fats and proteins spores – give blue, grey or green color – often a favorite with wine and cheese 7 1/23/18 Blue Cheeses – Based on Cheddar cheese Origen Aged cheddar flavor comes from production of savory amino acids and aromatic byproducts of fats, sugar and protein metabolism • During aging enzymes released by starter and Cambreles-