Nutrient Deprivation: Keeving

Keeving is a process that seeks to remove nutrients needed for fermentation in order to create residual sweetness. Yeast need nutrients and vitamins to ferment and while they are good at finding or creating many of these nutrients, it only takes the loss of one to stop the process. Keeving is a process that removes some of these nutrients, with the goal to slow and ultimately stop the fermentation process. If you’ve read a book on wine and often cider making, one of the things that is discussed is the desire to have a strong fermenting yeast so it will complete fermentation, which uses all the available sugar. For me, this objective always seemed wrong for cider. The goal should be to create a balanced product. Something not too sweet, acidic, or bitter. Reading about keeving and the concept of removing yeast nutrients in order to stall fermentation and leave residual sweetness spoke to me. It nudged me down the dark path of challenging conventional thinking related to the hard cider making process. It made sense to me that if you have a highly acidic base with low sugars, relative to grape wine, and therefore, low alcohol content, having a way to create residual sweetness would be key. It led to me questioning why we add nutrients to cider and why we use Saccharomyces cerevisiae yeast strains when inoculating. For me, keeving, which has been a common practice in France and England for hundreds of years or more, was a sign from the past screaming for the attention of modern cider makers.

I don’t just mean that we should all be making keeved cider. I have never actually keeved or even tried to keeve a cider. What I mean is that our ancestors used keeving as a tool to solve a balance problem for cider. We have figured out that adding pectin methyl esterase (PME) and calcium chloride to a cider that we can more consistently create a keeve but you don’t have to add those compounds to keeve a cider. Also, adding them doesn’t guarantee you will create a keeved cider. The pH, the temperature of the fermentation, the aggressiveness of the yeasts, and the various other compounds naturally in your juice all impact the ability to create a keeved cider. However, the concept of nutrient deprivation as a means of controlling fermentation and ultimately, residual sugar content is the real goal. Keeving is just one example of how even our ancestors wanted to make balanced ciders and sought methods to control their fermentation. This concept is what has been pushing me to find more ways to naturally create balanced ciders. In some ways, this website, my book, and my passion to understand cider can all be linked back to keeving. I will probably never actually attempt to make a keeved cider but, I won’t stop seeking ways to make balanced ciders. That’s what I made when I created Sweet Orange last year, which has some natural residual sweetness.

Sweet Orange Cider Label: A color and sweetness experiment.
Sweet Orange Cider Label: A color and sweetness experiment.

So what is keeving? In the paper by F.W. Beech and S.W. Challinor about the keeving process(1), they actually differentiate keeving from defecation. They define defecation as the process where the compounds like PME and calcium chloride are added and keeving being the natural process that creates the same condition without the additions of the compounds. Besides the word defecation being off-putting, I am going to define this process as keeving since the outcome is the same and the addition of compounds only increases the chance of creating a keeve. Ultimately, the goal is to create a cider that has some level of residual sweetness because of nutrient deprivation. I realize that some keeved cider has effervescence but i could make a still or carbonated cider that is keeved. Keeving is a type of nutrient deprivation. Let’s explore how it works.

Keeving uses the pectin naturally found in the apple or pear to form a gelatinous mass. The pectin is created through enzymatic reactions, this is why the PME is added, and the pectin is pushed to the top of the fermenter by the CO2 created during the fermentation process. The pectin masses pick up other compounds and even yeast and as it reaches the top of the fermenter, it forms what is often called a brown cap or in French, chapeau brun. It’s brown because it traps the tannins and other phenolic compounds as well as many of the nutrients used by yeast to ferment. This includes nitrogen sources that the yeast need to effectively consume the sugars. The result is that you have an extremely clear band of cider between a sediment layer at the bottom and a brown gelatinous mass on top. Racking the clear cider in the middle from between these two layers will give you a cider that is low in nutrients and yeast.

This clear cider is just starting to ferment so the current %ABV is low and there is still a good amount of sugar remaining in the cider. If you didn’t remove the clear cider from the fermenter, it would normally continue to ferment. This fermentation generally becomes more aggressive as the yeast biomass increases, which will break up the gelatinous cap on top. This frees the trapped yeast and nutrients, which further increases the level of fermentation. The result will generally be a cider that is dry (has no residual sugar). This brings into perspective the reasons why certain recommendations are made when trying to create a keeved hard cider.

  • Temperature: It is recommended to ferment cool for keeved ciders. Temperature impacts the fermentation rate with cooler temperatures naturally making the fermentation slower and less aggressive. One of you main tasks is to catch the keeved cider once the gelatinous cap has formed and before it breaks up. A cooled ferment will slow that process and increase your chance of catching it. However, I have seen caps form and cider clear on warm ferments. They just dont last very long.
  • Apple Variety: You want apples that have a significant amount of pectin. The pectin helps form the cap and trap the yeast and nutrients. Using varieties with higher level of pectin will help create the cap and extract the yeast and nutrients.
  • Apple Nutrients: Since the goal is nutrient deprivation, you definitely don’t want to add any nutrients to your juice and ideally, you will use apples that are naturally low in nutrients. This can be related to the apple variety but much more linked to the orchard practices. An orchard that is commercially maintained, meaning it is irrigated and fertilized, will have more nutrients in the apples. The age of the orchard can also have an impact. As orchards age, they draw more and more nutrients from the surrounding soil. If this isn’t replenished, these older orchards will have less nutrients. Using apples from old, unmanaged, and wild trees are preferred because your nutrient level is already low.
  • Apple Ripeness: Generally, the riper the apple, the less nutrients and the more pectin you will have. Again, the goal is to reduce the nutrients and the plan is to use pectin to help do that so ripe fruit supports that process.
  • Maceration of the Pulp: Maceration of the apple pulp after milling and before pressing is another tool to help release the pectin from the apples so it can form the cap. Apple varieties naturally rich in PME will help this process or you can augment this by adding PME.
  • Calcium: Calcium in the juice combines with the pectic that is released from the PME to form the gelatinous mass that forms the cap. The addition of calcium through salts or chalk is used to help ensure the mass is formed. The gelatinous cap helps to ensure yeast and nutrients are trapped in it.

For a detailed description of the process, I have included the keeving instruction sheet from Cider Supply, which used to be included when acquiring PME from them for keeving. Unfortunately, they are no longer offering the PME enzyme but gave me permission to share these instructions to support the industry(2).

So keeving has been used for many years as a way of naturally creating a sweet cider. This ancient process that I have never attempted is what set me asking all sorts of questions. Should cider be dry or should it be balanced? If it’s okay to keeve a cider in order to naturally create residual sweetness, why isn’t it okay to use other processes and adjustments to do the same thing? Is PME really the key or will other pectin creating enzymes create the same result? Is the calcium addition the key? If we want a slower fermentation, what about juice clarification? Why does the industry push the use of Saccharomyces cerevisiae yeast if other non-Saccharomyces yeasts offered slower more controlled fermentations and more natural residual sweetness from glycerol? My questions keep going and I don’t see them stopping. So, if you enjoy, you have the keeving process to thank for it. It was the impetus for its creation and my quest to understand cider.

(1) F.W. Beech and S.W. Challinor, Maceration and defecation in cider-making, 1950’s

(2) C. Rylands, Renaissance Orchards a company of Cider Supply, LLC

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