Q: What aspect of manufacture or composition is it that causes the distinctive holes to form in cheeses like Gruy猫re, Leerdammer and Emmenthal?
A: The holes or eyes in such cheeses are actually bubbles formed as the cheese matures.
The starter bacteria used in Swiss-style cheesemaking contain lactose-fermenting organisms such as Lactococcus cremoris, lactobacilli and lacrate-fermenting propionibacteria. These propionibacteria metabolise the lactate which is produced by the other organisms into propionate, acetate and carbon dioxide.
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The gas expands, forming bubbles within the protein matrix of the cheese. Presumably the bacteria are clustered together so that the gas is produced in small pockets.
Cheese is a viscoelastic material that is able to flow under quite small stresses. The lactate production peaks about 20 days after the manufacture of the cheese. The propionibacteria are therefore active when the curd is quite plastic and deformable. The structure of the curd is thus critical in determining the quality of eye formation in the cheese.
If the curd is quite smooth and cohesive, nice round bubbles will form whose size depends on the amount of carbon dioxide that is present and also the plasticity of the curd. If the curd is grainy or layered, poor quality slits will be formed instead of the holes usually seen in the finished shop product.
A: While working in the Austrian Alps I was lucky enough to witness the traditional Emmenthal-type cheesemaking technique. Apparently much of the annual production is wasted each year because of faulty holes. In order to avoid this there is a lot of competition by Alpine farmers to secure the services of the best cheesemakers they can find; a cheesemaker with a record of fine hole production is a valuable commodity in the region.
The process itself has many stages and each affects the production of the holes and their different properties (frequency, morphology and minimum and maximum sizes) to various degrees. Because of the large number of variables and the difficulty in judging them, cheesemaking is perhaps best left as an art rather than a science.
First, the quality of the cheese (fat/protein/water ratio) will affect the curd/whey ratio when the rennin is added. The time they are given to react is also crucial in determining the coherency and texture of the whey. Once the curds are removed they are compressed into a mould after being salted and having certain strains of bacteria incorporated.
The degree of compression into the mould will also affect the development of the holes. For example, too firm a compression results in small but much more frequent bubbles, whereas too soft a compression results in large bubbles that can burst through the surface.
In addition, the curd grain size and texture affect the morphology of these holes. A finer grain size combined with hard packing can result in a fine microhole structure, while too large a grain size results in long bubbles rather than the required round ones.
The amount of salt that is added before compression also affects the depth of the rind and the hardness of the cheese. The incorporation of foreign bacteria can also devastate the hole structure.
In addition to all of the above factors the time the cheese is allowed to mature is crucial, as is the correct temperature of the maturing room. Maturing cheeses are often removed from the maturing room, turned and scrubbed with salt to assist the development of the hole structure.