Safe Home Fermentation

What is fermentation?

Fermentation is one of the oldest and simplest ways to safely preserve food. Fermentation harnesses safe microbes that exist naturally around us and utilises their natural activity to transform natural carbohydrates into acids, gases and/or alcohol. In lacto-fermentation, it is the action of lactic acid bacteria (the good bacteria) that convert natural fruit and vegetable sugars into lactic acids. This increases the acidity to create an environment that removes harmful microbes from fermented foods. At the same time, increased acidity creates flavour and textures that are delicious, and lets us safely store food for several weeks, or even years!

For home kitchens, tried and tested ferment favourites include sauerkraut and kimchi, kombucha and water kefir, yoghurt and milk kefir, and traditional pickles. Read on to learn more about how to start home fermentation safe, and produce natural foods at home that have well-known health benefits for the immune system.

What are the benefits of fermented foods?

When made safely, fermented foods:

1. Support gut health by providing live beneficial bacteria and organic acids.
2. Preserve food and extend shelf life by lowering the pH to 4.6 or below.
3. Add complexity to your meals – sourness, fizz, and depth of flavour that simple, fresh ingredients are unable to offer.

It’s important to remember that “fermented” does not automatically mean safe or healthy. The methods used to create the fermented foods must be well controlled to get great results – safe, healthy and delicious fermented foods.

What foods can I ferment at home?

Safe home ferments typically include:

• Sauerkraut and kimchi (salted, shredded vegetables for lacto fermentation).
• Pickles (cucumbers and other vegetables in salt brine).
• Kombucha (sweetened tea fermented with a SCOBY culture).
• Water kefir (sweetened water fermented with water kefir culture).
• Yoghurt (pasteurised milk fermented with a defined starter culture).
• Milk kefir (pasteurised milk fermented with milk kefir culture)

Key principles for safe home fermentation

There are several key principles that apply to all types of fermentation, regardless of whether the fermentation is aerobic (needs air) or anaerobic (needs no air). Following these principles will get the best possible outcomes by making sure that the initial microbes are the ones that your recipe needs. Then you can be confident that microbial fermentation will safely develop to favour beneficial bacteria over any spoilage microorganisms.

• Use researched and tested ingredient quantities and ratios.
• Don’t improvise the required ratios of salt, sugar or time.
• Table salt is not always the best salt to use – salt with no additives is critical.
• Start with good quality fresh ingredients – no spoilage, bruising or damage.
• Keep equipment and surfaces clean – hands, knives, surfaces and containers.
• Wash all equipment in hot, soapy water before use, and rinse thoroughly with fresh water to remove any soap residue.
• Use the appropriate starter cultures at the correct concentrations recommended.
• For salted ferments, make sure the salt concentration is always between 2-3% of the weight of the prepared vegetables.
• Aim for an end pH level of 4.6 or lower by the end of the recommended fermentation time period for the specific ferment. 

What temperature is best for fermentation?

Temperature is central to safety, as well as to the final flavour of your fermented food or beverage. Different fermentation microbes favour different temperature ranges, check the table below for more information for the ideal temperature ranges.

At home, managing a stable room temperature can be one of the trickiest parts of mastering the fermentation process. Relying on an open kitchen bench will always yield variable results, dependent on the climate you live in, the ambient temperature in the kitchen, the variation between day and night temperature gradients, and the weather of the day. Sometimes these gradients can be somewhat managed at home by using a hot water cupboard or insulated containers, with the aid of a temperature logger. 

There are several affordable aids that can help, such as heating mats and belts, insulated wraps, water baths and controlled incubators. What method you select will depend on your budget, but being able to manage a stable temperature with minimal gradient changes is key. Stable temperature within the correct range for the microbes needed will support those microbes to thrive and to produce good quality acid levels, and delicious home ferments. 

What is the easiest fermented food or beverage to make at home?

For most home fermenters, the simplest starting points are:

• Fermented Food: Sauerkraut or mixed veg in brine
• Fermented Beverage: Kombucha tends to be the most resilient

Both ferments will allow you to focus on the core skills without dipping into great technicalities – correct ratios of key ingredients, good hygiene, temperature control, and watching for the aroma changes over time.

What equipment do I need for home fermentation?

Home fermentation can be done with the simplest of equipment, after all, fermented foods have been made by humans for literally thousands of years – well before heating mats were ever invented! But a few basics for today’s kitchens will matter for any home fermenter who wants to get great results the first time:

• Food grade containers that are glass, ceramic, or high-quality stainless steel.
• Lids with functional airlocks for lacto-ferments that don’t want air (e.g. sauerkraut).
• Breathable lids or cotton tops for aerobic ferments that do want air (e.g. water kefir).
• Fermentation weights that keep vegetables submerged in the brine.
• Clean, sharp and functional utensils (knives, sieves, measures).
• Scales to accurately measure the correct weights and ratios of ingredients.
• pH measures (meters or strips) to verify that fermentation has finished to a safe pH level within the recommended time frame (pH ≤3.6).
• For dairy ferments and beverages, use a safely produced starter culture such as those available from Symbiota, and follow the included instructions for the best and safest results, (pH ≤4.6)

Glass vs ceramic crocks in fermentation

Glass jars are often used for food fermentation because they are cheap and easily accessible, easy to clean, and allow you to see what is happening inside the ferment over time. However, the ferments are more susceptible to wide variations in temperature gradients in a home kitchen, as glass is a poor insulator. It is important to check glass for any cracks or chips, and if any glass has broken into a fermented food – both the fermented food and the glass jar will need to be discarded to ensure safety.

Ceramic crocks are most often selected by experienced home fermenters, as they produce consistently high-quality results, and are good at insulating against the wide variations of temperature in a home kitchen. Although they are a financial investment, it is a good investment for any home cooks that are going to ferment regularly in their home kitchens. It is important to check that ceramic crocks are certified for food-grade fermentation and are free from any cracks or chips that will affect food quality and safety. 

High-quality stainless-steel containers can be used if it is a food grade stainless steel. However, any other metal containers are never recommended for food fermentation because of high acid levels causing metal reactions – which will be unsafe and can affect both colour and flavour of the final ferment.

What is the best salt for fermentation?

Fermentation salt does so much more than season for flavour – it shapes the microbial environment and is critical for success of the final fermented food. There are three key principles that should be considered when selecting a good quality salt and water for the fermentation of foods:

1. Use natural salts: It is best to use a sea salt or a natural rock salt that has no other ingredients and has not been highly refined.
2. Avoid iodised salts: Iodine is a well-known preservative, used for this purpose frequently across medical, scientific and industrial fields. Iodine will inhibit the production of healthy fermentation microbes and must not be present in any amount of salt used for home fermentation.
3. Avoid additives: Some salt preparations include additives such as anti-caking agents which can interfere with fermentation and alter the flavour and texture of the finished product.

How to store fermented foods safely

Once your ferment has reached a pH of 3.6 or below and is at a flavour and acidity level that you enjoy, selecting the best method of storage becomes the next safety step. Cold storage and clear labelling are the most crucial tasks to complete to avoid over-fermentation. Move through the following checklist to make sure you have all the safety bases well covered:

• Process the finished ferment as necessary to reach the desired final product (strain, flavour, etc).
• Transfer the finished ferment into clean glass containers with suitable lids, and make sure the seal is tight.
• Label each container with the name of the product and the date of fermentation, so that future you will know the age of any forgotten jars at the back of the fridge.
• Move the ferments into cold storage – usually into a refrigerator – this will slow any further microbial activity and reduce the risk of explosions or overly-acidic finished ferments.
• Fermented vegetables can be safely refrigerated for up to 18 months.
• Non-dairy beverage ferments can be safely refrigerated for up to 12 months.
• Dairy ferments can be safely refrigerated for up to 4 weeks.

How to tell if fermented food is safe to eat.

Honestly, daily observation with your eyes, nose and taste buds are your best tools for the home kitchen. You will not be in any doubt if the ferment is showing any of the unsafe indicators below. The key principles to check for are as follows:

If it doesn’t look right – throw it out. Clean everything thoroughly and start again.

Tips for safe fermentation

Bringing this together for the most common home ferments, it is important to follow key steps to support the safe production of healthy microbes and their associated organic acids. This will prevent issues such as mould and spoilage, overly acidic ferments, or ferments that fail to attain the necessary acidity quickly enough. Follow these tips to be sure you are practicing safe fermentation at home:

• Follow verified recipes from trusted sources.
• Don’t guess on the ingredient ratios, temperatures or fermentation times.
• Practice good quality hygiene for yourself and your equipment.
• Use professional starter cultures from safe sources such as those provided by Symbiota.
• Keep vegetable lacto-ferments free from oxygen (anaerobic) by submerging the vegetables in brine, using fermentation weights and minimising oxygen exposure with airlock lids.
• Keep aerobic ferments open to oxygen by using breathable covers like cotton tops with elasticated edges.
• Monitor room or fermentation container temperatures using a proper thermometer.
• Manage fermentation temperatures using methods that suit your climate and budget.
• Invest in pH measuring equipment so that you can be sure that your finished ferment has reached pH ≤3.6 within the recommended fermentation time period.
• Use pasteurised milk for any dairy ferments – unpasteurised milk contains microbes that may compete with the fermentation cultures if not completely fresh. If you want to use raw milk, make sure it is very fresh and not had time for its own microbes to flourish and therefore outcompete starter culture microbes. 

Troubleshooting difficult ferments

If something feels off, it is important to trust your senses and delve into what could have caused the issue so you can correct your method for the next ferment. These are the common areas to check and consider:

1. Salt too low:

Soft, mushy vegetables, odd smells, slimy brine.

2. Temperature too high:

Soft, mushy vegetables, too much acid production.

3. Temperature too low:

Too crunchy vegetables, not enough acid production.

4. Poor submersion:

Floating vegetables, mould growth.

5. Starter issues:

Weak flavours, incomplete fermentation, tired starter cultures needing attention.

6. Ingredient issues:

Chlorinated water, iodised salt, unexpected additives in ingredients.

7. Inadequate final pH:

If pH is well above 3.6 after the fermentation time period, the recommended action is to discard and start again with a tested recipe and fresh, good quality ingredients.

Beginner friendly ferments

It is a wonderful journey to become a kitchen partnership with the natural microbes around us. For a gentle start into fermentation at home, try one of the following ferments to get yourself started. These are tried and tested and beginner friendly fermentation cultures that will teach you the fundamentals without being overly complex or needing fancy equipment. All you will need is the basic awareness, clean glass jars or bottles, a good recipe, and basic temperature awareness. Let’s start with the easy ones:

• Sauerkraut (1-3 vegetables, simple salt-only ferment).
• Cucumber Pickle (1 vegetable in a salt brine).
• Kombucha (water, sugar, tea and Symbiota kombucha scoby).

Easy ferment recipes

Once you are comfortable with the core principles for safe food fermentation at home, you can get started with easy recipes. Make sure the recipes are from reliable sources such as Symbiota and specialised fermentation organisations. Look for a clear ingredient list, specified temperature and fermentation times, pH expectations, and explicit notes on storage conditions and shelf life. If a recipe has all of these, it is more likely to be safe and a good choice for you to get started on.