The addition of fruit can completely change the character of the beer. It introduces fresh acidity, natural aroma, colour and an extra layer of flavour. At the same time, sugars are introduced into the beer along with the juice, purée or concentrate, which can be utilised by the yeast.
If the process is not properly planned, refermentation may occur after bottling. This can result in excessive carbonation, a change in flavour, cloudiness, over-carbonation of the containers and, in extreme cases, damage to bottles or cans.
What is uncontrolled refermentation in fruit beers?
Uncontrolled refermentation is the resumption of yeast activity after the main fermentation process has finished, most commonly following the addition of raw materials containing fermentable sugars.
In the context of fruit beers, the source of such sugars may be fruit juice, pulp, purée or concentrate. Sucrose, glucose and fructose are readily utilised by most brewer’s yeasts. If active yeast cells remain in the finished beer, they may initiate further fermentation following the addition of fruit.
This process may begin whilst the beer is still in the tank, during maturation, or even after it has been bottled. A particularly risky situation arises when beer is bottled before it has reached the intended level of fermentation.
What are the causes of uncontrolled refermentation?
Sudden temperature spikes
A rise in temperature does not in itself create new sugars, but it can significantly accelerate yeast activity if there are still fermentable carbohydrates present in the beer.
Beer that has remained stable in a cold store may begin to develop carbonation rapidly after being moved to a warmer warehouse or during transport. Therefore, low temperature should not be regarded as the sole method of protecting the product. Cooling slows down yeast metabolism, but does not remove the yeast or, as a rule, deactivate it permanently.
Premature bottling
One of the most common causes of problems is bottling before fermentation is complete. A single measurement of the extract does not in itself confirm the beer’s stability. The result should be verified over the following days (at least 3 consecutive days), whilst maintaining a comparable sample temperature and using the same measurement method.
The sugars introduced with the fruit must also be taken into account. The mere completion of fermentation of the base beer does not mean that the product will be stable after the addition of the concentrate.
If fruit is added immediately before bottling, its impact on potential refermentation must be assessed during the pilot trials.
Hop creep
Hop creep primarily affects beers that are heavily cold-hopped. Enzymes present in the hops can break down some of the more complex carbohydrates into sugars, which then become available to the yeast.
In fruit beers, the risks can be cumulative. On the one hand, there are sugars derived from the fruit; on the other, there is additional fermentability caused by the hop enzymes. Therefore, in beers that combine dry hopping with fruit additions, the extract stability should be monitored particularly closely.
Equipment cleanliness
Refermentation is not always caused by the yeast used in primary fermentation. It may also be caused by wild yeast or bacteria that have entered the product via an inadequately cleaned tank, pipe, pump, valve or tap.
Some microorganisms are capable of utilising compounds that standard brewing strains do not ferment. As a result, the beer may appear stable for a while, before its flavour, aroma and carbonation levels begin to change.
Particular attention should be paid to areas that are difficult to clean: gaskets, connectors, sampling valves, filling heads and systems used for dosing fruit ingredients.
Proven methods for preventing secondary fermentation in fruit beers
Method 1: timing the addition of fruit
The simplest way to minimise the risk is to add the fruit early enough for the yeast to ferment the added sugars whilst the beer is still in the tank.
This approach works well when the aim is to produce a dry beer, and the brewer is prepared to accept a partial loss of the most volatile fruit notes. Intense fermentation can reduce the freshness of the aroma, so the timing of addition should be chosen according to the type of fruit and the desired product profile.
It is worth knowing the extract value of the raw material and its planned dosage. Good-quality fruit concentrates for beer should have consistent parameters, which makes it easier to calculate the amount of sugars going into each batch.
Method 2: confirming stability prior to bottling
Before bottling begins, it is essential to confirm that the final extract remains stable over time. Taking measurements two or three times on consecutive days provides far more information than a single result.
In breweries with the appropriate facilities, a fermentation test can be helpful. It allows an assessment of whether there are any compounds remaining in the beer that the yeast can still utilise.
Monitoring should not be limited solely to the extract. It is also worth observing the pressure, carbon dioxide level, pH, aroma and flavour of the sample, as well as its behaviour after storage at a higher temperature.
Method 3: selecting an effective stabilisation method
If the product is to retain some of its natural fruit sweetness, simply allowing fermentation to run to completion may not be sufficient. Depending on the plant’s capabilities, methods used include filtration to reduce the yeast cell count, pasteurisation, aseptic filling, or a combination of several process safeguards.
Each of these methods has different technical requirements and may affect the flavour. Excessive heat treatment may diminish the fresh fruit aroma, whilst insufficient filtration will not ensure stability if live cells remain in the product.
The method should be selected according to the type of beer, sugar content, expected shelf life and distribution conditions. Cold crash alone cannot be regarded as full microbiological stabilisation.
What else is worth remembering when trying to avoid secondary fermentation in beer?
The quality and consistency of the fruit raw material are of great importance. Before implementing a recipe, it is worth checking the extract, acidity, pH, sensory profile and behaviour of the concentrate when mixed with a specific base beer. A guide explaining which juice to choose for fruit beer may also be helpful.
The effect of fruit on colour and clarity must also be taken into account. Changes occurring during storage may result not only from fermentation, but also from oxidation, polyphenol reactions and the natural instability of pigments. Further information is provided in the article on how fruit concentrates affect the appearance of beer.
The finished fruit beer should be stored as cool as possible, but it is equally important to confirm its stability beforehand. A controlled process, accurate measurements and proper hygiene provide more effective protection than relying on low temperatures to keep the yeast dormant throughout the product’s shelf life.