Hot water immersion vs Cold water immersion


For every 4 tons of wheat or rice, 6 tons of straw is produced.

This by-product gets in some regions often just burned as it seems it has no value.

But as straw consists of cellulose, hemicellulose, and lignin and with a c:n ratio between 34-120:1, it is a perfect resource for cultivating mushrooms. By cultivating and selling them, additional income is provided.

But to grow mushrooms, the straw has to be prepared using various treatments.

But which treatment should you use if your budget is tight?

To answer this question, let us first talk about the reasons for using these treatments.

The first reason is to

  1. Eliminating competitor microorganisms or
  2. Reducing competitor microorganisms
  3. Extractive removal, hydrolysis of hemicellulose to produce sugars
  4. Break down of the lignin, which gives access to cellulose and hemicellulose and
  5. Heat will melt the natural waxy coating on straw materials.
    While the first two points focus on the competitor

microorganisms, the last three points provide nutrients for the mycelium.

Eliminating or at least reducing competitor microorganisms is crucial as these microorganisms inhibit the growth of the mycelium. While there are many competitor microorganisms, main once are:

  • Trichoderma, which consists of 200+ species
  • Penicillium, of which 300+ species are
  • Aspergillus with around 350 species.

To eliminate or reduce these competitors. different methods of disinfection were developed.

Pasteurization which reduces competitor organisms by utilizing steam or hot water, chemical or biological pasteurization.

Sterilization which eliminating all life-forms; heat (steam), chemicals, gas, UV radiation, pressure, or radioactivity), and

Composting which alters the chemical and bacterial composition of the substrate by self-heating and shifting the pH value and, therefore, reduces competitor organisms. Certain methods such as radioactivity or gas are not commonly used in mushroom cultivation. Therefore, we can classify them by grouping these methods into chemicals and non-chemical methods.

In the chemical group are several different compounds used, of which I will only mention one which is limestone as the other once are hazard compounds meaning the application of them will seriously harm you.

The non-chemical group consists of

  • Autoclaving which is steam sterilization with pressure and applied for 15 min … 4 hrs at 121°C.
  • Super pasteurization which is steam sterilization without pressure (atmospheric) and used for 12-48 hrs at 100°C.
  • Pasteurization for 2 … 6 hrs at 60-100°C.
  • Hot water immersion, which is used for 10 min … 96 hrs 55 … 90°C.
  • Boiling for ~ 30 min at 100°C and
  • Composting which takes place in two phases. Phase I 70°C for 4-5 days, and phase II 48°C for 2-3 days.

Suppose we rank these methods by their costs to use them.

We see that composting together with some pasteurization methods are the cheapest. On the other hand, due to its high temperature and pressure, autoclaving and super pasteurization, due to its long duration, can only run at a higher cost.

As we want to find the best methods for tight budgets, I will only focus on cold water immersion using limestone and hot water immersion. To understand the challenges using these two methods, we have to look at the growing conditions of the competitor microorganisms.

First up is the pH level.

  • Trichoderma can survive a pH level of 8.
  • Aspergillus withstands a pH of 12. 3.
  • While Penicillium even tolerates a pH of 14.

Using limestone increases the pH level to 9.5 and above.

If 6-14 kg per 100 liters is used.

Here, we already see why cold-water immersion will only reduce the competitor microorganisms as they tolerate even higher pH values.

It could be found that using limestone lead, to a contamination level, meaning the number of bags contaminated of around 5 %. In some cases even higher. If cold water immersion using limestone is applied, a biological efficiency of around 58 could be found.

But what about the temperature tolerance of the competitor microorganisms?

For the different types of Trichoderma harzianum species, it could be found that type Th1 and Th2 survive 60°C for 9h, while type Th4 even withstands 79°C for 17 hours.

The Aspergillus species Aspergillus Flavius survives 121°C for 30 min, whereas Aspergillus niger only 60°C for 1h.

Penicillium, on the other hand, withstands 70°C for 1 hour.

Here, we see that to eliminate or at least reduce most of the competitor microorganisms, a temperature greater than 80°C and a duration of 3+ hours should be applied. Using this method (80°C for 3 h), a contamination level of around 2 % could be reached. While achieving a biological efficiency of around 58-98.

More on using limestone to treat substrate can be found in the following video.

Talk to you there.


Growing Pleurotus: How much limestone should I use? 👇👇👇