Swiss Cheese Defects

Swiss cheese (Emmental-style) defects fall into two broad categories: make (process) issues and microbiological contamination. Here is a full breakdown:

The Normal "Eye" - What Success Looks Like

In Emmental/Swiss-style cheese, round, smooth holes called eyes are formed intentionally by Propionibacterium freudenreichii, which produces CO2 during the warm room ripening stage. Ideal eyes are round, dime-sized, and evenly distributed. Any deviation from this is a defect.

Defect Categories

1. Eye / Hole Defects

Defect	Description	Cause
Blind cheese	No eyes form at all	Insufficient Propionibacterium activity; too-cold warm room; excess salt
Too many eyes	Overpopulation of holes	Excess Propionibacterium or contaminating gas-producing bacteria
Nesting	Eyes form very close together or "nest" within each other	Handling/stirring curd after pumping over from vat
Streubel	Many small, rough, curdy-looking eyes	Dumping loose curd on top of cheese, or air incorporated during pump-over (no predraw whey)
Blowholes	Large irregular gas pockets	Late-blowing by Clostridium spp.; problematic during slicing/packaging

2. Structural / Texture Defects

Defect	Description	Cause
Splits / Cracks	Elongated cracks instead of round eyes	Cold storage too warm (>39°F / >4°C); rough handling/slamming during turning; microbial spore contamination
Weak body	Soft, overly pliable texture	Excess moisture; culture imbalance; too-long warm room
Pasty/mealy body	Crumbly or grainy texture	Low pH at milling; too-dry curd

3. Microbiological Defects

Defect	Organism	Mechanism
Late blowing	Clostridium tyrobutyricum	Spore-forming anaerobe from raw milk; produces H2, CO2, and butyric acid weeks-months into ripening; causes irregular large holes and off-flavor
Early blowing	Coliforms (E. coli, etc.)	CO2 and H2 production in first days; indicates poor hygiene/sanitation
Discoloration	Serratia marcescens	Orange/red pigment on rind or cut surface

4. Flavor / Aroma Defects

Defect	Cause
Rancid / butyric off-flavor	Clostridium late blowing; lipolysis by contaminating bacteria
Bitter	Excessive proteolysis; excess chymosin; wrong starter culture balance
Gassy / fermented	Coliform or Clostridium contamination
Lack of characteristic nutty sweetness	Insufficient Propionibacterium activity

Root Causes Summary

As summarized by University of Wisconsin Center for Dairy Research, there are two fundamental root causes:

Make issues - problems in the cheesemaking process (temperature control, curd handling, salt levels, warm room conditions). These are easier to diagnose and fix.
Microbiological contaminants - unwanted bacteria (especially Clostridium spores) entering via raw milk or poor sanitation. These are harder to trace and control.

Prevention Strategies

Use high-quality, low-spore-count raw milk
Maintain strict hygiene and aseptic sampling at key control points
Control warm room temperature and duration precisely
Avoid disturbing curd after pump-over
Monitor starter culture balance regularly
Keep cold storage at or below 39°F (4°C) to prevent splits

The "Hay" Discovery (2015)

A landmark study by the Swiss agricultural institute Agroscope found that tiny bits of hay in traditionally collected milk act as nucleation points - structural weaknesses in the curd where CO2 accumulates and forms eyes. This explains why modern, hygienically collected milk (no open bucket/hay contact) produces fewer or smaller eyes. The traditional eye formation is therefore a combination of microbial gas production AND physical nucleation sites from hay particles.

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