February 28 2023

Chilleres in wine production

In one of my previous articles, an important issue relating to calculation of refrigeration needs during wine fermentation stage was raised, i.e.,

  • How much heat is released during red or white wine fermentation? And is there any difference?
  • What are cooling requirements for fermentation?


According to the physiological properties of yeast, it generates heat when fermenting. It means that each yeast cell consumes sugar and oxygen O2 and produces carbon dioxide CO2, alcohol and releases heat (yeast consumes and produces many more, but this article is focused on the main points). In classic process technology books of the last century a value of about 23.5 kcal from each gram-molecule of sugar is given as an amount of heat released. However, both kcal and gram-molecules are obsolete nowadays; only very few people (or no one at all, especially refrigeration engineers) use them today. For example, the task to find a chiller of the required capacity always faces the issue of the required cooling capacity, which is measured in kW, as well as the required temperature, measured in degrees Celsius (°C).

The temperature is more or less clear, and it can be reduced to the following basic levels:

Process White wine Red wine Optimal temperature range Benefits
Fermentation thermal control +++ +13…+20°С Aromatic enhancement in white wines.

Stopping fermentation.

Thermal control of fermentation and meccanization +++ +25…+30°С Reducing aroma losses.

These are recommended guidance values, because each winemaker, based on his own or others’ experiences, may choose to use a particular temperature, which can differ from the figures given in the table. But, in general, those temperatures will be close to the indicated ones.

But cooling capacity poses questions. Each winemaker needs to provide just as much cooling as the amount of heat energy released throughout the fermentation time that may ensure maintaining the stable fermentation temperature at the level set by a winemaker. It means that winemakers need a simple formula for calculating the refrigeration needs. In this article, a goal that I set for myself is to develop such a simple instruction for winemakers.

But, first of all, I want to note that a chiller, which will provide cooling services should be selected considering not only the needs of heat released during fermentation, but also heat gains, which will be additionally present, such as: heat from outdoor air and solar gains, heat losses from pipes and pipelines, processes running simultaneously with fermentation, etc. Therefore, please note that in this article I will analyze only a heat load from fermentation, and all the rest is omitted for the sake of simplicity.

Let’s return to the fermentation process. As previously mentioned, scientists measured the amount of heat released during alcoholic fermentation from one unit of sugar. For any winemaker, it is convenient to measure sugar content in % Brix, or in g/l. According to these values, the amount of heat should be given.

When analyzing information and data, which are accessible and freely available, it can be concluded that, on average, 1 gram of sugar releases about 0.56 kJ of heat by fermenting with yeast.

Therefore, if we have a must volume and an amount of sugar values at the beginning of the fermentation process, we can derive a formula to calculate the total amount of heat that should be released during the complete fermentation of sugar available in the existing must volume:

∑amount of heat = amount of heat released from 1 g of sugar* amount of sugar* must volume

Accordingly, if calculating using the formula, one can come to an understanding that, for example, with a starting sugar of 22% in 1 thousand liters of must about 34 kW of heat will be released, and in 10 thousand liters about 340 kW of heat will be released, respectively.

But it is necessary to pay special attention to the issue and explain that this capacity should in no case be used to choose a chiller, because this is the total amount of heat that will be generated during the entire fermentation process from the starting sugar value in the must to the so-called “dry” one. And since the fermentation process takes some time and also depends on various factors, the capacity per hour will be different.

Winemakers distinguish two main stages of fermentation: vigorous fermentation and quiet fermentation. Understanding that the largest share of heat to be generated during the vigorous fermentation is logical; therefore, to simplify the task, we will assume that we need to remove that total heat during the vigorous fermentation. Therefore, a winemaker, knowing the fermentation time, can also calculate the required chiller capacity. For example, if a vigorous fermentation takes 5 days, a cooling load will be about 0.3 kW, and if 10 days, it will be 0.15 kW, respectively.

Thus, this value is a necessary parameter for selecting a chiller.

But I draw your attention to the fact that it is just a mathematical model, and there are a lot of factors that can affect the actual use and change this value. For example, a portion of heat generated during the life processes of yeast is absorbed by carbon dioxide CO2 and alcohols and escapes from the must volume during fermentation. According to various documents, this value can be up to 10% of the total fermentation heat. So, for example, the capacity of the chiller can be reduced by this value.

But in any case, the given value of 0.56 kJ/g allows you to select a chiller with a safety margin chilling option and thereby protect a must from excessive heating during fermentation. But nevertheless, do not forget about complex calculation of all simultaneous needs for cooling, and only after this choose a chiller for your application. If this calculation is not possible, please contact qualified specialists or contact me directly.

In conclusion, I would like to add that besides cooling, there are cases when you need to heat a must during fermentation. For example, if the weather is very cold. So, with minimal changes in the lines a chiller available with a heat pump option (i.e., a chiller that has a water heater option) will also help, when warm water instead of cold water is to be supplied into the tank jacket. Thus, winemakers will be able to provide the required heating to maintain the desired fermentation temperature.

Can chillers produce simultaneously heating and cooling energies? Yes, it is possible, because from the technical point of view a chiller always generates both heat and cold at the same time. The question is whether such a chiller is provided with a water heater option, because most chillers remove heat into the air outside a manufacturing facility, and thus winemakers cannot use the heat.

So, please do not forget this and order a chiller with a set of options for your application.

In this article, I focused on calculating heat generated during fermentation because fermentation is one of the most powerful and longest processes, which require cooling. In addition, the article discusses chiller applications to provide cooling and heating services to winemakers. For more information, see our other articles or contact me directly for a consultation.