Many craft breweries these days are managing a wide range of yeasts and other fermentative organisms under their roof. This is largely due to customer demand for a variety of beer styles, and for continuous innovation in new product categories. Managing many microbes under one roof can present a lot of operational and quality challenges for a busy craft brewery.
The aim of this article is to outline the approaches taken at Escarpment Laboratories to manage many different microbes, with a specific focus on mitigating the risk of cross-contamination and monitoring for contaminations. We think this approach could be translated into a brewery as well.
Like many breweries, Escarpment Labs produces products using many different types of microbes, all under the same roof and sometimes using shared equipment. These product categories could include clean ale strains (e.g. Cali Ale), diastatic yeasts (e.g. Old World Saison) as well as souring bacteria (Lactobacillus). This presents serious challenges to maintaining a facility with a low risk of cross-contamination.
We take a proactive and preventative approach to quality. As an example, we made efforts in 2018 to move all production of diastatic yeasts (S. cerevisiae var. diastaticus) to a dedicated propagator, which can help prevent the risk of cross-contamination of this yeast into other yeast streams, which can be catastrophic in outcome if they get into a “clean” strain.
To this end, we use what we call a “risk level” system. Products are categorized by both the risk posed by contamination, and by these products contaminating other products. Clean ale strains (non-phenolic, non-diastatic) are categorized as Level 1, meaning these are the most sensitive products. Phenolic but non-diastatic ale strains (e.g. Weizen yeasts) are categorized as Level 2, meaning they can cause off-flavours if they contaminate Level 1 yeasts. Diastatic yeasts, Brettanomyces, and bacteria are all categorized as Level 3. If any of these products contaminate the levels above them, serious issues can arise.
All internal materials related to these yeasts are colour coded according to the risk level (green, grey, red) so that errors are less likely to occur. We package yeast with this order in mind; clean yeasts are always packaged first, followed by Level 2 and Level 3. We also tend to have one person at a time devoted to handling Brettanomyces and bacteria. Since this person does not handle clean yeasts during days where they are handling Level 3 products, there is a lower risk of cross-contamination.
Breweries can adopt these measures, and some do. For example, the Crooked Stave Artisan Beer Project uses colour-coded gaskets, valves, and hoses to separate sour, Brett, and clean beer within the same facility, using a similar risk level system.
We think the risk level system has helped us to achieve a low contamination rate. We perform genetic sequence identification (species level) on every microbe we sell, and screen Saccharomyces yeasts for POF (phenolic off-flavour; ferulic acid agar) and STA1 PCR (diastaticus marker gene) as criteria for determining risk level prior to entering commercial propagation.
A yeast carboy (not much left there!) with an exception tag on it. This is a great tool to remind staff of SOP exceptions that have happened during a batch.
We take process deviations seriously as well. If a yeast production process deviates from the standard operating procedure, the batch is tagged with an "exception tag" which documents the SOP deviation. These tags alert and remind employees that there has been an SOP deviation and that extra care needs to be taken with the product in question.
Beyond preventative measures, we also use a rigorous QC screening program. We plate our yeast at three distinct points in the process: in the starter (itself a kind of Carlsberg flask), in the propagator (during aerobic propagation), and as harvested yeast slurry. A batch of yeast must pass these three checkpoints in order to be cleared for delivery to customers. We take QC discrepancies seriously and will double-check and hold product if any staff have any concerns.
An example of a WLN agar plate showing yeast cross-contamination
Currently, our QC screening program centres on agar plating. We use WLN to assess yeast purity (it differentiates between strains based on colony colour), LCSM to screen for wild/diastatic yeasts, and MRS to screen for lactic acid bacteria. If yeast colonies appear on LCSM, they can be tested same-day for STA1 (diastaticus marker gene) using colony PCR. If bacteria appear on MRS plates, we can perform rapid tests to determine a likely identity of the contaminant. We are actively working with external stakeholders to develop enhanced screening procedures for high-risk organisms, and it is likely that our QC program will evolve as these tools become available.