Being able to create a hard cider with some residual sweetness is often referred to as the holy grail of cider. The reason for this is because that sweetness can be used to balance the high acids often found in dessert apples and the tannins found in cider apples. This cider season I set about trying to develop ways to easily create hard cider with some natural residual sweetness. I had several approaches that I tried and while not statistically significant in sample sizes, I was able to test some theories and achieved some positive results. There are specific ways that you can ensure some residual sweetness, which I cover in my post on making hard cider sweet. However, the three ideas I explored this season where the following.
- Yeast Mutation
- Pressure Sterilization
- Cider Fortification
Yeast Mutation:
Yeast are interesting little organisms and by little, I mean microscopic. They are eukaryotes. They contain organelles that function like our human organs. They reproduce even more rapidly than rabbits. In a single fermentation, a yeast might reproduce or bud 3-6 times. However, this could be even higher depending on conditions. Each budding cycle creates an opportunity for the yeast to evolve or mutate. This is how many beer yeast have come to be. Because beer yeast is often harvested and used for a new batch, the process caused many strains to evolve to better meet their environment. Top cropping or bottom cropping and timing influence the environmental pressure placed on yeast and impact how it might evolve. You don’t find this situation as often in wine yeasts because they generally are not harvested and reused.
This year, I set about trying to evolve some yeast strains to better ferment cider and the pressure I placed on them was through bottom cropping before fermentation was complete. Yeast that fall to the bottom early will often die due to loss of nutrients as the layer of sediment and yeast build. They also flocculate more readily, which reduces their fermentation efficiency. For me, they are the perfect yeast to harvest if I want to try to create a yeast that are less likely to ferment all the sugar in a hard cider. That was the plan and I set about doing a primary racking when the gravity was between 1.010-1.015. This is where a Tilt can come in handy. I harvested and also plated these yeast so I could grow up another colony. I didn’t expect to have positive results in one season or maybe ever. However, yeast reuse, culturing, and exploration was an area I definitely wanted to learn more about.
I didn’t have any recognizable success on creating a cider that had noticeably more residual sugar but I did make some great tasting cider with the yeast I reused. I had some hard ciders that had a few points of residual sugars but I can’t attribute it to mutated yeast. I will continue to explore this concept and seek to evolve yeasts but I also have a new plan for next year. Instead of using Saccharomyces cersvisiae strains that have been used for years to ferment wine and have been evolved to ferment malt sugars in beer, I plan to start exploring non-Saccharomyces strains like Hanseniaspora uvarum and Pichia kluyveri. This is where I believe hard cider has been held back because of the lack of research in developing true cider yeasts. For example, some of the strains I have acquired do not ferment sucrose. Since apple juice doesn’t normally have complex sugars like malt in beer, having a yeast that won’t ferment sucrose may lead to a hard cider that has more residual sweetness. Expect more to come but here is a sneak peek at where I am heading next year with my yeast mutation and exploration path.
Pressure Sterilization:
Carbon dioxide (CO2) acts as a preservative(1) and not just from its ability to create a gaseous barrier that keeps out oxygen. Suspended CO2 also has some preservation actions. However, another aspect of CO2 is pressure. Pressure can be used to kill the micro flora in juice and hard cider(2). It does this by bursting the cell walls of yeast, mold, and bacteria. E. Juarez-Enriquez and associates used ultra high pressure pressure to achieve this in apple juice. However, other research indicates that yeast can be killed at a pressure of approximately 104 psi. However, lower pressures start to impact the ability of yeast to work.
I have experimented with this idea several times when making berry adjunct hard ciders like my Rock’n Raspberry hard cider. After fermentation, I add a small amount of berry juice to my cider and then immediately filter it with a 0.5 or lower micro filter. To help ensure it’s stable, I force carbonate it to a sparking level around 3.0-3.25 volumes CO2. For these experiments, I wanted to see if I could avoid the sterile filter and rely more on pressure. I did two batches of cider. These were ciders that I had racked with a specific gravity of 1.010-1.015 as part of my yeast mutation experiments.
In my first batch, I filtered the cider after racking using my in-line filter system (water filter style often used for beer) with a 5 micron nominal filter, not sterile. I then applied 60 psi of pressure in my keg, which are rated for 130 psi with a safety relief valve, and force carbonated it with my cider shake method. I wanted to see if a light filtration followed by moderate pressure would kill the yeast colony. I cold crashed it for one month at 40F and bottled it in champagne bottles. For this experiment, it worked. I have my Sweet Orange hard cider that has around 1.010 points of residual sugar.
For my second batch, I followed the same approach but I didn’t filter this one. I simply tried to use pressure to kill the yeast. Instead of filtering it first, I simply force carbonated it to 60 psi using my cider shake method and then cold crashed it. I bottled it again in champagne style bottles and monitored it. Initially, all seemed good but I started noticing a lees build up in my bottles. After a few months at room temperature, I had some very bubbly bottles of hard cider. This one was called Bubbles and it could be considered a Pét Nat cider. However, the level of carbonation exceeds pétillant. Actually, it exceeds reasonable and I don’t recommend going this high in carbonation. However, it is very tasty. I need to filter or try higher pressure to ensure I kill the yeast and create a stable hard cider. More work is needed, especially since my sample sizes were small but the results were interesting.
Cider Fortification:
The last method I experimented with was fortifying my cider with a spirit. I refer to these types of ciders as mistelles. This was my Ruby Reaper cider mistelle. I place it in the dessert hard cider category along with ice cider, chaptalized honey cysers, and similar higher alcohol variants. My method again used a cider from my yeast mutation experiments. I racked this cider when the specific gravity was around 1.015. I added organic tequila along with my citrus juices, peels, and the pepper tea. This one I aged for several months. This is a case where you kill the yeast through alcohol intolerance. Most yeast die as the alcohol level increases. My goal was to kill it by inflating the alcohol level above the yeast’s tolerance. I targeted around 12% ABV and used a low tolerant ale strain. Again, I had success with this method. I am sure the additional acid from the citrus also helped. This cider mistelle is plain awesome. I even had people who don’t like adjunct cider or tequila tell me it was good (you know who you are).
Ultimately, there are a number of ways to achieve some residual sweetness. They may not always work and you do need to take precautions, especially when dealing with high pressure. I will continue to explore this area of hard cider but, not because I am extremely interested in making sweet hard ciders. I actually like mine to be relatively dry. However, I am a big advocate of balance and balance means controlling sweetness, acid, tannins, and aroma. Having tools available to me so I can tweak these core elements are what allow the creation of great craft cider. My passion is figuring out how I can use what is local to me to create the best quality cider I can. I hope you enjoyed this article and maybe I inspired you to experiment with some of these ideas. Let me know what you find out and look for more articles on cider because PricklyCider.com is your source for all things cider.
(1) Zeki Berk, Chapter 25 – Chemical Preservation, Food Process Engineering and Technology, Academic Press, 591-606, 2013
(2) E. Juarez-Enriquez and associates, Shelf life studies on apple juice pasteurised by ultrahigh hydrostatic pressure, LWT – Food Science and Technology 62 (2015)
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