This article is to record the artisan and modern methods of making washed curd type cheeses such as Gouda & Edam, it is divided into the following sections:
- Curd Making
- Curd Washing
- Curd Fusion / Knitting
- Air Drying
Washed curd type cheeses are named for their making process of removing whey and adding water to wash the curds, other names are stirred-curd and soaked curd type cheeses. The original washed curd semi-hard type aged cheeses are Gouda and Edam originating in Netherlands, others examples being Havarti, Colby, Fontina, Danbo and Jarlsberg. They are typically commercially made in 4-14 kg wheels (Gouda) or 1-2 spheres (Edam) or blocks and are characterised by a limited number of regularly distributed small 2-10 mm diameter round eyes. They have a smooth texture when young (4 weeks) to medium matured, are easily sliced and have good melting properties. When older they develop more caramel flavor and amino acid crystals.
Washed curd cheeses are historically made from cow’s milk using mesophilic mixed-strain starters cultures which are rennet coagulated to form a curd. After curd formation, the curd is cut and then undergoes a mild low temperature scalding to control the moisture content and then part of the whey is removed and warm water added to “wash” the curds which removes some of the lactic acid to create a sweeter cheese. The washed cut curds are then pre-pressed in the warm whey and then pressed out of the whey to form wheels. After pressing they are brine-salted to halt acidification and then historically aged unwaxed. The texture is mainly influenced by its moisture content, fat content, pH and age.
Traditionally raw whole cow’s milk was and is still used in farmhouse for example Goudse boerenkaas (farmhouse Gouda in Dutch). Current commercial making is with pasteurised partly skimmed milk for regulatory health reasons and to provide lower fat cheeses as preferred by some consumers.
Lactic acid producing mesophilic mixed-strain starter cultures are added to the milk, the type influences the intensity of aroma and flavor. Commonly these contain Leuconostoc and Lactococcus lactis as they generally lead to fuller aroma and some CO2 production. Sometimes starter cultures containing Propionic acid bacteria are used for eye growth such as in very open textured Jarlsberg & Maasdam cheeses. Acidification occurs once starter culture is added, the rate of acidification during manufacture is a key influence on the cheese texture.
Other common additives are annatto for colouration and CaCl2 if using pasteurized milk, also sometimes herbs or spices are added, the most common being cumin.
Traditionally pre-acidification of the milk is not performed and calf’s rennet is added directly after the starter to coagulate the milk into curd.
After curd formation, the curds are cut and after resting for a few minutes gently stirred as the cut curds are fragile.
Once a sufficient amount of whey is released, curd washing occurs by removing whey equivalent to 25-30% of the original milk volume, adding a similar volume of hot water bringing the curds up to a mild scalding (<36C as above normally harms mesophilic cultures), and then stirring more vigorously for ~30 minutes to wash the curds and avoid curd fusion. The hot wash water should be added carefully over the whole vat to avoid any local overheating. This washing provides two effects, the dilution of the whey reduces the lactose content of the curds and thereby controls the amount of lactic acid created and thus the final pH of the cheese. In addition the mild scalding enhances syneresis reducing the water content of the curd. During washing stirring is intensified which also aids syneresis.
Traditionally after washing the curd was allowed to settle to a flat uniform layer in the bottom of the vat and then left for some time resulting in partial fusion or knitting of the cut washed curds. This process can be accelerated by lightly pressing the curds in the whey either in a mold in small cheese making or in current commercial making by placing perforated (to allow whey escape) stainless steel plate weights on the curds in the whey.
In traditional farmhouse making, when the curds have become sufficiently fused, they were cut into blocks, the blocks wrapped in cloth and placed in wooden wheel shaped molds and pressed for several hours at pressures increasing to 0.5-1 bar / 50-101 kPa / 7-15 psi to obtain a very thick and tough rind. During pressing whey leaks from the block of curds until the surface is closed and a thin firm rind forms which inhibits further moisture loss until brining. After pressing the cheese wheel was removed from the cloth, any extruded rind between the follower cut off and the cheese turned and left in the mold for several hours to shape into a more symmetrical Gouda cheese wheel or Edam shaped sphere and to enable allow acid production in the cheese to continue so that the remaining lactose is almost completely converted into lactic acid when brining started, about 24 hours after renneting (modern manufacturing methods have shortened this time).
Modern manufacture uses faster growing starter cultures and plastic molds with nets or finely perforated steel molds and uses lower pressures and shorter pressing times. Also, the pressed and molded cheese is placed in brine within 1 hour after pressing. The more efficient molds negate the need to trim off extrusions or to turn the cheese and the faster starter cultures negate the need to leave the cheese in the mold for several hours.
pH of the pressed cheese at 4 hours after renneting should be about 5.7.
Washed curd type cheeses are normally initially have high water content after pressing and thus are quite fragile and deform under their own weight. Thus rather than direct dry salting they are bathed in cold brine which results in uptake of salt into the surface of cheese, dehydration of the surface which becomes white, harder and more brittle resulting in a stronger less fragile cheese for subsequent handling. Additionally, the salt and cold both inhibit the growth of the lactic acid producing bacteria, at least at the surface and provide the normal roles in cheese making of being a preservative and contributing to flavor. Even after brining it takes considerable time for the NaCl to diffuse into the core of the cheese, for example ~8 weeks for a large commercial 10-12 kg wheel.
Brining time can be up to 7 days for large commercial cheeses.
After brining pH should be 5.2. Typical Gouda cheese at 14 days ripening has a ~4.2% salt-in-moisture content rising to 5.7% in older cheeses.
After brining the cheese surface are air dried at room temperature, during which the cheese is handled carefully as the dried rind is under tension and the cheese can easily split.
Traditionally when the cheese is free from visible moisture it was coated with regular rubbings of the rind with a dry cloth and unboiled edible linseed oil (flax seed oil) and stored for 4 weeks to several years at 12-15C and a relative humidity of 85-88%. Linseed oil has the special ability to polymerize/harden into a solid form providing a strong coat reducing water evaporation and surface molds. Aging at 17C or above results in the milkfat being liquid and the fat exuding from the cheese (sweating). During aging the cheeses are turned regularly to ensure even development and shape.
Commercial washed curd cheese are after brining and air drying coated with a copolymer plastic dispersion (normally containing natamycin to inhibit the growth of moulds and yeasts) that after sufficient drying and repeated treatment provides the cheese with a smooth, somewhat shiny moisture and gas impermeable coating which hinders the growth of microorganisms on the cheese surface.
During the first two weeks of aging the young cheese requires air movement to dry sufficiently and will normally lose an additional 2-3% by weight (depending on the size of the cheese) after which weight loss diminishes. After 4 weeks ripening, optimal moisture-in-non-fat-solids is ~58% and pH should be ~5.30 (Edam is lower ~4.9).
After a minimum 25 days of ripening, historically a wax coating (yellow or white for Gouda, red or black for Edam) was applied to Gouda-type cheese to protect the cheese during transport against microbial growth and weight loss due to moisture evaporation. General practice used to be to wash and dry the often unclean cheese surface before waxing. Waxed cheeses were wrapped in a foil for better presentation and packed in cardboard boxes for storage and shipping. Storage, especially for young cheeses, was normally below 10C to maintain their shape and avoid bulging which could damage the wax layer. Shipping to and storage in warmer countries was normally for older and harder cheeses.
Current commercial manufacture with better ripening controlled rooms plastic coating normally does not clean the cheese before waxing.
If a cheese is to be waxed, the ripening cheese should be kept under good drying conditions and good maintenance in order to prevent any visible microbial activity and to develop a clean, shining and closed surface. The pH of the cheese surface should be well below 6.0, its moisture content should be low and the salt concentration should be high enough to offer sufficient preservation before a cheese can be waxed. Failure to do so before waxing can result in molds and gas under wax causing off textures, aromas, and flavors.