SAP TREATMENT ANALYSIS
TO ELIMINATE BUD TASTE IN MAPLE SYRUP
Syrup with a bud taste (buddy flavoured syrup) is difficult to market under current sales conditions. This lack of popularity is also reflected in the price offered for this type of syrup in the marketing agreement: $1.80/lb if it is pasteurized and $1.25/lb if it is not. The latter option was tested for the 2019 harvest following favourable market responses observed during the release of a special sales statement issued by the Producteurs et produrices acéricoles du Québec (PPAQ). Despite this market development work, some maple syrup producers and maple syrup advisors are working to modify their end-of-season maple syrup in order to improve its organoleptic properties and avoid bud syrup production. While these efforts are admirable, it appears that they create more problems than they solve. The practices described below have led maple syrup buyers to be wary of certain categories of defects. It is in this context that the Centre ACER was called upon to study certain prevention techniques used in the field or found in the scientific literature of the food and maple syrup industry.
What causes the buddy flavour?
Before working to eliminate a problem, it is generally necessary to understand its cause in order to effectively address it. Thus, work analyzing the physicochemical properties of sap leading to the production of a bud-flavoured maple syrup has been carried out by the Centre ACER as well as by Laval University. This work has identified a strong correlation between the presence of amino acids and buddy flavour and has linked these amino acids to the removal of maple dormancy.
It should be noted that any approach to prevent the development of buddy flavour should have a significant effect on amino acids given the link between these compounds in sap and this particular flavour in maple syrup.
How to identify buddy syrup?
In order to be able to describe buddy syrup in a quantitative way, it appeared necessary to identify a chemical marker of buddy flavour. This chemical marker alone does not explain the buddy flavour, but its presence in maple syrup allows it to be classified as a bud in an almost systematic way. The molecule identified as a chemical marker of buddy flavour by researchers at the Centre ACER is dimethyl disulphide, also known as DMDS. Therefore, the more abundant the DMDS is in a maple syrup, the more pronounced the buddy flavour.
What is the “treatment” of sap or sap concentrate?
The treatment of sap or sap concentrate consists of any procedure applied to the sap that deviates from standard production practices (harvesting, concentration and evaporation in a relatively short time). In this case, these practices are performed to prevent the development or mask the taste of buds in maple syrup. The field practices we studied generally involve an aeration or mixing mechanism to increase the oxygen content of the sap in order to promote the development of microorganisms in it or to oxidize certain components. This practice may also be aimed at developing inverted sugars in sap or sap concentrate. It is important to note here that these practices were developed when information on the relationship between amino acids was not yet known; rather, they were intended to address a perceived link in the field between bud syrup production and the conditions typical of high-performance maple groves:
- waterproof and high vacuum operated harvesting system;
- very clean collection and processing system;
- quick processing of sap into maple syrup.
In practice, the sap treatments developed in the field generally involve recirculation of the sap or sap concentrate by means of a pump. This recirculation can be done through perforated pipes, degassing columns from the fishing industry or fountains. The use of the air injector in sap tanks has also been reported, but this practice seems to us to be the most problematic given the issue related to the quality of the air used to supply these devices.
In order to study the effect of sap and sap concentrate treatments on the properties of maple syrup resulting from the application of these techniques, three projects have been set up:
Laboratory study: This study analyzed several types of treatments, including various aeration and recirculation patterns with or without interaction with microorganisms. All this was done under highly controlled laboratory conditions, on sap that reliably produced a low buddy syrup. Various levels of dissolved oxygen and inverted sugar were obtained during these processes. All treatments were repeated twice to validate their reliability and physicochemical and sensory analyses of the maple syrups produced made it possible to properly characterize the situation.
Case study: This study found the effects of a treatment on sap concentrates at different °Brix as applied by a maple syrup producer. Various high flow recirculation times in the concentrate tank were applied by the producer. To confirm the effectiveness of the treatment, a sample of maple syrup was produced in a small cauldron before the treatment was applied; it was then possible to confirm its effectiveness by comparing the syrup produced following aeration with the non-aerated control. Maple syrups were subjected to physicochemical and sensory analyses and a 6‑month stability study.
Exploratory study: This study, conducted in partnership with a maple syrup consultant, resulted in the harvesting of several mid-season and late season maple syrups. These have been produced with different techniques to prevent the development of the buddy flavour, including aeration and modulation of the evaporator parameters to increase the residence time in the evaporator. The maple syrups were harvested by the consultant and then analyzed by the Centre ACER in the context of a stability study. Thus, physicochemical and sensory analyses were carried out upon receipt, following pasteurization (to allow stable storage at room temperature and to measure the effect of this production step) and after 6 months of storage.
What can be concluded from the effect of aeration/fermentation techniques for sap
or sap concentrate on the quality of maple syrup
The projects presented above studied the effects of sap aeration or sap concentrate on the production of maple syrup with low intensity buddy flavours and relatively low DMDS levels. The treatments studied sometimes had a downward effect on the amino acid and DMDS content in syrups, but did not eliminate them completely. Also, these treatments could occasionally, but not repeatedly, modify the flavour rating of the syrup compared to the control (most often from √R5 to √R4 when there were changes). This lack of repeatability makes it possible to affirm that the treatments used in the field are poorly configured and poorly controlled.
Furthermore, the syrups studied presented a new problem: the reappearance of the buddy flavour after a relatively short storage period (6 months). In summary, some of the syrups produced using the aeration techniques studied had a non-bud flavour rating (OK, √, √R1 or √R4) at the outlet of the evaporator while they tasted buddy after a few months of storage. Although it is impossible to quantify this instability reliably to date, the exploratory study nevertheless makes it possible to affirm that this problem is very real and not negligible. In fact, 3% of the 96 syrups received in this study tasted buddy when they were received. This proportion increased to 13% after pasteurization and 6 months of storage. Other occurrences of a return of the buddy flavour following the sale of the syrup have been reported; this change in taste during storage has already led to a product recall.
Given the limited effect of sap treatments on amino acids (presumed precursors of bud taste), the lack of repeatability of treatments reflecting poorly defined treatment parameters and the instability of the flavour produced using these techniques, it is impossible for the Centre ACER to recommend this approach at this time. However, research is continuing to better understand buddy syrup and the factors leading to its production in an effort to find a solution to this problem.
Author: Martin Pelletier, Ing. f. (Forest Engineer) in collaboration with Fadi Ali, Eng., Ph. D., Luc Lagacé, Ph. D. and Nathalie Martin, Chemist, Ph. D.